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| Industrial Effluent & Sewage Treatment System – unit processes, maintenance, troubleshooting and sludge treatment options. A concise understanding of the industrial effluent and wastewater treatment designs and operating principles for enhancement of competency by reviewing vast experience in practice. |
The legal definition stipulates that;
- Effluent as industrial effluent, mixed effluent or sewage.
- Industrial Effluent is defined as any wastewater produced by reasons of production activities.
- Sewage is defined as any wastewater containing animal and vegetable matter in solution or suspension. It simply means faecal or urinal discharges.
- Definasi yang telah ditetapkan dibawah undang-undang;
- Effluent adalah effluent industri, effluent bercampur atau kumbahan.
- Effluen industri adalah air buangan yang dilepaskan diatas sebab-sebab aktiviti pemerosesan/pengeluaran.
- Kumbahan adalah air buangan yang berpunca dari sisa manusia.
Professional engineer undertakes design & construction;
Build and operate as design;
New parameters: e.g. Silver, Aluminium, Selenium, Barium, Fluoride, Formaldehyde, Ammoniacal Nitrogen and Color;
COD varies for specific industry – more achievable;
Full-time competent person – trained and certified by DOE;
Performance monitoring is mandatory;
Best management practices be in practice;
By-pass & dilution is prohibited;
Spills, accidental release or leakage – 6 hours to DOE;
Prohibition order for continued incompliance;
Direct judicial action under the regulation enabled;
Legal liability under Section 25, EQA 1974 - not discussed here.
Water Pollution; overview of significant parameters:
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| Nature of effluent and sewage: inorganic, organic & inorganic, organic; |
Cadmium – used in manufacture of batteries, paints, plastics, plating of iron products e.g. bolts, nuts, as anti-corrosion agent. Health impact upon human – brittle bones & intense pain, high blood, sterility among males, kidney and flu-like disorders. This soft, bluish-white metal is chemically similar to the two other stable metals in group 12, zinc and mercury. Similar to zinc, it prefers oxidation state +2 in most of its compounds and similar to mercury it shows a low melting point compared to transition metals. Cadmium and its congeners are not always considered transition metals, in that they do not have partly filled d or f electron shells in the elemental or common oxidation states. The average concentration of cadmium in the Earth's crust is between 0.1 and 0.5 parts per million (ppm). It was discovered in 1817 simultaneously by Stromeyer and Hermann, both in Germany, as an impurity in zinc carbonate.
Chromium – used in manufacture of alloys, refractories, catalysts, chromic oxide, and chromate salts for the plating industry and paint manufacturing. Chromate poisoning – skin disorders and liver damage – oncogenic i.e. carcinogenic. Virtually all chromium ore is processed via hexavalent chromium, specifically the salt, sodium dichromate. Approximately 136,000,000 kilograms (300,000,000 lb) of hexavalent chromium were produced in 1985.[1] Other hexavalent chromium compounds are chromium trioxide and various salts of chromate and dichromate. Hexavalent chromium is used for the production of stainless steel, textile dyes, wood preservation, leather tanning, and as anti-corrosion and conversion coatings as well as a variety of niche uses. Chromium hexavalent (CrVI) compounds, often called hexavalent chromium, exist in several forms. Industrial uses of hexavalent chromium compounds include chromate pigments in dyes, paints, inks, and plastics; chromates added as anticorrosive agents to paints, primers, and other surface coatings; and chromic acid electroplated onto metal parts to provide a decorative or protective coating. Hexavalent chromium can also be formed when performing "hot work" such as welding on stainless steel or melting chromium metal. In these situations the chromium is not originally hexavalent, but the high temperatures involved in the process result in oxidation that converts the chromium to a hexavalent state.(29 CFR OSHA General Industry 1910)Hexavalent chromium is recognized as a human carcinogen via inhalation.[2] Workers in many different occupations are exposed to hexavalent chromium. Problematic exposure is known to occur among workers who handle chromate-containing products as well as those who perform welding, grinding, or brazing on stainless steel.[2] Within the European Union, the use of hexavalent chromium in electronic equipment is largely prohibited by the Restriction of Hazardous Substances Directive.
Copper – commonly used as Copper Sulphate to control growth of algae in water supply reservoirs – near 1.0mg/L may be toxic to some fish.
Lead – used in service pipes, paints for interior décor, previously in petrol – causes brain and kidney damage. Lead is a soft, malleablepoor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed to air. Lead has a shiny chrome-silver luster when it is melted into a liquid. Lead is used in building construction, lead-acid batteries, bullets and shots, weights, as part of solders, pewters, fusible alloys and as aradiation shield. Lead has the highest atomic number of all of the stable elements, although the next higher element, bismuth, has ahalf-life that is so long (much longer than the age of the universe) that it can be considered stable. Its four stable isotopes have 82 protons, a magic number in the nuclear shell model of atomic nuclei.
Lead, at certain exposure levels, is a poisonous substance to animals. It damages the nervous system and causes brain disorders. Excessive lead also causes blood disorders in mammals. Like the element mercury, another heavy metal, lead is a neurotoxin that accumulates both in soft tissues and the bones. Lead poisoning has been documented from ancient Rome, ancient Greece, and ancient China.
Mercury – used in amalgams, scientific equipments, batteries, arc lamps, extraction of gold & silver, electrolytic production of chlorine, its salts – used as fumigants in herbicides & insecticides. Also used as antifoulants in ship paints and mildew proofing of canvas. In 1950s – Minamata Bay incident – chemical plant – effluent – sea food intake – 111 cases – 43 died – babys from afflicted mother – congenitals defects. Lake St. Clair – US & Canada – Fish – from Chlor-alkali industry – methylated mercury – produced by bacterial action in bottom muds in anaerobic condition. It is also known as quicksilver ( /ˈkwɪksɪlvər/ ) or hydrargyrum ( /haɪˈdrɑrdʒɨrəm/), from "hydr-" water and "argyros" silver. Mercury is the only metal that is liquid at standard conditions for temperature and pressure; the only other element that is liquid under these conditions is bromine. With a freezing point of −38.83 °C and boiling point of 356.73 °C, mercury has one of the narrowest ranges of its liquid state of any metal. A heavy, silvery d-block metal, mercury is the only metallic element that is liquid at room temperature and standard pressure, with elements such as caesium, francium, gallium, and rubidium being liquid just above room temperature or at non-standard pressure.[1][2][3]
Mercury occurs in deposits throughout the world mostly as cinnabar (mercuric sulfide). The red pigment vermilion is mostly obtained by reduction from cinnabar. Cinnabar is highly toxic by ingestion or inhalation of the dust. Mercury poisoning can also result from exposure to water soluble forms of mercury (such as mercuric chloride or methylmercury), inhalation of mercury vapor, or eating seafood contaminated with mercury. Mercury is used in thermometers, barometers, manometers, sphygmomanometers, float valves, some electrical switches, and other scientific apparatus, though concerns about the element's toxicity have led to mercury thermometers and sphygmomanometers being largely phased out in clinical environments in favor of alcohol-filled, digital, or thermistor-based instruments. It remains in use in scientific research applications and in amalgam material for dental restoration. It is used in lighting: electricity passed through mercury vapor in a phosphor tube produces short-wave ultraviolet light which then causes the phosphor to fluoresce, making visible light.
Nickel & Cobalt – used in electroplating – effluent – aquatic environment – oncogenic.
Silver – used in electroplating – usually recovered – expensive – silver poisoning – darkening of skin & eyes.
Arsenic (non-metal) – used in plating operations, refinery, coal coking – widely distributed in natural waters – arsenic eaters – toxic level in human is erratic – suspected to be oncogenic. Selenium – used in manufacture of electrical components, photoelectric cells & rectifiers – oncogenic to human: with poor evidence as some test showed anti-oncogenic – causes improper bone formation in animals i.e. ‘alkali disease’ and ‘blind staggers’.
Ø General scope based treatment objectives;
Detail scopes of primary, secondary & tertiary treatment
Primary Treatment;
- Primary treatment; raw effluent or influent – often contains other contaminant or foreign matters in coarse or bigger sizes e.g. grass-cut debris, fibres of fruit and pulps, scum of fatty matters, resins, adhesives, etc. that may upset the WWTP’s system, such as clogging pumps, valves and pipes.
- Secondary treatment; e.g. in biological systems –anaerobic or aerobic decomposition of organic matters to ideally H2O and CO2 plus dead cells in sludge forms that settles in clarifiers. In chemical treatment – inorganic pollutants removed by coagulation & flocculation – settles – sludge. Tertiary treatment – e.g. removal of dissolved solids, colour, odour, pathogenic organisms, inorganics not removable by conventional chemical treatment, etc. including dewatering and further treatment of sludge.
Comminutors can be used in wastewater treatment to cut up and grind the coarse solids into smaller sizes so that this will eliminate the problems caused towards downstream operations especially clogging happening in pumps. Different from bar racks and coarse screens, it does not involve having to remove any type of solid out from the flow system and thus void the necessity of messy jobs having to clean and handle on solid waste disposal. Its use and application is particular important in treatment plants located in cold climates areas whereby use of comminutors means there will not be any issue with collected waste becoming trapped on freezing screens.
Usually a preliminary study will be carried out to determine what types of solids are normally present and where the wastewater come from and especially from which industry that generates it. Normally based on this information, the manufacturer will build and sized it up accordingly to handle the incoming flow. A vertical rotating system is very common and a typical installation will usually have a revolving drum driven by a motor and inside it, there are multiple sets of moving teeth and shearing bars to tear apart the solids as it gets carried together with the wastewater flow. Other designs of comminuting devices will have individual circular screen rotating in the opposite direction and as large solids passes through, it will be subjected to the shearing force exerted by both the outer and inner screens. The small clearance between the moving and stationary screen will tear apart the solids reducing its size before it can pass through.
Grit remover;
Most systems these days are built right after the grit chamber in order to prolong the life of the moving parts and to reduce wear and tear occurring on the surfaces. Certain wastewater treatment plant will have both manual bar screens and the comminutors working together in parallel and depending on the incoming flow rates; wastewater can be diverted going to either one of it through bypass lines. Other problems related to its application is on the maintenance aspect as high wear and tear will often require frequent changing of the moving parts.
Most of the time, this can be avoided if there are also rock traps built in at the upper channel to prevent material from damaging the cutting blades. Head loss is also another issue as the wastewater passes through the comminutor and thus the overall design of the system has to take this into consideration. The best approach is to consult the manufacturers and bring up this issue and highlight it as part of the requirements. The first step in the treatment of wastewater is known as Preliminary Treatment, which screens out, grinds up, or separates debris in the wastewater. Sticks, rags, large food particles, sand, gravel, toys, plastics, and other objects are removed at this stage to conserve valuable space within the treatment processes and to protect pumping and other equipment from clogs, jams or excessive wear. Treatment equipment such as bar screens, comminutors (a large version of a garbage disposal that shreds material), and grit chambers are used on the wastewater as it first enters a treatment plant. The collected debris is usually disposed of in a landfill. In this lesson we will describe and discuss each of these processes and their importance in the treatment process.
Most systems these days are built right after the grit chamber in order to prolong the life of the moving parts and to reduce wear and tear occurring on the surfaces. Certain wastewater treatment plant will have both manual bar screens and the comminutors working together in parallel and depending on the incoming flow rates; wastewater can be diverted going to either one of it through bypass lines. Other problems related to its application is on the maintenance aspect as high wear and tear will often require frequent changing of the moving parts.
Grit removal; e.g. sand, gravel, cinders, or other heavy solid materials that have subsiding velocities or specific gravities greater than the organic putrescible solids in the effluent – e.g. sugar refinery, fruit-based drinks - uses grit chambers or centrifuge.
The Grit is a general term for coarse particles. BS3405 defines grit as solid particles retained on a mesh BS sieve with pore size of 76um.
Another version where grit remover and oil interceptor is combined in a pre-treatment or primary stage. Apart from occupying less space in its built-up it allows easier maintenance. However its size and retention time is a critical factor to consider as some types of effluent are prone to biological activity, especially, an anaerobic condition towards the bottom of the tank. Suitable for effluent with high coarse and dense impurities plus oily nature e.g. palm oil, drilling mud, sugar-cane, mining, etc.
Oil interceptor;
The API separator is a gravity separation device designed by using Stokes Law to define the rise velocity of oil droplets based on their density and size. The design of the separator is based on the specific gravity difference between the oil and the wastewater because that difference is much smaller than the specific gravity difference between the suspended solids and water. Based on that design criterion, most of the suspended solids will settle to the bottom of the separator as a sediment layer, the oil will rise to top of the separator, and the wastewater will be the middle layer between the oil on top and the solids on the bottom. (Beychok, Milton R. (1967). Aqueous Wastes from Petroleum and Petrochemical Plants (1st Edition ed.). John Wiley & Sons. LCCN 67019834.) Typically, the oil layer is skimmed off and subsequently re-processed or disposed of, and the bottom sediment layer is removed by a chain and flight scraper (or similar device) and a sludge pump. The water layer is sent to further treatment consisting usually of a dissolved air flotation (DAF) unit for further removal of any residual oil and then to some type of biological treatment unit for removal of undesirable dissolved chemical compounds.
Parallel plate separators are similar to API separators but they include tilted parallel plate assemblies (also known as parallel packs).The underside of each parallel plate provides more surface for suspended oil droplets to coalesce into larger globules. Any sediment slides down the topside of each parallel plate. Such separators still depend upon the specific gravity between the suspended oil and the water. However, the parallel plates enhance the degree of oil-water separation. The result is that a parallel plate separator requires significantly less space than a conventional API separator to achieve the same degree of separation.
CPI interceptor
In CPIs the parallel plates are corrugated (like roofing material) with the axis of the corrugations parallel to the direction of flow. The plate pack is inclined at an angle of 45° and the bulk water flow is forced downward. The oil sheet rises upward counter to the water flow and is concentrated in the top of each corrugation. When the oil reaches the end of the plate pack, it is collected in a channel and brought to the oil-water interface. For service temperatures less than 60°C, fiberglass with a steel frame is used. For service temperatures greater than 60°C, corrosion-resistant alloys or stainless steels are recommended.
The Grit is a general term for coarse particles. BS3405 defines grit as solid particles retained on a mesh BS sieve with pore size of 76um.
Another version where grit remover and oil interceptor is combined in a pre-treatment or primary stage. Apart from occupying less space in its built-up it allows easier maintenance. However its size and retention time is a critical factor to consider as some types of effluent are prone to biological activity, especially, an anaerobic condition towards the bottom of the tank. Suitable for effluent with high coarse and dense impurities plus oily nature e.g. palm oil, drilling mud, sugar-cane, mining, etc.
Oil interceptor;
The API separator is a gravity separation device designed by using Stokes Law to define the rise velocity of oil droplets based on their density and size. The design of the separator is based on the specific gravity difference between the oil and the wastewater because that difference is much smaller than the specific gravity difference between the suspended solids and water. Based on that design criterion, most of the suspended solids will settle to the bottom of the separator as a sediment layer, the oil will rise to top of the separator, and the wastewater will be the middle layer between the oil on top and the solids on the bottom. (Beychok, Milton R. (1967). Aqueous Wastes from Petroleum and Petrochemical Plants (1st Edition ed.). John Wiley & Sons. LCCN 67019834.) Typically, the oil layer is skimmed off and subsequently re-processed or disposed of, and the bottom sediment layer is removed by a chain and flight scraper (or similar device) and a sludge pump. The water layer is sent to further treatment consisting usually of a dissolved air flotation (DAF) unit for further removal of any residual oil and then to some type of biological treatment unit for removal of undesirable dissolved chemical compounds.
Parallel plate separators are similar to API separators but they include tilted parallel plate assemblies (also known as parallel packs).The underside of each parallel plate provides more surface for suspended oil droplets to coalesce into larger globules. Any sediment slides down the topside of each parallel plate. Such separators still depend upon the specific gravity between the suspended oil and the water. However, the parallel plates enhance the degree of oil-water separation. The result is that a parallel plate separator requires significantly less space than a conventional API separator to achieve the same degree of separation.
In CPIs the parallel plates are corrugated (like roofing material) with the axis of the corrugations parallel to the direction of flow. The plate pack is inclined at an angle of 45° and the bulk water flow is forced downward. The oil sheet rises upward counter to the water flow and is concentrated in the top of each corrugation. When the oil reaches the end of the plate pack, it is collected in a channel and brought to the oil-water interface. For service temperatures less than 60°C, fiberglass with a steel frame is used. For service temperatures greater than 60°C, corrosion-resistant alloys or stainless steels are recommended.
Grease traps (also known as grease interceptors, grease recovery devices and grease converters) are plumbing devices designed to intercept most greases and solids before they enter a wastewater disposal system. septic tanks and treatment facilities to form a floating scum layer. anaerobic digestion process. However, very large amounts of oil from food production in kitchens of factory canteens and restaurants can overwhelm the septic tank or treatment facility, causing a release of untreated sewage into the environment. Also, high viscosity fats and cooking greases such as lard solidify when cooled, and can combine with other disposed solids to form blockages in drain pipes.
Common wastewater contains small amounts of oils which enter into
This scum layer is very slowly digested and broken down by microorganisms in the
Equalization; the EQ Tank
Equalization Tank
Description: Flow equalization simply is the damping of flowrate variations so that a constant or nearly constant flowrate is achieved. The principal benefits that are cited as deriving from application of flow equalization are as follows:
· Biological treatment is enhanced, because shock loadings are eliminated or can be minimized, inhibiting substances can be diluted, and pH can be stabilized The effluent quality and thickening performance of secondary sedimentation tanks following biological treatment is improved through constant solids loading.
· Effluent - filtration surface - area requirements are reduced, filter performance is improved, and more uniform filter - backwash cycles are possible Equalization Tank
Description: Flow equalization simply is the damping of flowrate variations so that a constant or nearly constant flowrate is achieved. The principal benefits that are cited as deriving from application of flow equalization are as follows:
· Biological treatment is enhanced, because shock loadings are eliminated or can be minimized, inhibiting substances can be diluted, and pH can be stabilized The effluent quality and thickening performance of secondary sedimentation tanks following biological treatment is improved through constant solids loading.
· In chemical treatment, damping of mass loading improves chemical feed control and process reliability
In practice, the volume of the equalization tank will be larger than that theoretically determined to account for the following factors:
Continuous operation of aeration and mixing equipment will not allow complete drawdown, although special structures can be built
Volume must be provided to accommodate the concentrated plant recycle streams that are expected, if such flows are returned to the equalization tank (a practice that is not recommended because of the potential to create odour) Some contingency should be provided for unforeseen changes in diurnal flow
Operational Data of the Equalization Tank
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Hours
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Inflow (m3)
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Outflow (m3)
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Cumulative Inflow (m3)
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Cumulative Outflow (m3)
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Cumulative Difference
(m3)
|
00 - 01
|
0.00
|
8.33
|
0.00
|
8.33
|
- 8.33
|
01 - 02
|
0.00
|
8.33
|
0.00
|
16.66
|
- 16.66
|
02 - 03
|
0.00
|
8.33
|
0.00
|
24.99
|
- 24.99
|
03 - 04
|
0.00
|
8.33
|
0.00
|
33.32
|
- 33.32
|
04 - 05
|
0.00
|
8.33
|
0.00
|
41.65
|
- 41.65
|
05 - 06
|
0.00
|
8.33
|
0.00
|
49.98
|
- 49.98
|
06 - 07
|
0.00
|
8.33
|
0.00
|
58.31
|
- 58.31
|
07 - 08
|
0.00
|
8.33
|
0.00
|
66.68
|
- 66.68
|
08 - 09
|
17.40
|
8.33
|
17.40
|
75.01
|
- 57.61
|
09 - 10
|
26.80
|
8.33
|
44.20
|
83.34
|
- 39.14
|
10 - 11
|
23.00
|
8.33
|
67.20
|
91.67
|
- 24.47
|
11 - 12
|
19.30
|
8.33
|
86.50
|
100.00
|
- 13.50
|
12 - 13
|
13.20
|
8.33
|
99.70
|
108.33
|
- 8.63
|
13 - 14
|
15.60
|
8.33
|
115.30
|
116.66
|
- 1.36
|
14 - 15
|
23.10
|
8.33
|
138.40
|
124.99
|
+ 13.41
|
15 - 16
|
21.10
|
8.33
|
159.50
|
133.32
|
+ 26.18
|
16 - 17
|
21.10
|
8.33
|
180.60
|
141.65
|
+ 38.95
|
17 - 18
|
19.40
|
8.33
|
200.00
|
150.02
|
+ 49.98
|
18 - 19
|
0.00
|
8.33
|
200.00
|
158.35
|
+ 41.65
|
19 - 20
|
0.00
|
8.33
|
200.00
|
166.68
|
+ 33.32
|
20 - 21
|
0.00
|
8.33
|
200.00
|
175.01
|
+ 24.99
|
21 - 22
|
0.00
|
8.33
|
200.00
|
183.34
|
+ 16.66
|
22 - 23
|
0.00
|
8.33
|
200.00
|
191.67
|
+ 8.33
|
23 - 24
|
0.00
|
8.33
|
200.00
|
200.00
|
0.00
|
VEqualization
tank = 66.68 + 49.98 =
116.66 m3
Continuous Mixing in Equalization Tank...
In continuous mixing, the principal objective is to maintain the contents of a reactor of holding tank in a completely mixed state. Continuous mixing can be accomplished in a number of different ways, including; (1) in hydraulic jumps in open channels, (2) in "Venturi" flumes, (3) in pipelines, (4) by pumping, (5) with static mixers and (6) mechanical mixers. According to the literature, the completely mixed regime can be obtained in a equalization tank, by applying a power varying between 10 and 30 W / m3. Continuous mixing in the equalization tank was accomplished by a submerged mechanical mixer having a power of 4 kW.
Primary clarification; clarifier tanks
Primary aeration;
DAF can be categorized by Circular (more efficient) and Rectangular (more residence time). The former type requires just 3 minutes and the example is Wockoliver DAF system, whereas Rectangular requires 20 to 30 minutes the typical example can be syskill DAF system. One of the bigger advantage of Circular is its Spiral Scoop.
Operating Principle
Air under pressure is dissolved into water according to Henry's Law of Dissolution. Releasing the pressure back to STP via a special device creates millions of microbubbles approximately 30-100 microns in diameter. The microbubbles attach to floc in the water and float it to the surface for removal.
Features
High Loading - Rates 4-6 gpm/sf.
Reduced Chemical Comsumption - Formation of a large, rapidly settling floc is not required, saving money.
High Sludge Concentrations - Dewatering can occur without additional thickening, eliminating expensive sludge thickeners.
Rapid Start-Up - Good-quality water can be produced within 45 minutes of start-up.
Compact Design - Requires less space than conventional processes.
Secondary Treatment;
Attached growth; - trickling filter
A trickling filter consists of a fixed bed of rocks, lava, coke, gravel, slag, polyurethane foam, sphagnum peat moss, ceramic, or plastic media over which sewage or other wastewater flows downward and causes a layer of microbial slime (bio-film) to grow, covering the bed of media. Aerobic conditions are maintained by splashing, diffusion, and either by forced air flowing through the bed or natural convection of air if the filter medium is porous. The terms trickle filter, trickling biofilter, biofilter, biological filter and biological trickling filter are often used to refer to a trickling filter. These systems have also been described as roughing filters, intermittent filters, packed media bed filters, alternative septic systems, percolating filters, attached growth processes, and fixed film processes.
Sewage treatment trickle filters
Onsite sewage facilities (OSSF) are recognized as viable, low-cost, long-term, decentralized approaches to sewage treatment if they are planned, designed, installed, operated and maintained properly (USEPA, 1997).
Sewage trickling filters are used in areas not serviced by municipal wastewater treatment plants (WWTP). They are typically installed in areas where the traditional septic tank system are failing, cannot be installed due to site limitations, or where improved levels of treatment are required for environmental benefits such as preventing contamination of ground water or surface water.
Sites with a high water table, high bedrock, heavy clay, small land area, or which require minimal site destruction (for example, tree removal) are ideally suited for trickling filters.
All varieties of sewage trickling filters have a low and sometimes intermittent power consumption. They can be somewhat more expensive than traditional septic tank-leach field systems, however their use allows for better treatment, a reduction in size of disposal area, less excavation, and higher density land development.
Industrial wastewater treatment trickle filters
Wastewaters from a variety of industrial processes have been treated in trickling filters. Such industrial wastewater trickling filters consist of two types:
Large tanks or concrete enclosures filled with plastic packing or other media.[1]
Vertical towers filled with plastic packing or other media.[2][3]
The availability of inexpensive plastic tower packings has led to their use as trickling filter beds in tall towers, some as high as 20 meters.[4] As early as the 1960s, such towers were in use at: the Great Northern Oil's Pine Bend Refinery in Minnesota; the Cities Service Oil Company Trafalgar Refinery in Oakville, Ontario and at a kraft paper mill.[5]
The treated water effluent from industrial wastewater trickling filters is very often subsequently processed in a clarifier-settler to remove the sludge that sloughs off the microbial slime layer attached to the trickling filter media (see Image 1 above).
Currently, some of the latest trickle filter technology involves aerated biofilters which are essentially trickle filters consisting of plastic media in vessels using blowers to inject air at the bottom of the vessels, with either downflow or upflow of the wastewater.[6]
The goal of a primary clarifier is to remove sediment by using gravity, much like the grit chambers. As the wastewater enters the tank, it allows for these larger particles to settle. This settling process is aided by the addition of chemicals. The particles and chemicals that settle to the bottom are then sent to the sludge collection well, and the wastewater continues on to activated sludge. After being screened, in one case of a sewage treatment, the wastewater enters two 45-foot diameter, 140,000-gallon tanks called clarifiers. Here the biosolids are allowed to settle to the bottom of the tank. The solids are eventually pumped out of the tank and stored for later treatment. Between 15 and 40 percent of the solids are removed at this stage, which takes about 4.5 hours.
Primary sedimentation tanks shall be designed for:
maximum surface loading of 40 m3/m2/d at peak flow,
minimum retention time of 2 hours at peak flow,
maximum weir loading of 250 m3/m/d at peak flow.
Final sedimentation tanks shall be designed for:
maximum surface loading of 35 m3/m2/d at peak flow if they are preceded by Rotating Biological Contactor (RBC) or biological filters,
maximum surface loading of 22 m3/m2/d at peak flow if they are preceded by the extended aeration process,
minimum retention time of 2 hours at peak flow.
The reduction of total BOD by different stages of the primary treatment processes should be taken as follow:
equalization tank-nil
coarse screen-nil
fine screen (max. opening 2 mm)-7.5%
primary sedimentation-30%
fine screen and primary sedimentation-30%
The net BOD load going into the subsequent biological processes should be computed accordingly.
RBC (Rotating Biological Contractor): 10 g total BOD/m2/d (i.e. per sq.m. of RBC surface) entering into the RBC or as recommended by manufacturer, whichever is smaller.
Extended aeration: 0.07 kg total BOD/kg MLSS/d and MLSS in the range between 2 000 and 3 500 mg/L
Plastic biological filter (Bio-filter): 0.5 kg total BOD/m3/d (i.e. per cu.m. of media volume) or as recommended by manufacturer, whichever is smaller.
For other biological treatment methods, such as sequential batch reactor, contact stabilization and other patented processes etc., organic loadings proposed in the design should be justified based on its previous Wastewater-Characterization-Study.
Settling
While a degree of clarification can be accomplished by subsidence (settling), most industrial processes require better quality water than can be obtained from settling only. Most of the suspended matter in water would settle, given enough time, but in most cases the amount of time required would not be practical. The time required for settling is dependent on many factors, including:
1. Weight of the particle
2. Shape of the particle
3. Size of the particle
4. Viscosity and/or frictional resistance of the water, which is a function of temperature
The settling rates of various size particles at 50 ºF (10 ºC) is illustrated in the Table that follows;
Stokes' Law
Settling velocities may be calculated from Stokes' Law.
V = 2662(S1 - S2),D2 / z
Where V = Velocity of fall (ft/sec)
D = Diameter of particle (in)
S1= Density of particle (lb/ft3)
S2= Density of fluid (lb/ft3)
z = Viscosity (centipoises)
In this equation it is assumed that the particles are spherical, failing under viscous resistance, and that they have no electrostatic charges. This is, of course, never true under actual conditions. Most suspended solids smaller than 0.1 mm found in surface waters carry negative electrostatic charges. This charge causes the particles to repel each other, increasing their stability and thus increasing their tendency to remain suspended. Chemicals are often added to water to neutralize particle charge and enhance particle settling. Chemicals used to promote suspended particle subsidence in the clarification process are commonly called coagulants; the particle charge neutralization process is called coagulation. (Reference from: GC3 SPECIALTY CHEMICALS, INC.)maximum surface loading of 40 m3/m2/d at peak flow,
minimum retention time of 2 hours at peak flow,
maximum weir loading of 250 m3/m/d at peak flow.
Final sedimentation tanks shall be designed for:
maximum surface loading of 35 m3/m2/d at peak flow if they are preceded by Rotating Biological Contactor (RBC) or biological filters,
maximum surface loading of 22 m3/m2/d at peak flow if they are preceded by the extended aeration process,
minimum retention time of 2 hours at peak flow.
The reduction of total BOD by different stages of the primary treatment processes should be taken as follow:
equalization tank-nil
coarse screen-nil
fine screen (max. opening 2 mm)-7.5%
primary sedimentation-30%
fine screen and primary sedimentation-30%
The net BOD load going into the subsequent biological processes should be computed accordingly.
RBC (Rotating Biological Contractor): 10 g total BOD/m2/d (i.e. per sq.m. of RBC surface) entering into the RBC or as recommended by manufacturer, whichever is smaller.
Extended aeration: 0.07 kg total BOD/kg MLSS/d and MLSS in the range between 2 000 and 3 500 mg/L
Plastic biological filter (Bio-filter): 0.5 kg total BOD/m3/d (i.e. per cu.m. of media volume) or as recommended by manufacturer, whichever is smaller.
For other biological treatment methods, such as sequential batch reactor, contact stabilization and other patented processes etc., organic loadings proposed in the design should be justified based on its previous Wastewater-Characterization-Study.
Settling
While a degree of clarification can be accomplished by subsidence (settling), most industrial processes require better quality water than can be obtained from settling only. Most of the suspended matter in water would settle, given enough time, but in most cases the amount of time required would not be practical. The time required for settling is dependent on many factors, including:
1. Weight of the particle
2. Shape of the particle
3. Size of the particle
4. Viscosity and/or frictional resistance of the water, which is a function of temperature
The settling rates of various size particles at 50 ºF (10 ºC) is illustrated in the Table that follows;
Stokes' Law
Settling velocities may be calculated from Stokes' Law.
V = 2662(S1 - S2),D2 / z
Where V = Velocity of fall (ft/sec)
D = Diameter of particle (in)
S1= Density of particle (lb/ft3)
S2= Density of fluid (lb/ft3)
z = Viscosity (centipoises)
Introduction
Treatment of wastewater using an oxidation ditch is relatively similar to wastewater treatment in a packaged plant. But the oxidation ditch replaces the aeration basin and provides better sludge treatment.
Treatment of wastewater using an oxidation ditch is relatively similar to wastewater treatment in a packaged plant. But the oxidation ditch replaces the aeration basin and provides better sludge treatment.
Oxidation ditch
The only pretreatment typically used in an oxidation ditch system is the bar screen. After passing through the bar screen, wastewater flows directly into the oxidation ditch.
The oxidation ditch is a circular basin through which the wastewater flows. Activated sludge is added to the oxidation ditch so that the microorganisms will digest the B.O.D. in the water. This mixture of raw wastewater and returned sludge is known as mixed liquor.
Oxygen is added to the mixed liquor in the oxidation ditch using rotating biological contactors (RBC's.) RBC's are more efficient than the aerators used in packaged plants. In addition to increasing the water's dissolved oxygen, RBC's also increase surface area and create waves and movement within the ditches. Once the B.O.D. has been removed from the wastewater, the mixed liquor flows out of the oxidation ditch. Sludge is removed in the clarifier. This sludge is pumped to an aerobic digester where the sludge is thickened with the help of aerator pumps. This method greatly reduces the amount of sludge produced. Some of the sludge is returned to the oxidation ditch while the rest of the sludge is sent to waste.
Comparison to a Packaged Plant
The treatment of wastewater in an oxidation ditch is similar to treatment in a packaged plant. The two main differences between the processes are the retention time and the type of organisms which digest the wastewater.
Retention time is much longer in an oxidation ditch. A packaged plant usually has a retention time of two to four hours while an oxidation ditch retains the wastewater for two days. Since the D.O. is higher in the oxidation ditch than in a packaged plant, a greater variety of microorganisms live in the oxidation ditch. In contrast, packaged plants usually depend upon only a few types of microorganisms to ‘eat’ the sewage.
Ammonia Removal Oxidation ditches can be set up to remove ammonia very effectively. Wastewater can be sent through two sets of ditches, each of which has a different pH. The different pH in the two ditches creates a niche for certain microorganisms. These microorganisms are very efficient at removing B.O.D and converting ammonia to nitrates. Oxidation ditches are much more efficient at ammonia removal than packaged plants.
The only pretreatment typically used in an oxidation ditch system is the bar screen. After passing through the bar screen, wastewater flows directly into the oxidation ditch.
The oxidation ditch is a circular basin through which the wastewater flows. Activated sludge is added to the oxidation ditch so that the microorganisms will digest the B.O.D. in the water. This mixture of raw wastewater and returned sludge is known as mixed liquor.
Oxygen is added to the mixed liquor in the oxidation ditch using rotating biological contactors (RBC's.) RBC's are more efficient than the aerators used in packaged plants. In addition to increasing the water's dissolved oxygen, RBC's also increase surface area and create waves and movement within the ditches. Once the B.O.D. has been removed from the wastewater, the mixed liquor flows out of the oxidation ditch. Sludge is removed in the clarifier. This sludge is pumped to an aerobic digester where the sludge is thickened with the help of aerator pumps. This method greatly reduces the amount of sludge produced. Some of the sludge is returned to the oxidation ditch while the rest of the sludge is sent to waste.
Comparison to a Packaged Plant
The treatment of wastewater in an oxidation ditch is similar to treatment in a packaged plant. The two main differences between the processes are the retention time and the type of organisms which digest the wastewater.
Retention time is much longer in an oxidation ditch. A packaged plant usually has a retention time of two to four hours while an oxidation ditch retains the wastewater for two days. Since the D.O. is higher in the oxidation ditch than in a packaged plant, a greater variety of microorganisms live in the oxidation ditch. In contrast, packaged plants usually depend upon only a few types of microorganisms to ‘eat’ the sewage.
Ammonia Removal Oxidation ditches can be set up to remove ammonia very effectively. Wastewater can be sent through two sets of ditches, each of which has a different pH. The different pH in the two ditches creates a niche for certain microorganisms. These microorganisms are very efficient at removing B.O.D and converting ammonia to nitrates. Oxidation ditches are much more efficient at ammonia removal than packaged plants.
Dissolved Air Flotation (D.A.F)
Flotation process (sometimes called flotation separation) is a method of separation widely used in the wastewater treatment and mineral processing industries.
Various flotation processes include the following:
§ Dissolved air flotation
§ Induced gas flotation
§ Froth flotation, typical in the mineral processing industry.
Dissolved air flotation (DAF) is a water treatment process that clarifies wastewaters (or other waters) by the removal of suspended matter such as oil or solids. The removal is achieved by dissolving air in the water or wastewater under pressure and then releasing the air at atmospheric pressure in a flotation tank or basin. The released air forms tiny bubbles which adhere to the suspended matter causing the suspended matter to float to the surface of the water where it may then be removed by a skimming device. (1). (2), (3).
Dissolved air flotation is very widely used in treating the industrial wastewater effluents from oil refineries, petrochemical and chemical plants, natural gas processing plants, paper mills, general water treatment and similar industrial facilities. A very similar process known as induced gas flotation is also used for wastewater treatment. Froth flotation is commonly used in the processing of mineral ores.
In the oil industry, dissolved gas flotation (DGF) units do not use air as the flotation medium due to the explosion risk. Natural gas is used instead to create the bubbles.
The feed water to the DAF float tank is often (but not always) dosed with a coagulant (such as ferric chloride or aluminum sulfate) to flocculate the suspended matter.
A portion of the clarified effluent water leaving the DAF tank is pumped into a small pressure vessel (called the air drum) into which compressed air is also introduced. This results in saturating the pressurized effluent water with air. The air-saturated water stream is recycled to the front of the float tank and flows through a pressure reduction valve just as it enters the front of the float tank, which results in the air being released in the form of tiny bubbles.
Various flotation processes include the following:
§ Dissolved air flotation
§ Induced gas flotation
§ Froth flotation, typical in the mineral processing industry.
Dissolved air flotation (DAF) is a water treatment process that clarifies wastewaters (or other waters) by the removal of suspended matter such as oil or solids. The removal is achieved by dissolving air in the water or wastewater under pressure and then releasing the air at atmospheric pressure in a flotation tank or basin. The released air forms tiny bubbles which adhere to the suspended matter causing the suspended matter to float to the surface of the water where it may then be removed by a skimming device. (1). (2), (3).
Dissolved air flotation is very widely used in treating the industrial wastewater effluents from oil refineries, petrochemical and chemical plants, natural gas processing plants, paper mills, general water treatment and similar industrial facilities. A very similar process known as induced gas flotation is also used for wastewater treatment. Froth flotation is commonly used in the processing of mineral ores.
In the oil industry, dissolved gas flotation (DGF) units do not use air as the flotation medium due to the explosion risk. Natural gas is used instead to create the bubbles.
Reference:
1. Beychok,
Milton R. (1967). Aqueous Wastes from Petroleum and Petrochemical Plants (1st ed.).
John Wiley & Sons. LCCN 67019834.
2. Lawrence
3. Kiuru, H.; Vahala, R., eds (2000). "Dissolved air flotation
in water and waste water treatment". International conference on DAF in water and
waste water treatment No. 4, Helsinki, Finland. IWA Publishing, London
A portion of the clarified effluent water leaving the DAF tank is pumped into a small pressure vessel (called the air drum) into which compressed air is also introduced. This results in saturating the pressurized effluent water with air. The air-saturated water stream is recycled to the front of the float tank and flows through a pressure reduction valve just as it enters the front of the float tank, which results in the air being released in the form of tiny bubbles.
The bubbles adhere to the suspended matter, causing the suspended matter to float to the surface and form a froth layer which is then removed by a skimmer. The froth-free water exits the float tank as the clarified effluent from the DAF unit.
Reference:(Beychok, Milton R.
(1967). Aqueous Wastes from Petroleum and Petrochemical Plants (1st ed.).
John Wiley & Sons. LCCN 67019834)
Some DAF unit designs utilize parallel plate packing material, lamellas, to provide more separation surface and therefore to enhance the separation efficiency of the unit. DAF can be categorized by Circular (more efficient) and Rectangular (more residence time). The former type requires just 3 minutes and the example is Wockoliver DAF system, whereas Rectangular requires 20 to 30 minutes the typical example can be syskill DAF system. One of the bigger advantage of Circular is its Spiral Scoop.
Operating Principle
Air under pressure is dissolved into water according to Henry's Law of Dissolution. Releasing the pressure back to STP via a special device creates millions of microbubbles approximately 30-100 microns in diameter. The microbubbles attach to floc in the water and float it to the surface for removal.
Features
High Loading - Rates 4-6 gpm/sf.
Reduced Chemical Comsumption - Formation of a large, rapidly settling floc is not required, saving money.
High Sludge Concentrations - Dewatering can occur without additional thickening, eliminating expensive sludge thickeners.
Rapid Start-Up - Good-quality water can be produced within 45 minutes of start-up.
Compact Design - Requires less space than conventional processes.
Attached growth; - trickling filter
A trickling filter consists of a fixed bed of rocks, lava, coke, gravel, slag, polyurethane foam, sphagnum peat moss, ceramic, or plastic media over which sewage or other wastewater flows downward and causes a layer of microbial slime (bio-film) to grow, covering the bed of media. Aerobic conditions are maintained by splashing, diffusion, and either by forced air flowing through the bed or natural convection of air if the filter medium is porous. The terms trickle filter, trickling biofilter, biofilter, biological filter and biological trickling filter are often used to refer to a trickling filter. These systems have also been described as roughing filters, intermittent filters, packed media bed filters, alternative septic systems, percolating filters, attached growth processes, and fixed film processes.
Onsite sewage facilities (OSSF) are recognized as viable, low-cost, long-term, decentralized approaches to sewage treatment if they are planned, designed, installed, operated and maintained properly (USEPA, 1997).
Sewage trickling filters are used in areas not serviced by municipal wastewater treatment plants (WWTP). They are typically installed in areas where the traditional septic tank system are failing, cannot be installed due to site limitations, or where improved levels of treatment are required for environmental benefits such as preventing contamination of ground water or surface water.
Sites with a high water table, high bedrock, heavy clay, small land area, or which require minimal site destruction (for example, tree removal) are ideally suited for trickling filters.
All varieties of sewage trickling filters have a low and sometimes intermittent power consumption. They can be somewhat more expensive than traditional septic tank-leach field systems, however their use allows for better treatment, a reduction in size of disposal area, less excavation, and higher density land development.
Industrial wastewater treatment trickle filters
Wastewaters from a variety of industrial processes have been treated in trickling filters. Such industrial wastewater trickling filters consist of two types:
Large tanks or concrete enclosures filled with plastic packing or other media.[1]
Vertical towers filled with plastic packing or other media.[2][3]
The availability of inexpensive plastic tower packings has led to their use as trickling filter beds in tall towers, some as high as 20 meters.[4] As early as the 1960s, such towers were in use at: the Great Northern Oil's Pine Bend Refinery in Minnesota; the Cities Service Oil Company Trafalgar Refinery in Oakville, Ontario and at a kraft paper mill.[5]
The treated water effluent from industrial wastewater trickling filters is very often subsequently processed in a clarifier-settler to remove the sludge that sloughs off the microbial slime layer attached to the trickling filter media (see Image 1 above).
Currently, some of the latest trickle filter technology involves aerated biofilters which are essentially trickle filters consisting of plastic media in vessels using blowers to inject air at the bottom of the vessels, with either downflow or upflow of the wastewater.[6]
References
General : Trickling filter wastewater treatment systems were once used primarily for secondary biological treatment. Since typical effluent characteristics do not meet today's strict effluent limitations, many systems have concerted to activated sludge. Attached growth systems still have application today when coupled with a suspended growth option.
Advantages of TF Systems : (a) simplicity of operation, (b) resistance to shock loads, (c) low sludge yield and (d) low power requirements.
Disadvantages of TF Systems : (a) relatively low BOD removal (85%), (b) high suspended solids in the effluent (20 - 30 mg/L) and (c) little operational control.
Standard Rate and High Rate Trickling Filter : Classification of trickling filters is usually based on organic and hydraulic loadings. Standard rate filters see a hydraulic loading of 25 - 100 gpd/ft2 and an organic loading of 15 - 30 lbs BOD/day/1,000 ft3. Loading greater than this will put the filter into the high rate category. Generally the higher the loading the lower the treatment (lower BOD removal). The higher the organic loading the faster the biomass growth to a point. Nitrification usually occurs in the standard rate system.
Synthetic Media : Synthetic media in a trickling filter system results in a greater surface area available for biological growth per cubic foot of filter volume. Because of the low weight of synthetic media, filters can be built 40 ft and higher. The result is the ability to handle greater loadings.
High Void Ratio : Void ratio refers to the physical openings in the media for water and solids to pass. A higher void ratio allows for a greater hydraulic loading and makes the media less susceptible to plugging.
Oxygen Transfer and Detention Time : The design of synthetic media (especially crossflow) provides for greater turbulence at the surface of the media. This greater turbulence promotes oxygen transfer. The greater the surface are per cubic foot of media, the longer it takes for the water to "trickle" through the filter. Synthetic media with 25 - 75 ft2/ft3 provide long detention times.
Objectives of Trickling Filter Recirculation : (a) reduce strength of filter influent, (b) maintain constant wetting rate, (c) force sloughing to occur, increase shear forces, (d) dilute toxic wastes, (e) reseed the filter and (f) increase air flow. Series and Parallel Flow : Parallel flow of a two-stage trickling filter system provides the greatest surface are in the first step of treatment. Parallel flow for high hydraulic and/or organic loadings. Series flow buys more treatment time. Shift to series for nitrification.
Nitrification in Trickling Filters: Nitrification occurs under the same environmental conditions as activated sludge treatment systems. Low hydraulic loadings (standard rate), warm temperatures and long detention times (series flow or synthetic media) promote nitrification. In trickling filter systems, the SBOD must be less than 20 mg/L for nitrification to occur.
Phosphorus Removal: Some of the soluble phosphorus is removed when the BOD is removed by the biomass. Additional phosphorus removal would have to take place in a separate tank. Either chemical precipitation or a suspended growth system with an anaerobic tank would be needed.
SBOD: Soluble BOD is usually the test of choice for operational control of any attached growth treatment system. To get a true measure of the BOD removal, the particulate material (sloughed biomass) must be removed from the sample. SBOD measures the dissolved organics that need to be removed by the biomass.
Combination Systems : Combination systems such as TF/SC, TF/AS, and filtration systems are used to clean up the effluent from the attached growth system. This takes advantage of the trickling filter's capability but still provides final effluent to meet a 10/10 effluent permit.
Suspended Growth vs. Attached Growth Septic Systems: Oxygen-supported (aerobic) bacteria in the mixed liquor perform the primary treatment in the system. As the bacteria themselves die off they remain suspended in the mixed liquor - a "suspended growth aerobic treatment system". Alternatively, a media, such as synthetic fabrics, may be suspended in the treatment tank, permitting the bacteria to attach to the media surfaces - an "attached growth aerobic treatment system". Saturated vs. Non-Saturated Wastewater Treatment Systems: An aerobic treatment unit (ATU), because it involves a tank filled with wastewater and forced oxygenation of that wastewater, is a type of saturated wastewater treatment system. Other non-saturated wastewater treatment systems such as trickling filter beds use passively-infused air to support their oxygen-supported microorganisms. Unlike ATUs, non-saturated systems allow passive air contact with effluent as it moves through the media. Air is not being pumped. Both types of systems make use of aerobic microorganisms.
Suspended growth;
Aeration tank
How Do Aerobic Treatment Units Work?
By bubbling compressed air through liquid effluent in a tank, ATUs create a highly oxygenated (aerobic) environment for bacteria, which uses the organic matter as an energy source. In another stage bacteria and solids settle out of the wastewater and the cleaner effluent is distributed to a soil treatment system. ATUs are more complicated than septic tanks. In a septic tank, solids are constantly separating from liquid. As individual bacterial cells grow, they sink to the bottom, along with less decomposed solids, to form a layer of sludge. Floating materials, such as fats and toilet paper, form a scum layer at the top of the tank.
· Low production of biological sludge.
· High treatment efficiency, up to 90% COD removal.
· Low capital cost, the reactor is essentially a tank.
· No oxygen requirement, hence low power consumption.
· Methane production is a potential source of fuel.
· Low nutrient requirement.
· Low operating costs
Disadvantage of the Anaerobic Process
Sensitive to temperature of influent, works best at about 35 - 40 deg C
· Sensitive to pH, works best at 6.5 – 7.8.
· Treatment efficiency diminishes as the influent COD reduces.
· Does not completely eliminate COD. Requires a secondary process.
· Methane gas may be a liability if no user available.
Solubility of metals hydroxides vs pH The solubility of the hydroxide precipitation is too high, pollution residues after this treatment is much too high. Another disadvantage with the method is the fact that that the solubility of metal hydroxide strongly depends on pH. Different metal hydroxides show solubility minima at different pH-values (see diagram). This implies that an efficient precipitation of a single metal can only be achieved in a very narrow pH-range. This makes precipitation more difficult especially in the presence of complexers such as EDTA, acid wine or lemon acid in waste water. For heavy metal water of various composition this demands multistage precipitation leading to high costs. Hydroxide precipitations of this kind are often gelatinous and difficult to remove by filters. Hydroxide precipitation is therefore often combined with ion changers, reversed osmosis, or electro- dialyse. Processes of this kind, however, are linked with high investment costs. Furthermore they do not manage major load variations.
1.
King Fahd University of Petroleum and Minerals, Course
ChE 101.11 Saudi
Aramco Engineering Development Program, pages 62-65 including Figure 11
2.
Biological filter and process U.S.
3.
Lecture by
Dr. Allen Davis, Auburn University, page 6 of 8 pdf pages
including schematic of packed tower trickling filter)
4. Beychok, Milton R. (1967). Aqueous Wastes from Petroleum and Petrochemical Plants (1st
Edition ed.). John Wiley & Sons Ltd. LCCN
67019834.
5. E.H.
Bryan and D.H. Moeller, Aerobic
Biological Oxidation Using Dowpac, Paper 42, Conference on Biological Waste
Treatment, Manhattan College, April 20, 1960. [1] ^ Marcus Van Sperling (2007). Activated Sludge and
Aerobic Biofilm Reactors. IWA Publications. ISBN 1-84339-165-1.
Advantages of TF Systems : (a) simplicity of operation, (b) resistance to shock loads, (c) low sludge yield and (d) low power requirements.
Standard Rate and High Rate Trickling Filter : Classification of trickling filters is usually based on organic and hydraulic loadings. Standard rate filters see a hydraulic loading of 25 - 100 gpd/ft2 and an organic loading of 15 - 30 lbs BOD/day/1,000 ft3. Loading greater than this will put the filter into the high rate category. Generally the higher the loading the lower the treatment (lower BOD removal). The higher the organic loading the faster the biomass growth to a point. Nitrification usually occurs in the standard rate system.
Synthetic Media : Synthetic media in a trickling filter system results in a greater surface area available for biological growth per cubic foot of filter volume. Because of the low weight of synthetic media, filters can be built 40 ft and higher. The result is the ability to handle greater loadings.
High Void Ratio : Void ratio refers to the physical openings in the media for water and solids to pass. A higher void ratio allows for a greater hydraulic loading and makes the media less susceptible to plugging.
Oxygen Transfer and Detention Time : The design of synthetic media (especially crossflow) provides for greater turbulence at the surface of the media. This greater turbulence promotes oxygen transfer. The greater the surface are per cubic foot of media, the longer it takes for the water to "trickle" through the filter. Synthetic media with 25 - 75 ft2/ft3 provide long detention times.
Objectives of Trickling Filter Recirculation : (a) reduce strength of filter influent, (b) maintain constant wetting rate, (c) force sloughing to occur, increase shear forces, (d) dilute toxic wastes, (e) reseed the filter and (f) increase air flow. Series and Parallel Flow : Parallel flow of a two-stage trickling filter system provides the greatest surface are in the first step of treatment. Parallel flow for high hydraulic and/or organic loadings. Series flow buys more treatment time. Shift to series for nitrification.
Nitrification in Trickling Filters: Nitrification occurs under the same environmental conditions as activated sludge treatment systems. Low hydraulic loadings (standard rate), warm temperatures and long detention times (series flow or synthetic media) promote nitrification. In trickling filter systems, the SBOD must be less than 20 mg/L for nitrification to occur.
Phosphorus Removal: Some of the soluble phosphorus is removed when the BOD is removed by the biomass. Additional phosphorus removal would have to take place in a separate tank. Either chemical precipitation or a suspended growth system with an anaerobic tank would be needed.
SBOD: Soluble BOD is usually the test of choice for operational control of any attached growth treatment system. To get a true measure of the BOD removal, the particulate material (sloughed biomass) must be removed from the sample. SBOD measures the dissolved organics that need to be removed by the biomass.
Combination Systems : Combination systems such as TF/SC, TF/AS, and filtration systems are used to clean up the effluent from the attached growth system. This takes advantage of the trickling filter's capability but still provides final effluent to meet a 10/10 effluent permit.
Suspended Growth vs. Attached Growth Septic Systems: Oxygen-supported (aerobic) bacteria in the mixed liquor perform the primary treatment in the system. As the bacteria themselves die off they remain suspended in the mixed liquor - a "suspended growth aerobic treatment system". Alternatively, a media, such as synthetic fabrics, may be suspended in the treatment tank, permitting the bacteria to attach to the media surfaces - an "attached growth aerobic treatment system". Saturated vs. Non-Saturated Wastewater Treatment Systems: An aerobic treatment unit (ATU), because it involves a tank filled with wastewater and forced oxygenation of that wastewater, is a type of saturated wastewater treatment system. Other non-saturated wastewater treatment systems such as trickling filter beds use passively-infused air to support their oxygen-supported microorganisms. Unlike ATUs, non-saturated systems allow passive air contact with effluent as it moves through the media. Air is not being pumped. Both types of systems make use of aerobic microorganisms.
Aeration tank
How Do Aerobic Treatment Units Work?
By bubbling compressed air through liquid effluent in a tank, ATUs create a highly oxygenated (aerobic) environment for bacteria, which uses the organic matter as an energy source. In another stage bacteria and solids settle out of the wastewater and the cleaner effluent is distributed to a soil treatment system. ATUs are more complicated than septic tanks. In a septic tank, solids are constantly separating from liquid. As individual bacterial cells grow, they sink to the bottom, along with less decomposed solids, to form a layer of sludge. Floating materials, such as fats and toilet paper, form a scum layer at the top of the tank.
In an ATU, the bubbler agitates the water so solids cannot settle out, and floating materials stay mixed in the liquid. Well-designed ATUs allow time and space for settling, while providing oxygen to the bacteria and mixing the bacteria and its food source (sewage). Any settled bacteria must be returned to the aerobic portion of the tank for mixing and treatment.
There are three basic ATU operation styles: suspended growth, fixed-film reactor, and sequencing batch reactor. All three types usually have a septic tank (sometimes called a trash tank) ahead of them that removes the large solids and provides some protection to the ATU.
A suspended-growth tank has a main treatment chamber where bacteria are free-floating and air is bubbled through the liquid. The second chamber where the solids settle out is separated from the main tank by a wall or baffle. The two chambers are connected at the bottom or by a pump, and settled bacteria from the second chamber are brought back into the main treatment chamber. This return and mixing is critical for proper operation. Treated effluent from the second chamber is piped to the soil treatment system. Though simple, the system is likely to have problems with bulking (the formation of chains or colonies of bacteria that don't settle or sink to the bottom as they should). Bulking is caused by changes in wastewater strength or quantity. When too much water/wastewater is added to the system, the bacteria can run out of food or become overloaded. Bulked bacteria remain suspended in the liquid and can clog the outflow. A fixed-film reactor has bacteria growing on a specific surface medium and air is provided to that part of the tank. The bacteria can grow on any surface including fabric, plastic, styrofoam, and gravel. Decomposition is limited to this area, and settling occurs in a second chamber. This design is expensive, but the effluent is of consistently high quality, and bulking is uncommon. There is no need for a return mechanism because the bacteria stay on the film.
There are three basic ATU operation styles: suspended growth, fixed-film reactor, and sequencing batch reactor. All three types usually have a septic tank (sometimes called a trash tank) ahead of them that removes the large solids and provides some protection to the ATU.
A suspended-growth tank has a main treatment chamber where bacteria are free-floating and air is bubbled through the liquid. The second chamber where the solids settle out is separated from the main tank by a wall or baffle. The two chambers are connected at the bottom or by a pump, and settled bacteria from the second chamber are brought back into the main treatment chamber. This return and mixing is critical for proper operation. Treated effluent from the second chamber is piped to the soil treatment system. Though simple, the system is likely to have problems with bulking (the formation of chains or colonies of bacteria that don't settle or sink to the bottom as they should). Bulking is caused by changes in wastewater strength or quantity. When too much water/wastewater is added to the system, the bacteria can run out of food or become overloaded. Bulked bacteria remain suspended in the liquid and can clog the outflow. A fixed-film reactor has bacteria growing on a specific surface medium and air is provided to that part of the tank. The bacteria can grow on any surface including fabric, plastic, styrofoam, and gravel. Decomposition is limited to this area, and settling occurs in a second chamber. This design is expensive, but the effluent is of consistently high quality, and bulking is uncommon. There is no need for a return mechanism because the bacteria stay on the film.
Sequential Batch Reactor (SBR)
In a sequencing batch reactor, aerobic decomposition, settling, and return occur in the same chamber. Air is bubbled through the liquid during the decomposition cycle. The bubbler shuts off, and the wastewater goes through a settling cycle. Once the bubbler turns back on, the tank re-enters the decomposition cycle, and settled bacteria mixes back into the aerobic environment.
After settling of bacteria and solids, the treated effluent is discharged to the soil treatment system. Bacteria settle out more consistently in this kind of tank, but since it has more moving parts and requires a controller, it has more potential for mechanical and electrical failure.
Sludge Volume Index (SVI) is a very important indicator that determines your control or rate of desludging on how much sludge is to be returned to the aeration basin and how much to take it out from the system. It actually serves as a very important empirical measurement that can be used as a guide to maintain sufficient concentration of activated sludge in the aeration basin whereby too much or too little can be considered detrimental to the system’s overall health. To put it in a lay man’s term, desludging or sometimes referred to as recycling sludge process, actually plays a very important role because the whole operation is needed to somehow strike a balance between removing dead or aged bacteria out of the systems or to determine how much goes back to the aeration pond.
SVI can actually be determined through use of standard laboratory test methods to come up with the results. Basically the procedure involves measuring the Mixed Liquor Suspended Solids (MLSS) value and also the sludge settling rate. A simple explanation on how it is carried out can be summarized below with accompanying images for easy reference and better understanding:
Obtain sample of mixed liquor from the pond discharge pipeline and fill it to a 1 liter graduated measuring cylinder until the 1.0 liter marking.
Allow it to settle for 30 minutes
After the time period, read the marking to determine the volume occupied by the settled sludge and the reading is expressed in terms of mL/L and this is figure is known as the SV value.
Next, for MLSS, there are actually two approaches to get the value. A conventional standard approach is by filtering the sludge, drying it and then weigh the second portion of the mixed liquid. However, this can be time consuming and a faster way is by using MLSS meter. Value of Sludge Volume Index can then be calculated from the formula given here. Whereby,
SVI = SV/MLVSS X 1000
SVI = Sludge Volume Index, mL/g
SV = Volume of settled solids in one-liter graduated transparent measuring cylinder after 30 minutes settling period, mL/L
MLSS = Mixed liquor Suspended Solids, ppm
SVI is a key factor when it comes to the clarifier design so that a clear wastewater discharge can be obtained without significant carry over of sludge. Basically what the value represents is the settling characteristics that have profound effect on the return rates and also the MLSS value. Typically a healthy sludge aeration pond basin should have the value registered within 80 to 150 mL/g and the MLSS concentration between 3000 – 5000ppm with the wastewater temperature less than 20degC. With this value in mind, generally the clarifier or settling basin has to be designed to accept higher solid loadings so that loss or carry over of sludge due to hydraulic displacement can be minimized.
Activated sludge pond is designed to allow adjustments on the amount of sludge return and also the take off rate. Regular desludging must be carried out to remove the aged sludge so that the new bacteria can regenerate and allowed to grow. As an experienced operator or engineers that operate the wastewater treatment plant, a tight control must be put in place to adjust the MLSS value to the desired concentration based on the set limit SVI to be used as a guide.
Anaerobic digestion
Principles & application
Anaerobic digestion
Technical Description Many people are concerned about pollution and the management of waste, but for some industries, this problem can become overwhelming. For example how do farmers deal with inevitable daily replenishing of methane-producing manure piles? How do palm-oil millers dispose of large amounts of oily organic wastewater? For these kinds of companies, anaerobic digestion is the best waste management option. Anaerobic digestion transforms waste into useful end-products, removing dangerous pollutants in the process.
Anaerobic wastewater treatment is a process whereby bacteria digests biosolids in the absence of oxygen. One major feature of anaerobic digestion is the production of biogas, which can be used in generators for electricity production or in boilers for heating purposes. This, plus the fact that aerobic wastewater treatment requires a method for the introduction of oxygen into the process, makes anaerobic wastewater treatment generally more cost effective.In a sequencing batch reactor, aerobic decomposition, settling, and return occur in the same chamber. Air is bubbled through the liquid during the decomposition cycle. The bubbler shuts off, and the wastewater goes through a settling cycle. Once the bubbler turns back on, the tank re-enters the decomposition cycle, and settled bacteria mixes back into the aerobic environment.
Sludge Volume Index (SVI) is a very important indicator that determines your control or rate of desludging on how much sludge is to be returned to the aeration basin and how much to take it out from the system. It actually serves as a very important empirical measurement that can be used as a guide to maintain sufficient concentration of activated sludge in the aeration basin whereby too much or too little can be considered detrimental to the system’s overall health. To put it in a lay man’s term, desludging or sometimes referred to as recycling sludge process, actually plays a very important role because the whole operation is needed to somehow strike a balance between removing dead or aged bacteria out of the systems or to determine how much goes back to the aeration pond.
SVI can actually be determined through use of standard laboratory test methods to come up with the results. Basically the procedure involves measuring the Mixed Liquor Suspended Solids (MLSS) value and also the sludge settling rate. A simple explanation on how it is carried out can be summarized below with accompanying images for easy reference and better understanding:
Obtain sample of mixed liquor from the pond discharge pipeline and fill it to a 1 liter graduated measuring cylinder until the 1.0 liter marking.
Allow it to settle for 30 minutes
After the time period, read the marking to determine the volume occupied by the settled sludge and the reading is expressed in terms of mL/L and this is figure is known as the SV value.
Next, for MLSS, there are actually two approaches to get the value. A conventional standard approach is by filtering the sludge, drying it and then weigh the second portion of the mixed liquid. However, this can be time consuming and a faster way is by using MLSS meter. Value of Sludge Volume Index can then be calculated from the formula given here. Whereby,
SVI = SV/MLVSS X 1000
SVI = Sludge Volume Index, mL/g
SV = Volume of settled solids in one-liter graduated transparent measuring cylinder after 30 minutes settling period, mL/L
MLSS = Mixed liquor Suspended Solids, ppm
SVI is a key factor when it comes to the clarifier design so that a clear wastewater discharge can be obtained without significant carry over of sludge. Basically what the value represents is the settling characteristics that have profound effect on the return rates and also the MLSS value. Typically a healthy sludge aeration pond basin should have the value registered within 80 to 150 mL/g and the MLSS concentration between 3000 – 5000ppm with the wastewater temperature less than 20degC. With this value in mind, generally the clarifier or settling basin has to be designed to accept higher solid loadings so that loss or carry over of sludge due to hydraulic displacement can be minimized.
Activated sludge pond is designed to allow adjustments on the amount of sludge return and also the take off rate. Regular desludging must be carried out to remove the aged sludge so that the new bacteria can regenerate and allowed to grow. As an experienced operator or engineers that operate the wastewater treatment plant, a tight control must be put in place to adjust the MLSS value to the desired concentration based on the set limit SVI to be used as a guide.
Principles & application
Technical Description Many people are concerned about pollution and the management of waste, but for some industries, this problem can become overwhelming. For example how do farmers deal with inevitable daily replenishing of methane-producing manure piles? How do palm-oil millers dispose of large amounts of oily organic wastewater? For these kinds of companies, anaerobic digestion is the best waste management option. Anaerobic digestion transforms waste into useful end-products, removing dangerous pollutants in the process.
What is Anaerobic Digestion?
Anaerobic digestion is a process by which certain kinds of bacteria break down biodegradable material in the absence of oxygen. This useful biological process is often used for waste management. Organic wastes are collected in a tank sealed off from oxygen, and anaerobic bacteria are added, resulting in useful end products including fertilizer and methane-based biofuel.
Bacteria Involved
Acetogens break down organic material to form acetic acid.
Methanogens break down organic material to form methane.
Stages of the Process
1. Hydrolysis
During this stage, carbohydrates, fats and proteins are broken down into sugars, fatty acids and amino acids respectively. This process involves the conversion of impurities into a form that is readily attacked by bacteria. The high molecular substances (polymers, carbohydrates, fats), un-dissolved substances and proteins are disintegrated. These substances are transformed into fragments by means of enzymes secreted by bacteria.
2. Acidogenisis
Next, these sugars, fatty acids and amino acids are broken down to form carbonic acids, alcohols, hydrogen, carbon dioxide and ammonia. This process is similar to fermentation. The dissolved fragments are consumed by fermenting bacteria. In this stage, there is some odour created due to the fermentation process, mainly due to the formation of butric acid, propionic acid, valeric acid etc, but also alcohol if there are carbohydrates in the effluent. The byproducts of the process are hydrogen and carbon dioxide.
3. Acetogenisis
The products of the above reactions are further converted to produce more hydrogen and carbon dioxide, along with acetic acid. During this phase, the organic acids and alcohol are transformed to acetic acid. The by-product of this process is hydrogen. This reaction cannot run independently. A positive energy balance can only be reached within a certain range of hydrogen partial-pressures. Thus the acetic phase is dependent on a hydrogen consuming microbiological population.
4. Methanogenis
Methanogens convert products from the intermediate processes into methane, carbon dioxide and water. The acetic acid is broken down into carbon dioxide and methane. The reaction is pH and temperature sensitive. The pH range for effective methane conversion is pH 6.5 – 7.6. The reaction is best managed at a mesophylic temperature range of 35 – 37 degrees C.
IMPORTANT: Although this is a natural process, there are many factors that must be carefully controlled. DO NOT attempt to create an anaerobic digestion system without the advice or supervision of an expert. Resultant products include dangerous acids and gases, and temperature and pressure must be tracked to ensure the safety and effectiveness of any system.
What kinds of wastes can undergo anaerobic digestion?
Anaerobic bacteria can feed on a variety of materials, making anaerobic digestion an attractive waste management strategy for many different industries. Among the most common types of wastes used in anaerobic digestion facilities:
· food wastes and residues
· farm manure
· waste water from food production
· grease trap fat
· specially grown raw material meant for the production of biogas.
What are the products of anaerobic digestion?
The products of anaerobic digestion are truly the golden egg of the process. Many of these facilities are expensive to install in maintain, but once they've been built, they can transform wastes and pollutants into revenue-creating natural gas and fertilizers. The three main products of the process are:
· Methane biogas
· Solid fibrous material, which can improve soil structure and fertility Nutrient rich liquid, which can be used as a fertilizer.
Anaerobic digestion is a process by which certain kinds of bacteria break down biodegradable material in the absence of oxygen. This useful biological process is often used for waste management. Organic wastes are collected in a tank sealed off from oxygen, and anaerobic bacteria are added, resulting in useful end products including fertilizer and methane-based biofuel.
Bacteria Involved
Acetogens break down organic material to form acetic acid.
Methanogens break down organic material to form methane.
Stages of the Process
1. Hydrolysis
During this stage, carbohydrates, fats and proteins are broken down into sugars, fatty acids and amino acids respectively. This process involves the conversion of impurities into a form that is readily attacked by bacteria. The high molecular substances (polymers, carbohydrates, fats), un-dissolved substances and proteins are disintegrated. These substances are transformed into fragments by means of enzymes secreted by bacteria.
2. Acidogenisis
Next, these sugars, fatty acids and amino acids are broken down to form carbonic acids, alcohols, hydrogen, carbon dioxide and ammonia. This process is similar to fermentation. The dissolved fragments are consumed by fermenting bacteria. In this stage, there is some odour created due to the fermentation process, mainly due to the formation of butric acid, propionic acid, valeric acid etc, but also alcohol if there are carbohydrates in the effluent. The byproducts of the process are hydrogen and carbon dioxide.
3. Acetogenisis
The products of the above reactions are further converted to produce more hydrogen and carbon dioxide, along with acetic acid. During this phase, the organic acids and alcohol are transformed to acetic acid. The by-product of this process is hydrogen. This reaction cannot run independently. A positive energy balance can only be reached within a certain range of hydrogen partial-pressures. Thus the acetic phase is dependent on a hydrogen consuming microbiological population.
4. Methanogenis
Methanogens convert products from the intermediate processes into methane, carbon dioxide and water. The acetic acid is broken down into carbon dioxide and methane. The reaction is pH and temperature sensitive. The pH range for effective methane conversion is pH 6.5 – 7.6. The reaction is best managed at a mesophylic temperature range of 35 – 37 degrees C.
IMPORTANT: Although this is a natural process, there are many factors that must be carefully controlled. DO NOT attempt to create an anaerobic digestion system without the advice or supervision of an expert. Resultant products include dangerous acids and gases, and temperature and pressure must be tracked to ensure the safety and effectiveness of any system.
What kinds of wastes can undergo anaerobic digestion?
Anaerobic bacteria can feed on a variety of materials, making anaerobic digestion an attractive waste management strategy for many different industries. Among the most common types of wastes used in anaerobic digestion facilities:
· food wastes and residues
· farm manure
· waste water from food production
· grease trap fat
· specially grown raw material meant for the production of biogas.
The products of anaerobic digestion are truly the golden egg of the process. Many of these facilities are expensive to install in maintain, but once they've been built, they can transform wastes and pollutants into revenue-creating natural gas and fertilizers. The three main products of the process are:
· Methane biogas
· Solid fibrous material, which can improve soil structure and fertility Nutrient rich liquid, which can be used as a fertilizer.
Aerobic versus Anaerobic – the ‘Carbon Concern’
Advantage of the Anaerobic Processes · Low production of biological sludge.
· High treatment efficiency, up to 90% COD removal.
· Low capital cost, the reactor is essentially a tank.
· No oxygen requirement, hence low power consumption.
· Methane production is a potential source of fuel.
· Low nutrient requirement.
· Low operating costs
Disadvantage of the Anaerobic Process
Sensitive to temperature of influent, works best at about 35 - 40 deg C
· Sensitive to pH, works best at 6.5 – 7.8.
· Treatment efficiency diminishes as the influent COD reduces.
· Does not completely eliminate COD. Requires a secondary process.
· Methane gas may be a liability if no user available.
Chemical treatment
Coagulation
· The scheme;
· Coagulation mechanism;
Coagulation and flocculation of particles are essential pre-treatment methods for many water purification systems. It is usually done prior to any biological treatment for COD and BOD reduction in general. In conventional coagulation-flocculation-sedimentation, a coagulant is added to the source water to create an attraction among the suspended particles. The mixture is slowly stirred to induce particles to clump together into “flocs.” The water is then moved into a quiet sedimentation basin to settle out the solids. Dissolved air flotation (DAF) systems also add coagulant and flocculate the suspended particles; but instead of using sedimentation, pressurized air bubbles force them to the water surface where they can be skimmed off.
· Coagulation mechanism;
A flocculation-chlorination system has been developed as a point-of-use technology, especially for developing countries. It uses small packets of chemicals and simple equipment like buckets and a cloth filter to purify the water. Finally, lime softening is a technology typically used to “soften” water—that is, to remove calcium and magnesium mineral salts. In this case, the material that is settled out is not suspended sediment but dissolved salts.
Methods;
The principal phenomena that control the behaviour of the colloids are zeta potential (electrostatic force), Van Der Walls forces and Brownian motion. The amount of coagulant to be added to the water will depend on the zeta potential, a measurement of the magnitude of electrical charge surrounding the colloidal particles. The zeta potential is the amount of repulsive force or electric charge, which keeps the particles in the water. If the zeta potential is large, then more coagulants will be needed. Van der Waal’s forces refer to the tendency of particles in nature to attract each other weakly if they have no charge. Once the particles in water are not repelling each other, van der Waal’ s forces make the particles drift toward each other and join together into a group.
Colloids have a sufficiently small mass that collides with molecular size particles in water will cause constant movement of the colloids. The phenomenon of constant random movement of colloids is known as Brownian motion. The combination of positive and negative charge, results in a neutral, or lack of charge. As a result, the particles no longer repel each other. When enough particles have joined together, they become floc and will settle out of the water.
The chemistry of coagulation and flocculation is primarily based on electricity. Electricity is the behavior of negatively and positively charged particles due to their attraction and repulsion. Like charges (two negatively charged particles or two positively charged particles) repel each other while opposite charges (a positively charged particle and a negatively charged particle) attract. Most particles dissolved in water have negative charge, so they tend to repel each other. As a result, they stay dispersed and dissolved or Coagulation process colloidal in the water. Addition of positively charged particles in the coagulation process is aimed to destabilizing the colloids. So treatment involving coagulation and flocculation is typical of surface water.
The purpose of addition of coagulant chemicals is to neutralize the negative charges on the colloidal particles to prevent those particles from repelling each other. Coagulants due to their positive charge attract negatively charged particles in the water.
Coagulation is a unit process of addition of coagulant chemicals to water and rapid mixing so as to neutralize the electrical charges of the colloidal particles in the water, and allow them to come closer and form fine clumps or micro flocs.
Coagulation
Coagulation, the first step in complete clarification, is the neutralization of the electrostatic charges on colloidal particles. Because most of the smaller suspended solids in surface waters carry a negative electrostatic charge, the natural repulsion of these similar charges causes the particles to remain dispersed almost indefinitely. To allow these small suspended solids to agglomerate, the negative electrostatic charges must be neutralized. This is accomplished by using inorganic coagulants (water soluble inorganic compounds), organic cationic polymers or polyelectrolytes.
Flocculation - The Second Step of the Coagulation Process
Once the negative charges of the suspended solids are neutralized, flocculation begins. Charge reduction increases the occurrence of particle-particle collisions, promoting particle agglomeration. Portions of the polymer molecules not absorbed protrude for some distance into the solution and are available to react with adjacent particles, promoting flocculation. Bridging of neutralized particles can also occur when two or more turbidity particles with a polymer chain attached come together. It is important to remember that during this step, when particles are colliding and forming larger aggregates, mixing energy should be great enough to cause particle collisions but not so great as to break up these aggregates as they are formed. In some cases flocculation aids are employed to promote faster and better flocculation. These flocculation aids are normally high molecular weight anionic polymers. Flocculation aids are normally necessary for primary coagulants and water sources that form very small particles upon coagulation. A good example of this is water that is low in turbidity but high in color (colloidal suspension).
Solubility of metals as a function of pH;
The principal phenomena that control the behaviour of the colloids are zeta potential (electrostatic force), Van Der Walls forces and Brownian motion. The amount of coagulant to be added to the water will depend on the zeta potential, a measurement of the magnitude of electrical charge surrounding the colloidal particles. The zeta potential is the amount of repulsive force or electric charge, which keeps the particles in the water. If the zeta potential is large, then more coagulants will be needed. Van der Waal’s forces refer to the tendency of particles in nature to attract each other weakly if they have no charge. Once the particles in water are not repelling each other, van der Waal’ s forces make the particles drift toward each other and join together into a group.
The chemistry of coagulation and flocculation is primarily based on electricity. Electricity is the behavior of negatively and positively charged particles due to their attraction and repulsion. Like charges (two negatively charged particles or two positively charged particles) repel each other while opposite charges (a positively charged particle and a negatively charged particle) attract. Most particles dissolved in water have negative charge, so they tend to repel each other. As a result, they stay dispersed and dissolved or Coagulation process colloidal in the water. Addition of positively charged particles in the coagulation process is aimed to destabilizing the colloids. So treatment involving coagulation and flocculation is typical of surface water.
The purpose of addition of coagulant chemicals is to neutralize the negative charges on the colloidal particles to prevent those particles from repelling each other. Coagulants due to their positive charge attract negatively charged particles in the water.
Coagulation is a unit process of addition of coagulant chemicals to water and rapid mixing so as to neutralize the electrical charges of the colloidal particles in the water, and allow them to come closer and form fine clumps or micro flocs.
Coagulation
Coagulation, the first step in complete clarification, is the neutralization of the electrostatic charges on colloidal particles. Because most of the smaller suspended solids in surface waters carry a negative electrostatic charge, the natural repulsion of these similar charges causes the particles to remain dispersed almost indefinitely. To allow these small suspended solids to agglomerate, the negative electrostatic charges must be neutralized. This is accomplished by using inorganic coagulants (water soluble inorganic compounds), organic cationic polymers or polyelectrolytes.
Flocculation - The Second Step of the Coagulation Process
Once the negative charges of the suspended solids are neutralized, flocculation begins. Charge reduction increases the occurrence of particle-particle collisions, promoting particle agglomeration. Portions of the polymer molecules not absorbed protrude for some distance into the solution and are available to react with adjacent particles, promoting flocculation. Bridging of neutralized particles can also occur when two or more turbidity particles with a polymer chain attached come together. It is important to remember that during this step, when particles are colliding and forming larger aggregates, mixing energy should be great enough to cause particle collisions but not so great as to break up these aggregates as they are formed. In some cases flocculation aids are employed to promote faster and better flocculation. These flocculation aids are normally high molecular weight anionic polymers. Flocculation aids are normally necessary for primary coagulants and water sources that form very small particles upon coagulation. A good example of this is water that is low in turbidity but high in color (colloidal suspension).
Solubility of metals hydroxides vs pH The solubility of the hydroxide precipitation is too high, pollution residues after this treatment is much too high. Another disadvantage with the method is the fact that that the solubility of metal hydroxide strongly depends on pH. Different metal hydroxides show solubility minima at different pH-values (see diagram). This implies that an efficient precipitation of a single metal can only be achieved in a very narrow pH-range. This makes precipitation more difficult especially in the presence of complexers such as EDTA, acid wine or lemon acid in waste water. For heavy metal water of various composition this demands multistage precipitation leading to high costs. Hydroxide precipitations of this kind are often gelatinous and difficult to remove by filters. Hydroxide precipitation is therefore often combined with ion changers, reversed osmosis, or electro- dialyse. Processes of this kind, however, are linked with high investment costs. Furthermore they do not manage major load variations.
· Coagulation agent
Poly Aluminum Ferric Chloride (PAFC)
Preparation
Chromium reduction;
Trivalent chromium (Cr3+) is an essential mineral involved in the metabolism of glucose for energy and the synthesis of fatty acids and cholesterol. It helps to lower blood sugar, increase insulin sensitivity, reduce body fat, reduce cholesterol and triglycerides levels, and increase lean muscle mass. It also appears to increase the effectiveness of insulin and its ability to handle glucose, preventing hypoglycemia or diabetes. It as a trace mineral is found distributed in many tissues, mainly in liver, kidney and bone marrow. Trivalent Chromium is an essential component of GTF (the cofactor of insulin receptor), which works with insulin to stabilize blood sugar levels. Poor dietary intake of chromium results in limited availability of glucose tolerance factor (GTF) and impaired insulin activity. Blood sugar remains elevated and a diabetes-like condition similar to Type II Adult onset develops. In addition, strenuous labor, pregnancy, obesity, old age, alcohol abuse, surgery and infection can all cause the more excretion of GTF and lead to its deficiency.
References
http://www.livestrong.com/article/315080-side-effects-of-hexavalent-chromium/#ixzz1cmhq1oe3
Tertiary Treatment;
o Adsorption;
Activated carbon; Activated carbon is a carbon material mostly derived from charcoal. The unique structure of activated carbon produces a very large surface area: 1 lb of granular activated carbon typically provides a surface area of 125 acres (1 Kg =1,000,000 sq. m.). The activated carbon surface is non-polar which results in an affinity for non-polar adsorbates such as organics. Activated carbon is very effective in applications requiring air or water purification as well as precious metal recovery or removal.
· Its production;
· Its properties;
· Application in removing Volatile Organic Carbon (VOC)
Pore Size
Correct pore size distribution is necessary to facilitate the adsorption process by providing adsorption sites and the appropriate channels to transport the adsorbate. Activated Carbon Pores can be divided into three general sizes:
Micro-pores (diameter in the range of less than 2nm)
Meso-pores (diameter in the range of 2 – 25 nm)
- A cation exchange membrane has anion active agents, so it selectively lets positive ions pass through.
- An anion exchange membrane has cation active agents, so it electrostatically lets anions move through.
- Inflowing water is distributed to EDI cells. When the direct current electricity is supplied, cations in the water go through the cation exchange membrane toward the negative electrode while anions pass through the anion exchange membrane toward the cation electrode.
- Demineralized water is produced in the diluting chamber with the ions eliminated while ion-enriched chamber produces or circulates enriched water.
What are Ion Exchange Resins?
Ion exchange resins can be made from synthetic or natural materials shaped into grain-of-sand-sized beads. Ions are negatively or positively charged atoms or molecules. The ion exchange resins have the opposite charge of the contaminant ions they are treating. This causes contaminants in water pumped through a container of ion exchange resin to be attracted to and stick to the resin similar to the way metal reacts to a magnet. When the contaminant ion attaches to the resin, it displaces another similarly charged ion into the water being treated. That ion is "exchanged" for the contaminant.
Membrane filtration
Principles and technology;
Membrane technologies include reverse osmosis (RO), nanofiltration (NF), ultrafiltration (UF), microfiltration (MF), pervaporation (PV) and electrodialysis (ED). Two areas of special concern are membrane fouling (and cleaning) and energy consumption characteristics of various membranes and modules.
Poly Aluminum Chloride
Chemical name: PAC
Molecular formula: [Al2(OH)nCl6-n]m where;
1<m<10, n<5
PAC is composing of a
series of inorganic macromolecule compound which has different polymerization
degree, and has the best shape distributing. It’s mainly distributed into Al13O4(OH)24(H2O)24(H2O)127+. It has the Keg gin
configuration and high electricity polymeric annular chain shape, and has the
high electricity neutralization and bridging function to the colloid and grain
substance in water. It has the strong power of removing the poisonous matter
and heavy metal ion.
This product, as a kind of inorganic compound polymer,
coordinates polymeric Fe on the basis of Poly Aluminum chloride, which enlarge
molecular structure and improve the performance of charge neutrality, truss
absorption and sedimentation. It is an ideal chemical reagent for the treatment
of seriously polluted raw water, low temperature and high turbidity water, and
low temperature and low turbidity water.
Features:
1. Combining the coagulatory
advantages of Aluminum salt and Iron salt, and being able to rapidly form
flocculation with more imporosity and rapid sedimentation;
2. Suited to raw water at various
temperatures and having superiors solubility;
3. Less dosage than other Aluminum
salt water treatment chemicals and having lower cost.
Poly Electrolytes: Anionic Powders/ Cationic
Powders
Flocculants are used specially for water
treatment, oilfield, wastewater treatment, potable water, mineral processing,
sugar and paper industries.
Polyelectrolyte is a high molecular weight flocculant of polyacrylamide type. It is used as
clarification and filtration agent of river water, waste water and industrial
water. It has wide application in process treatment of mining, metal &
ceramics. Besides, it is a good clarifying agent for waste water of textile,
mining, pump & paper, steel, metal and chemicals
Aluminum Sulfate
Aluminum sulfate, written as Al2(SO4)3 or Al2O12S3,
is a widely used industrial chemical. It is sometimes incorrectly referred to
as Alum, as it is closely
related to this group of compounds. It occurs naturally as a rare mineral
millosevichite, found i.e. in volcanic environments and on burning coal-mining
waste dumps. It is frequently used as a flocculating agent in the purification
of drinking water and waste water treatment plants, and also in paper
manufacturing.
Preparation
Aluminum sulfate may be made by dissolving Aluminum Hydroxide,
Al(OH)3, in Sulfuric Acid, H2SO4:
2Al(OH)3 + 3 H2SO4 + 3 H2O → Al2(SO4)3·6H2O
The most common inorganic coagulants
are:
1. Alum-aluminum sulfate-Al2(SO4)3
2. Ferric sulfate-Fe2(SO4)3
3. Ferric chloride-FeCl3
4. Sodium aluminate-Na2AI204
Inorganic salts of metals work by two
mechanisms in water clarification. The positive charge of the metals serves to
neutralize the negative charges on the turbidity particles. The metal salts
also form insoluble metal hydroxides which are gelatinous and tend to
agglomerate the neutralized particles. The most common coagulation reactions
are as follows:
Al2(SO4)3 + 3Ca(HCO3)2 = 2Al(OH)3 + 3CaSO4 + 6CO2
Al2(SO4)3 + 3Na2CO3 + 3H2O = 2AI(OH)3 + 3Na2SO4 + 3CO2
Al2(SO4)3 + 6NaOH = 2AI(OH)3 + 3Na2SO4
Al2(SO4)3 (NH4)2SO4 + 3Ca(HC03) = 2AI(OH)3 + (NH4)2SO4
+ 3CaSO4 + 6CO2
Al2(SO4)3 K2SO4 + 3Ca(HCO3)2 = 2AI(OH)3 + K2SO4 + 3CaSO4 + 6CO2
Na2AI204 + Ca(HCO3)2 + H20 = 2AI(OH)3 + CaCO3 + Na2CO2
Fe(SO4)3 + 3Ca(OH)2 = 2Fe(OH)3 + 3CaSO4
4Fe(OH)2 + O2 + 2H2O = 4Fe(OH)3
Fe2(SO4)3 + 3Ca(HCO3) = 2Fe(OH)3 + 3CaSO4 + 6CO2
While these coagulants serve the same
function as the inorganic metal salts, the process is simpler because the
charge neutralization reaction is the only concern. Polymer addition has no
effect on pH or alkalinity, so no supplemental chemical feed is required to
control either.
Polymers can be envisioned as long
chains with molecular weights of 1000 or less to 5,000,000 or more. Along the
chain are numerous charged sites. In primary coagulants, these sites are
positively charged. The sites are available for adsorption onto the negatively
charged particles in the water. To accomplish optimum polymer dispersion and
polymer/particle contact, initial mixing intensity is critical. The mixing must
be rapid and thorough. Polymers used for charge neutralization cannot be over-diluted or over-mixed. The
farther upstream in the system these polymers can be added, the better their
performance.
Because most polymers are viscous,
they must be properly diluted before they are added to the influent water.
Special mixers such as static mixers, mixing tees and specially designed
chemical dilution and feed systems are all aids in polymer dilution.
Color
Removal
By far the most difficult impurity to
remove from most surface waters is color (from dissolved or colloidal suspensions
of decayed vegetation) and other colloidal suspensions.
Color in surface water normally is a
result of its contact with decayed vegetation and is composed of tannins and
lignins, the components that hold together the cellulose cells in vegetation.
In addition to their undesirable appearance in drinking water, these organics
can cause serious problems in downstream water purification processes. For
example:
1. Expensive demineralizer resins can
be irreversibly fouled by these materiais.
2. Some of these organics have
chelated trace metals, such as iron and manganese within their structure, which
can cause serious deposition problems in a cooling system.
There are many ways of optimizing
color removal in a clarifier:
1. Prechlorination (before the clarifier) significantly improves the removal of
organics as well as reducing the coagulant demand.
2. The proper selection of polymers for coagulation has a significant impact on organic
removal.
3. Color removal is affected by pH. Generally, organics are less soluble at low pH.
Should organic removal prove to be a
problem, a relatively simple test procedure is available to determine removal
efficiency. (Refer to Bench
Testing Procedures Handbook.)
The simplest form of clarification
uses a large tank or horizontal basin for sedimentation of flocculated solids,
as shown in Figures 6.1 and 6.2. The basin may contain separate chambers for
rapid mix, slow mix and settling. The first two steps are important for good
clarification. An initial period of turbulent mixing is necessary for contact
between the coagulant and the suspended matter, followed by a period of gentle
stirring to increase collisions between particles and increase floc size.
Typical retention times are 3-5 minutes for rapid mix, 15 to 30 minutes for
flocculation. and 4-6 hours for settling.
The coagulant is added to the waste water in the rapid mix chamber or
just upstream, and the water passes through the mix chambers into the settling
basin. As the water passes along the length of the basin (or out to the
circumference in the case of a circular clarifier), the flocculated particles
settle to the bottom and are scraped into a sludge collection basin for removal
and disposal. Clear water flows over a weir and is usually held in a tank
called a clearwell.
Aluminum salts are most effective
as coagulants in a 5.5-8.0 pH range. Because they react
with the alkalinity in the water, it may be necessary to add additional alkalinity
in the form of lime or soda ash. Iron salts, on the other hand, are most
effective as coagulants at higher pH ranges (8-10). Iron salts also depress
alkalinity and pH levels; therefore, additional alkalinity must be added.
Sodium aluminate increases the
alkalinity of water, so care must be taken not to exceed pH and alkalinity
guidelines. As is evident from the reactions discussed above, a working
knowledge of the alkalinity relationships of water is mandatory.
It is important to note, at this point, that the use of metal salts for
coagulation may increase the quantity of dissolved solids. One must consider
the downstream impact of these dissolved solids. In addition, the impact of carryover of suspended Al+++ and Fe+++ compounds and their
related effect on downstream processes must be considered. It
must also be pointed out that using inorganic
coagulants produces a voluminous, low-solids sludge that dewaters and dries
very slowly.
Cyanide destruction;
Chromium reduction;
Trivalent chromium (Cr3+) is an essential mineral involved in the metabolism of glucose for energy and the synthesis of fatty acids and cholesterol. It helps to lower blood sugar, increase insulin sensitivity, reduce body fat, reduce cholesterol and triglycerides levels, and increase lean muscle mass. It also appears to increase the effectiveness of insulin and its ability to handle glucose, preventing hypoglycemia or diabetes. It as a trace mineral is found distributed in many tissues, mainly in liver, kidney and bone marrow. Trivalent Chromium is an essential component of GTF (the cofactor of insulin receptor), which works with insulin to stabilize blood sugar levels. Poor dietary intake of chromium results in limited availability of glucose tolerance factor (GTF) and impaired insulin activity. Blood sugar remains elevated and a diabetes-like condition similar to Type II Adult onset develops. In addition, strenuous labor, pregnancy, obesity, old age, alcohol abuse, surgery and infection can all cause the more excretion of GTF and lead to its deficiency.
Step 1. Reduction process
– Sulfur dioxide, sodium bisulfite, sodium metabisulfite
– Cr(VI) à Cr(III)
– Sodium metabisulfite at pH2:
1.5Na2S2O5 + 2H2SO4 + 2H2CrO4 à Cr2(SO4)3 + Na2SO4 + NaHSO4 + 3.5H2O
Step 2. Precipitation of Cr(III)
NaOH, lime. Lime at pH 8.5 to 9:
Cr2(SO4)3 + 3Ca(OH)2 à 2Cr(OH)3 + 3CaSO4
Hexavalent chromium (Cr6+), or chromium VI, is a man-made compound containing chromium. Several occupations require hexavalent chromium use, such as steel manufacturing and welding, chromate pigments and chemicals and thermal cutting. The Centers for Disease Control and Prevention considers hexavalent chromium in any form to be a carcinogen. Small-scale exposure to hexavalent chromium will unlikely cause any side effects; however, you should avoid ingesting and minimize contact with products containing hexavalent chromium.
Skin Irritation
Prolonged or repeated exposure of hexavalent chromium to the skin or eyes can cause irritations, such as discolorations and rashes. Symptoms will progressively get worse with repeated exposure. A report published in the "Archives of Toxicology" in 1981 demonstrated the ability of hexavalent chromium to be absorbed through the skin. Prolonged exposure simply allowed hexavalent chromium to accumulate in cells and move to the blood stream to be taken throughout the body. You should take precautions to prevent exposure to hexavalent chromium in liquid form and to minimize exposure to skin and eyes when working with hexavalent chromium.
Asthma
Signs of respiratory distress have been reported in people who are exposed to industrial hexavalent chromium by-products daily. Airborne particulates can accumulate in the lungs and make breathing more difficult, according to the CDC. Moreover, nasal passages, throat and mouth may become scarred. You should wear a protective face mask in order to guard against this possibility. If you experience chronic nosebleeds, you should be evaluated for toxic hexavalent chromium exposure.
Kidney and Liver Damage
Your kidneys and liver will attempt to filter toxins from your body. Hexavalent chromium, however, accumulates in the kidneys and liver without a method to escape. This accumulation causes cellular toxicity and forces the kidney and liver cells to die. If you notice a change in urine output you may be experiencing symptoms of kidney failure. Eventually, kidney and liver failure is possible with prolonged exposure to hexavalent chromium.
Teeth Degradation
Hexavalent chromium has the ability to erode the enamel protecting your teeth. Repeated exposure of hexavalent chromium to your mouth will cause discoloration of teeth followed by erosion. The CDC has a comprehensive website that illustrates this troubling affect.
Lung Cancer
Hexavalent chromium is considered a general carcinogen. If ingested, you may experience any type of cancer, including stomach, throat and uterine cancer. Lung cancer, however, is the most prevalent form of cancer caused by hexavalent chromium. Typically, industrial workers exposed to hexavalent chromium on a daily basis develop lung cancer. Since there is not a method to definitely diagnose cancer caused uniquely by hexavalent chromium exposure, there may be other more prevalent forms of cancer not yet attributed to hexavalent chromium.
Skin Irritation
Prolonged or repeated exposure of hexavalent chromium to the skin or eyes can cause irritations, such as discolorations and rashes. Symptoms will progressively get worse with repeated exposure. A report published in the "Archives of Toxicology" in 1981 demonstrated the ability of hexavalent chromium to be absorbed through the skin. Prolonged exposure simply allowed hexavalent chromium to accumulate in cells and move to the blood stream to be taken throughout the body. You should take precautions to prevent exposure to hexavalent chromium in liquid form and to minimize exposure to skin and eyes when working with hexavalent chromium.
Asthma
Signs of respiratory distress have been reported in people who are exposed to industrial hexavalent chromium by-products daily. Airborne particulates can accumulate in the lungs and make breathing more difficult, according to the CDC. Moreover, nasal passages, throat and mouth may become scarred. You should wear a protective face mask in order to guard against this possibility. If you experience chronic nosebleeds, you should be evaluated for toxic hexavalent chromium exposure.
Kidney and Liver Damage
Your kidneys and liver will attempt to filter toxins from your body. Hexavalent chromium, however, accumulates in the kidneys and liver without a method to escape. This accumulation causes cellular toxicity and forces the kidney and liver cells to die. If you notice a change in urine output you may be experiencing symptoms of kidney failure. Eventually, kidney and liver failure is possible with prolonged exposure to hexavalent chromium.
Teeth Degradation
Hexavalent chromium has the ability to erode the enamel protecting your teeth. Repeated exposure of hexavalent chromium to your mouth will cause discoloration of teeth followed by erosion. The CDC has a comprehensive website that illustrates this troubling affect.
Lung Cancer
Hexavalent chromium is considered a general carcinogen. If ingested, you may experience any type of cancer, including stomach, throat and uterine cancer. Lung cancer, however, is the most prevalent form of cancer caused by hexavalent chromium. Typically, industrial workers exposed to hexavalent chromium on a daily basis develop lung cancer. Since there is not a method to definitely diagnose cancer caused uniquely by hexavalent chromium exposure, there may be other more prevalent forms of cancer not yet attributed to hexavalent chromium.
References
http://www.livestrong.com/article/315080-side-effects-of-hexavalent-chromium/#ixzz1cmhq1oe3
Tertiary Treatment;
o Adsorption;
Activated carbon; Activated carbon is a carbon material mostly derived from charcoal. The unique structure of activated carbon produces a very large surface area: 1 lb of granular activated carbon typically provides a surface area of 125 acres (1 Kg =1,000,000 sq. m.). The activated carbon surface is non-polar which results in an affinity for non-polar adsorbates such as organics. Activated carbon is very effective in applications requiring air or water purification as well as precious metal recovery or removal.
· Its production;
· Its properties;
Activated
Carbon properties at a glance
|
||||
Property
|
Coconut
|
Coal
|
Lignite
|
Wood (Powder)
|
Micro-pores (diameter range less than 2nm)
|
High
|
High
|
Medium
|
Low
|
Macro-pores (diameter range above 25 nm)
|
Low
|
Medium
|
High
|
High
|
Hardness
|
High
|
High
|
Low
|
n/a
|
Ash
|
5%
|
10%
|
20%
|
5%
|
Water Soluble Ash
|
High
|
Low
|
High
|
Medium
|
Dust Reactivation
|
Good
|
Good
|
Poor
|
None
|
Apparent Density
|
0.48 g/cc
|
0.48 g/cc
|
0.4 g/cc
|
0.35 g/cc
|
Iodine No.
|
1100
|
1000
|
600
|
1000
|
Water Treatment (Liquid Phase)
|
Common Usage Scenarios
|
Liquid phase applications requiring
quick adsorption times
|
Liquid phase applications requiring
quick adsorption times
|
Liquid phase applications requiring
quick adsorption times
|
Liquid phase applications requiring
quick adsorption times
|
Wastewater treatment, groundwater
remediation, chemical purification, food grade applications, pharmaceutical,
and potable water treatment
|
Wastewater treatment, groundwater
remediation, chemical purification, food grade applications, pharmaceutical,
and potable water treatment
|
Applications where superior kinetic
properties are required including removal of low concentrations of normally
poorly adsorbed organics from groundwater and wastewaters
|
Applications where superior kinetic
properties are required including removal of low concentrations of normally
poorly adsorbed organics from groundwater and wastewaters
|
Applications where superior kinetic
properties are required including removal of low concentrations of normally
poorly adsorbed organics from groundwater and wastewaters
|
Applications where superior kinetic
properties are required including removal of low concentrations of normally
poorly adsorbed organics from groundwater and wastewaters
|
Ideal for many liquid phase
applications including the removal of organics from water streams, cleaner
then most other carbons
|
Ideal for many liquid phase
applications including the removal of organics from water streams, cleaner
then most other carbons
|
Wastewater treatment, groundwater
remediation, chemical purification, food grade applications, pharmaceutical,
and potable water treatment
|
Wastewater treatment, groundwater
remediation, chemical purification, food grade applications, pharmaceutical,
and potable water treatment
|
Ideal for many liquid phase
applications including the removal of organics from water streams, cleaner
then most other carbons
|
Ideal for many liquid phase
applications including the removal of organics from water streams, cleaner
then most other carbons
|
Correct pore size distribution is necessary to facilitate the adsorption process by providing adsorption sites and the appropriate channels to transport the adsorbate. Activated Carbon Pores can be divided into three general sizes:
Micro-pores (diameter in the range of less than 2nm)
Meso-pores (diameter in the range of 2 – 25 nm)
Macro-pores (diameter in the range of above 25 nm)
Ion exchange; water demineralization;
Ion exchange is a reversible chemical
reaction wherein ions (atoms or molecules that
have lost or gained an electron and thus acquired an electrical
charge) present in a solution are exchanged for a similarly charged ion
attached to an immobile solid particle of ion exchange material. By
charging (i.e., treating) ion exchange material with an acid,
usually sulfuric acid (H2SO4) or hydrochloric
acid (HCl), positively charged hydrogen ions
(H+) are attached to sites on the ion exchange material. Those H+ ions will attract and exchange places
with other positively charged ions (called cations)
present in a solution brought into contact with the positively charged H+ ions.
Similarly, by charging ion exchange
material with a caustic such as sodium
hydroxide (NaOH),
negatively charged hydroxide ions (OH-) are attached to
sites on the ion exchange material. Those sites will attract and exchange
places with other negatively charged ions (called anions) present in a solution
brought into contact with the negatively charged OH-
The adjacent diagram schematically
depicts an acid treated bead of ion exchange resin with its attached H+ ions (referred to as cation resin) and a caustic
treated bead of ion exchange resin with its attached OH- ions (referred to as an "anion
resin"). As shown in the diagram, when those beads are contacted with sodium cations
(Na+) and chlorine anions
(Cl-) derived from dissolved sodium
chloride (NaCl) in the
steam condensate:
· The Na+ cations are attracted to the cation
resin and exchange places with the H+ cations on the resin.
· The Cl- anions are attracted to the anion
resin and exchange place with the OH-
· The H+ cations removed from the cation resin
and the OH-
That illustrates how ion exchange
material removes dissolved substances from steam condensate or any other
solution. The process is sometimes referred to as demineralization (DM) or deionization
(DI).
Once all of the charged ions attached
on the cation and anion exchange materials have been replaced by ions removed
from a solution, the ion exchange materials are referred to as spent. The spent materials can
be regenerated (i.e., rejuvenated) by once again being charged with acid or
caustic.
The ion exchange materials can be naturally occurring zeolites or synthetically produced polymeric
resins. The synthetic resins are the most commonly used today
because their characteristics can be tailored to specific applications.- An anion exchange membrane has cation active agents, so it electrostatically lets anions move through.
- Inflowing water is distributed to EDI cells. When the direct current electricity is supplied, cations in the water go through the cation exchange membrane toward the negative electrode while anions pass through the anion exchange membrane toward the cation electrode.
- Demineralized water is produced in the diluting chamber with the ions eliminated while ion-enriched chamber produces or circulates enriched water.
What are Ion Exchange Resins?
Ion exchange resins can be made from synthetic or natural materials shaped into grain-of-sand-sized beads. Ions are negatively or positively charged atoms or molecules. The ion exchange resins have the opposite charge of the contaminant ions they are treating. This causes contaminants in water pumped through a container of ion exchange resin to be attracted to and stick to the resin similar to the way metal reacts to a magnet. When the contaminant ion attaches to the resin, it displaces another similarly charged ion into the water being treated. That ion is "exchanged" for the contaminant.
Pure oxidation;
Ozonation;
Oxidation
The main process steps are as follows :
Applications
This process has been studied extensively and found to work with up to a 60% reduction in excess sludge. Other benefits of the process that have been observed include: elimination of foaming problems, reduction in bulking, improvement in dewatering, improvements in settling and improvement in effluent quality. Ozone is already used at some sewage treatment plants for disinfection of treated effluent. In this application it has the benefits of improved disinfection, reductions in disinfection by-product and increasing the oxygen content of the water. Extension of ozone to the activated sludge process may further improve wastewater treatment plant economics and performance.Ozonation;
How is Ozone
Generated?
Corona Discharge: Air which is dry, or air which is dried
and passed through a device which concentrates oxygen from the air is run
through a high voltage arc (5,000 volts and up). The electrons in the
field split some of the oxygen and the individual oxygen atoms recombine with
normal oxygen to produce ozone. Concentrations are typically in the one
(1) to ten (10) percent range.
O2 + High Energy Electrons → O-
+O-O2 + O-→O3
Chemistry and mechanism;Oxidation
- Ozone reacts with bather loading and combined halogens;
- Reduces contaminants to inert compounds or carbon dioxide and water;
- Oxidizes combined halogens.
- Ozone removes metals (iron, manganese, zinc, copper, etc.)
- Oxidized organics also precipitate
- Filtration and clarification are enhanced by precipitation
- Ozone is the most powerful disinfectant available
- Rapidly kills bacteria and virusesUse in sludge disinfection
The main process steps are as follows :
- Sedimentation of suspended solids or filtration depending on the level of TSS (Total Suspended Solids)
- pH adjustment if necessary, usually determined after a feasibility test in the lab
- AOP Electro-catalytic reactor
- DAF or Lamella clarification. At this stage 30-60% of COD is reduced.
- AOP catalytic oxidation in either a tank or a underground pit (optional)
- Post filtration to remove any suspended catalyst particles.
- Disinfection
- Cyst Inactivation
- Viral and Bacterial Inactivation
- Control Biofouling
- Oxidation of Organic Compounds
- Iron and Manganese Removal
- Oxidation of Sulfides
- Chemical Reduction and/or Elimination
- Chemical Enhancement
- Oxidize VOC
- Promotion of Biodegradability
- Odor Control
- Water Recycling
Principles and technology;
Membrane technologies include reverse osmosis (RO), nanofiltration (NF), ultrafiltration (UF), microfiltration (MF), pervaporation (PV) and electrodialysis (ED). Two areas of special concern are membrane fouling (and cleaning) and energy consumption characteristics of various membranes and modules.
Membrane structure;
Two areas of special concern are membrane fouling (and cleaning) and energy consumption characteristics of various membranes and modules. Membrane separation processes have very important role in separation industry. reverse osmosis, electrolysis, dialysis, electrodialysis, gas separation, vapor permeation, pervaporation, membrane distillation, and membrane contactors. All processes except for pervaporation involve no phase change. All processes except electro-dialysis are pressure driven. Microfltration and ultrafiltration is widely used in food and beverage processing (beer microfiltration, apple juice ultrafiltration), biotechnological applications and pharmaceutical industry (antibiotic production, protein purification), water purification and wastewater treatment, microelectronics industry, and others. Nanofiltration and reverse osmosis membranes are mainly used for water purification purposes. Dense membranes are utilized for gas separations (removal of CO2 from natural gas, separating N2 from air, organic vapor removal from air or nitrogen stream) and sometimes in membrane distillation. The later process helps in separating of azeotropic compositions reducing the costs of distillation processes.
Nevertheless, they were not considered technically important until mid-1970. ,
microfiltration
Membrane separation processes differ based on separation mechanisms and size of the separated particles. The widely used membrane processes include
Membrane variation; its application
Membrane process
Membrane technologies include reverse osmosis (RO), nanofiltration (NF), ultrafiltration (UF), microfiltration (MF), pervaporation (PV) and electrodialysis (ED). Two areas of special concern are membrane fouling (and cleaning) and energy consumption characteristics of various membranes and modules.
Two areas of special concern are membrane fouling (and cleaning) and energy consumption characteristics of various membranes and modules.
Membrane separation processes have very important role in separation industry. Nevertheless, they were not considered technically important until mid-1970. Membrane separation processes differ based on separation mechanisms and size of the separated particles. The widely used membrane processes include microfiltration, reverse osmosis, electrolysis, dialysis, electrodialysis, gas separation, vapor permeation, pervaporation, membrane distillation, and membrane contactors. All processes except for pervaporation involve no phase change. All processes except electro-dialysis are pressure driven. Microfltration and ultrafiltration is widely used in food and beverage processing (beer microfiltration, apple juice ultrafiltration), biotechnological applications and pharmaceutical industry (antibiotic production, protein purification), water purification and wastewater treatment, microelectronics industry, and others. Nanofiltration and reverse osmosis membranes are mainly used for water purification purposes. Dense membranes are utilized for gas separations (removal of CO2 from natural gas, separating N2 from air, organic vapor removal from air or nitrogen stream) and sometimes in membrane distillation. The later process helps in separating of azeotropic compositions reducing the costs of distillation processes.
Membrane performance and governing equations
The selection of synthetic membranes for a targeted separation process is usually based on few requirements. Membranes have to provide enough mass transfer area to process large amounts of feed stream. The selected membrane has to have high selectivity (rejection) properties for certain particles; it has to resist fouling and to have high mechanical stability. It also needs to be reproducible and to have low manufacturing costs. The main modeling equation for the dead-end filtration at constant pressure drop is represented by Darcy’s law:
where Vp and Q are the volume of the permeate and its volumetric flow rate respectively
(proportional to same characteristics of the feed flow), μ is dynamic viscosity of permeating fluid, A is membrane area, Rm and R are the respective resistances of membrane and growing deposit of the foulants. Rm can be interpreted as a membrane resistance to the solvent (water) permeation. This resistance is a membrane intrinsic property and expected to be fairly constant and independent of the driving force, Δp. R is related to the type of membrane foulant, its concentration in the filtering solution, and the nature of foulant-membrane interactions. Darcy’s law allows to calculate the membrane area for a targeted separation at given conditions. The solute sieving coefficient is defined by the equation:
where Cf and Cp are the solute concentrations in feed and permeate respectively. Hydraulic permeability is defined as the inverse of resistance and is represented by the equation:
where J is the permeate flux which is the volumetric flow rate per unit of membrane area. The solute sieving coefficient and hydraulic permeability allow the quick assessment of the synthetic membrane performance.
References
Reverse Osmosis (RO) filtration;
Mitsubishi Rayon was the first company in the world to commercialize a multi-layered composite hollow-fibre membrane, a membrane with a completely new structure, and one which has superior permeability to gases. This membrane features an ultra-thin non-porous membrane sandwiched between two porous membranes. Thanks to its non-multi-porous structure, the membrane prevents permeation of most liquid at the non-pressurized side. As the non-porous membrane is ultra-thin, it has superior performance in letting through gases. As the non-porous membrane is sandwiched between two polyethylene porous membranes, it displays excellent damage resistance. It is possible to remove dissolved oxygen in water to below 1µg/L.
Tubular
· Tubular membrane filters have a wide center channel - which better handles feed streams with large solids and high levels of suspended soils without clogging
· Excellent, cost-effective replacement tubular membranes fit nearly any existing in-plant systems
· Direct replacement of KochT Tubular Membranes
· Automatic Sponge ball cleaning system promotes easy maintenance, less downtime
· High cross flow velocities prevent membrane fouling, especially in applications with difficult process and waste streams
Spiral-wound
The core of each spiral element is a perforated central tube, with large membrane pockets attached. Each of these contains a spacer net that transports the permeate out of the membrane pocket and into the central tube. Different thicknesses of spacer net between each pocket make sure the feed is evenly distributed over the entire surface of the membrane. The exceptional characteristics is that its elements ensure fewer channelling problem whenever there’s a high pressure drop across these membrane as its special material that would withstand high temperatures and extreme pH values.Use in Electrodialysis;
Electrodialysis (ED) system is a membrane separation process driven by voltage. Salt is moved through the membrane using electrical potential thereby leaving fresh water behind as product water. After its introduction in 1960s it is used for various industrial applications. However the major area of activity of this system is seawater and brackish water desalination.
Principles of Electrodialysis Process
Electrodialysis process depends on the following general principles:
Dissolved salts in the water are mostly ionic that is they are either positively charged or negatively charged.
These ions are attracted towards the opposite charged electrodes.
The charged particles can be either allowed or prohibited to pass through membrane built for the purpose.
How Electrodialysis System Functions?
The saline solution consist of dissolved salts like Na+, Ca2+, and CO32- .
These ionic salts move towards the electrode with the opposite charge when the electric current is passed through these electrodes. In these phenomena either the negatively charged particles or the positively charged particles will pass the membranes which are placed between a pair of electrodes. Membranes that are anion-selective membrane and cation-selective membrane, are arranged in an alternative fashion. Between each pair of membrane there is a spacer sheet that allows the water to flow along the face of the membrane.
The spacers separate the product water and the brine. Due to the action of electrodes, spacers and membranes the concentrated and the diluted solution is created in the spaces between the alternating membranes.
The spaces between the two membranes are called cells. The pair of cells consists of two cells. From one cell ions migrated. This is the dilute cell of the product water whereas in the other cell the ions concentrate. This concentrate cell is meant for the brine stream.
One electrodialysis unit comprises of numerous pair of cells that are bound together with electrodes on the outside. The bounded cell is referred as a membrane stack. Feed water passes through all of the cells in order to provide a continuous flow of desalted water and brine to emerge from the stack. Anti-scaling chemicals can be added to the streams in the stack to protect it from common salt-based scaling.
Pre-Treatment and Post Treatment
Before actual operation feed water is firstly pre-treated in order to prevent materials from harming the membranes or clog the narrow channels in the cells from entering the membrane stack. Low pressure pump is used to push the feed water through the stack. The feed water is forced with enough power to overcome the resistance of the water as it passes through the narrow passages. In the post treatment water is stabilized and prepared for distribution. In this treatment water the pH is adjusted and gases like hydrogen sulfide is removed.
WWTP Troubleshooting
· Chemical coagulation
o Theory of coagulation & flocculation;
o Coagulation failure;
o Flocculation failure
· Biological flocculation
o Bulking issues
§ ‘ashing’ and ‘gassing’
§ The filamentous organisms
o Chemical remediation – odour issues
· Sludge drying failure
· Equipments: pump, mixer, blower, metal tanks, valves and pH meter
WWTP Maintenance
· EQ tanks; pumps; coagulation tanks; clarifier tanks; scrapers; sludge pumps; mixer blowers; filter press; chemical dosing system; anti or de-scaling chemicals.
Sludge Management
Ø Definition;
Ø Overview of sludge management methods;
Ø Disposal;
Ø Characteristics;
o Physical;
o Biological;
o Biochemical;
Ø Processing;
o Objectives;
o Options;
Ø Treatment;
o Stabilization;
§ Lime, chlorine, oxygen, heat, UV, radiation, drying & combustion;
§ Incinerator;
§ Pyrolysis;
§ Wet oxidation;
§ composting
Disposal summary;
Two areas of special concern are membrane fouling (and cleaning) and energy consumption characteristics of various membranes and modules. Membrane separation processes have very important role in separation industry. reverse osmosis, electrolysis, dialysis, electrodialysis, gas separation, vapor permeation, pervaporation, membrane distillation, and membrane contactors. All processes except for pervaporation involve no phase change. All processes except electro-dialysis are pressure driven. Microfltration and ultrafiltration is widely used in food and beverage processing (beer microfiltration, apple juice ultrafiltration), biotechnological applications and pharmaceutical industry (antibiotic production, protein purification), water purification and wastewater treatment, microelectronics industry, and others. Nanofiltration and reverse osmosis membranes are mainly used for water purification purposes. Dense membranes are utilized for gas separations (removal of CO2 from natural gas, separating N2 from air, organic vapor removal from air or nitrogen stream) and sometimes in membrane distillation. The later process helps in separating of azeotropic compositions reducing the costs of distillation processes.
Membrane variation; its application
Membrane technologies include reverse osmosis (RO), nanofiltration (NF), ultrafiltration (UF), microfiltration (MF), pervaporation (PV) and electrodialysis (ED). Two areas of special concern are membrane fouling (and cleaning) and energy consumption characteristics of various membranes and modules.
Membrane separation processes have very important role in separation industry. Nevertheless, they were not considered technically important until mid-1970. Membrane separation processes differ based on separation mechanisms and size of the separated particles. The widely used membrane processes include microfiltration, reverse osmosis, electrolysis, dialysis, electrodialysis, gas separation, vapor permeation, pervaporation, membrane distillation, and membrane contactors. All processes except for pervaporation involve no phase change. All processes except electro-dialysis are pressure driven. Microfltration and ultrafiltration is widely used in food and beverage processing (beer microfiltration, apple juice ultrafiltration), biotechnological applications and pharmaceutical industry (antibiotic production, protein purification), water purification and wastewater treatment, microelectronics industry, and others. Nanofiltration and reverse osmosis membranes are mainly used for water purification purposes. Dense membranes are utilized for gas separations (removal of CO2 from natural gas, separating N2 from air, organic vapor removal from air or nitrogen stream) and sometimes in membrane distillation. The later process helps in separating of azeotropic compositions reducing the costs of distillation processes.
The selection of synthetic membranes for a targeted separation process is usually based on few requirements. Membranes have to provide enough mass transfer area to process large amounts of feed stream. The selected membrane has to have high selectivity (rejection) properties for certain particles; it has to resist fouling and to have high mechanical stability. It also needs to be reproducible and to have low manufacturing costs. The main modeling equation for the dead-end filtration at constant pressure drop is represented by Darcy’s law:
(proportional to same characteristics of the feed flow), μ is dynamic viscosity of permeating fluid, A is membrane area, Rm and R are the respective resistances of membrane and growing deposit of the foulants. Rm can be interpreted as a membrane resistance to the solvent (water) permeation. This resistance is a membrane intrinsic property and expected to be fairly constant and independent of the driving force, Δp. R is related to the type of membrane foulant, its concentration in the filtering solution, and the nature of foulant-membrane interactions. Darcy’s law allows to calculate the membrane area for a targeted separation at given conditions. The solute sieving coefficient is defined by the equation:
References
§
Osada, Y., Nakagawa, T., Membrane Science and Technology,
New York
§
Zeman, Leos J., Zydney, Andrew
L., Microfiltration and
Ultrafitration, Principles and Applications., New York
§
Mulder M., Basic Principles of Membrane
Technology, Kluwer Academic Publishers, Netherlands
§
Jornitz, Maik W., Sterile Filtration, Springer, Germany
§
Van Reis R., Zydney A. Bioprocess
membrane technology. J Mem Sci.
297(2007): 16-50.
§
Templin T., Johnston D., Singh
V., Tumbleson M.E.
§
Ripperger S., Schulz G.
Microporous membranes in biotechnical applications. Bioprocess Eng.
§
Thomas Melin, Robert Rautenbach, Membranverfahren, Springer, Germany
§
Munir Cheryan, Handbuch Ultrafiltration, Behr,
1990, ISBN 3-925673-87-3.
Membrane geometrics
Hollow-FibreMitsubishi Rayon was the first company in the world to commercialize a multi-layered composite hollow-fibre membrane, a membrane with a completely new structure, and one which has superior permeability to gases. This membrane features an ultra-thin non-porous membrane sandwiched between two porous membranes. Thanks to its non-multi-porous structure, the membrane prevents permeation of most liquid at the non-pressurized side. As the non-porous membrane is ultra-thin, it has superior performance in letting through gases. As the non-porous membrane is sandwiched between two polyethylene porous membranes, it displays excellent damage resistance. It is possible to remove dissolved oxygen in water to below 1µg/L.
Tubular
· Tubular membrane filters have a wide center channel - which better handles feed streams with large solids and high levels of suspended soils without clogging
· Excellent, cost-effective replacement tubular membranes fit nearly any existing in-plant systems
· Direct replacement of KochT Tubular Membranes
· Automatic Sponge ball cleaning system promotes easy maintenance, less downtime
· High cross flow velocities prevent membrane fouling, especially in applications with difficult process and waste streams
Spiral-wound
Electrodialysis (ED) system is a membrane separation process driven by voltage. Salt is moved through the membrane using electrical potential thereby leaving fresh water behind as product water. After its introduction in 1960s it is used for various industrial applications. However the major area of activity of this system is seawater and brackish water desalination.
Electrodialysis process depends on the following general principles:
Dissolved salts in the water are mostly ionic that is they are either positively charged or negatively charged.
These ions are attracted towards the opposite charged electrodes.
The charged particles can be either allowed or prohibited to pass through membrane built for the purpose.
How Electrodialysis System Functions?
The saline solution consist of dissolved salts like Na+, Ca2+, and CO32- .
These ionic salts move towards the electrode with the opposite charge when the electric current is passed through these electrodes. In these phenomena either the negatively charged particles or the positively charged particles will pass the membranes which are placed between a pair of electrodes. Membranes that are anion-selective membrane and cation-selective membrane, are arranged in an alternative fashion. Between each pair of membrane there is a spacer sheet that allows the water to flow along the face of the membrane.
The spacers separate the product water and the brine. Due to the action of electrodes, spacers and membranes the concentrated and the diluted solution is created in the spaces between the alternating membranes.
The spaces between the two membranes are called cells. The pair of cells consists of two cells. From one cell ions migrated. This is the dilute cell of the product water whereas in the other cell the ions concentrate. This concentrate cell is meant for the brine stream.
One electrodialysis unit comprises of numerous pair of cells that are bound together with electrodes on the outside. The bounded cell is referred as a membrane stack. Feed water passes through all of the cells in order to provide a continuous flow of desalted water and brine to emerge from the stack. Anti-scaling chemicals can be added to the streams in the stack to protect it from common salt-based scaling.
Pre-Treatment and Post Treatment
Before actual operation feed water is firstly pre-treated in order to prevent materials from harming the membranes or clog the narrow channels in the cells from entering the membrane stack. Low pressure pump is used to push the feed water through the stack. The feed water is forced with enough power to overcome the resistance of the water as it passes through the narrow passages. In the post treatment water is stabilized and prepared for distribution. In this treatment water the pH is adjusted and gases like hydrogen sulfide is removed.
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| Overall IETS/WWTP – Integrated overview of all units – summary |
WWTP Troubleshooting
· Chemical coagulation
o Theory of coagulation & flocculation;
o Coagulation failure;
o Flocculation failure
· Biological flocculation
o Bulking issues
§ ‘ashing’ and ‘gassing’
§ The filamentous organisms
o Chemical remediation – odour issues
· Sludge drying failure
· Equipments: pump, mixer, blower, metal tanks, valves and pH meter
WWTP Maintenance
· EQ tanks; pumps; coagulation tanks; clarifier tanks; scrapers; sludge pumps; mixer blowers; filter press; chemical dosing system; anti or de-scaling chemicals.
Sludge Management
Ø Definition;
Ø Overview of sludge management methods;
Ø Disposal;
Ø Characteristics;
o Physical;
o Biological;
o Biochemical;
Ø Processing;
o Objectives;
o Options;
Ø Treatment;
o Stabilization;
§ Lime, chlorine, oxygen, heat, UV, radiation, drying & combustion;
§ Incinerator;
§ Pyrolysis;
§ Wet oxidation;
§ composting
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