Wastewater treatment for environment.pptx

water treatment for environmental engineering

1. Sewage/wastewater treatment 1 Notes by: Priyanka Kotoky, B.E. in C.E. , M.E. in C.E. ( W.R.E. ), Ph.D. in C.E. (Ongoing)

2. Types/sources of sewage/wastewater Municipal wastewater Mostly the spent water community activity draining into the sewer system with a fraction of storm water from the area draining into it. Wastewater from kitchen, bathroom, lavatory and laundries. Industrial wastewater Varies in composition with industrial operation. Normally contains rinse water, water heavily laden with organic and mineral matter or corrosive, poisons, flammable, or explosive substances. 2 Notes by: Priyanka Kotoky, B.E. in C.E. , M.E. in C.E. ( W.R.E. ), Ph.D. in C.E. (Ongoing)

3. Sewage/wastewater characteristics Temperature Colour Odour Solids (TS, TSS, TDS) pH Carbonaceous constituents (COD, BOD, TOC) Nitrogen (organic nitrogen, ammonia nitrogen, nitrite nitrogen, nitrate nitrogen) Phosphorus (organic phosphorus, orthophosphorus ) Chlorides Toxic metals and compounds Pathogen 3 Notes by: Priyanka Kotoky, B.E. in C.E. , M.E. in C.E. ( W.R.E. ), Ph.D. in C.E. (Ongoing)

4. Terminology in sewage/wastewater treatment Unit operations: Contaminant removal by physical force. Useful for removal of suspended solids b) Unit processes: Biological and/or chemical reactions. Useful for removal of biodegradable organics and pathogens c) Reactors: It refers to the vessel or contaminant structure along with its all appurtenances in which the unit operation/process takes place. d) Wastewater treatment system: It composed of combination of unit operations/process to reduce certain constituents of wastewater to an acceptable level. 4 Notes by: Priyanka Kotoky, B.E. in C.E. , M.E. in C.E. ( W.R.E. ), Ph.D. in C.E. (Ongoing)

5. 5 Notes by: Priyanka Kotoky, B.E. in C.E. , M.E. in C.E. ( W.R.E. ), Ph.D. in C.E. (Ongoing)

6. Reactors 1) Batch reactors: Flow neither enters nor leaves the reactor on continuous basis. 2) CST reactors: The contents are completely mixed and no concentration gradient exist. Flow enters and leaves on continuously basis. The concentration of a substance is same in the effluent and the reactor. 3) Plug flow reactor: Characterized by lack of mixing in the direction of flow means concentration gradient exist in the direction of flow. It is assumed that reactors are well mixed in transverse/lateral/radial direction. 4) Plug flow with dispersion reactor: Reactor has intermediate mixing, in between plug flow and CSTR. 6 Notes by: Priyanka Kotoky, B.E. in C.E. , M.E. in C.E. ( W.R.E. ), Ph.D. in C.E. (Ongoing)

7. Reactors Batch CSTR Plug flow Plug flow with dispersion 7 Notes by: Priyanka Kotoky, B.E. in C.E. , M.E. in C.E. ( W.R.E. ), Ph.D. in C.E. (Ongoing)

8. Sewage/w astewater treatment processes Pre-treatment Preliminary treatment Primary treatment Secondary treatment Tertiary treatment Sludge ( biosolids ) disposal 8 Notes by: Priyanka Kotoky, B.E. in C.E. , M.E. in C.E. ( W.R.E. ), Ph.D. in C.E. (Ongoing)

9. Pre-treatment Occurs in business or industry prior to discharge. Prevention of toxic chemicals or excess nutrients being discharged in wastewater. Preliminary treatment Removes large objects and non-degradable materials. Protects pumps and equipment from damage. Bar screen and grit chamber. 9 Notes by: Priyanka Kotoky, B.E. in C.E. , M.E. in C.E. ( W.R.E. ), Ph.D. in C.E. (Ongoing)

10. 10 Notes by: Priyanka Kotoky, B.E. in C.E., M.E. in C.E. (W.R.E.), Ph.D. in C.E. (Ongoing)

11. Bar screen Used to remove large objects, such as rags and plastics, bottles, pieces of wood, etc. from wastewater. Part of the primary filtration flow and typically is the first, or preliminary, level of filtration, being installed at the influent to a wastewater treatment plant. Typically consist of a series of vertical steel bars spaced between 1 and 3 inches apart. 11 Notes by: Priyanka Kotoky, B.E. in C.E. , M.E. in C.E. ( W.R.E. ), Ph.D. in C.E. (Ongoing)

12. Grit chamber remove the inorganic particles to prevent damage to the pumps, and to prevent their accumulation in sludge digestors . like sedimentation tanks, designed to separate the intended heavier inorganic materials (specific gravity about 2.65) and to pass forward the lighter organic materials. flow velocity should neither be too low as to cause the settling of lighter organic matter, nor should it be too high as not to cause the settlement of the silt and grit present in the sewage. 12 Notes by: Priyanka Kotoky, B.E. in C.E., M.E. in C.E. (W.R.E.), Ph.D. in C.E. (Ongoing)

13. For proper functioning, the velocity should not be allowed to change in spite of change in flow in the grit chamber. This can be achieved by provision of Proportional weir or Parshall flume. 13 Notes by: Priyanka Kotoky, B.E. in C.E., M.E. in C.E. (W.R.E.), Ph.D. in C.E. (Ongoing)

14. Disposal of grit In large treatment plant, grit is incinerated with sludge. In the past, grits along with screening was dumped into sea. Generally, grit should be washed before disposal to remove organic matter. Land disposal after washing is most common. 14 Notes by: Priyanka Kotoky, B.E. in C.E. , M.E. in C.E. ( W.R.E. ), Ph.D. in C.E. (Ongoing)

15. Objectives To reduce the strength of sewage to the extent 30% to 50%. To remove settleable solids by 80% to 90%. To reduce BOD by 30% to 35%. To make the sewage fit for further treatment process. Primary treatment 15 Notes by: Priyanka Kotoky, B.E. in C.E. , M.E. in C.E. ( W.R.E. ), Ph.D. in C.E. (Ongoing)

16. Primary sedimentation tank Located just after grit chamber. It may be rectangular, circular or square shape. The principle and construction details are same as that of plain sedimentation tank W.T.P. 16 Notes by: Priyanka Kotoky, B.E. in C.E. , M.E. in C.E. ( W.R.E. ), Ph.D. in C.E. (Ongoing)

17. Circular sedimentation tank 17 Notes by: Priyanka Kotoky, B.E. in C.E. , M.E. in C.E. ( W.R.E. ), Ph.D. in C.E. (Ongoing)

18. Purposes: oxidizing carbonaceous biological matter. oxidizing nitrogenous matter: mainly ammonium and nitrogen in biological matter. removing nutrients (nitrogen and phosphorus ). Secondary treatment 18 Notes by: Priyanka Kotoky, B.E. in C.E. , M.E. in C.E. ( W.R.E. ), Ph.D. in C.E. (Ongoing)

19. Activated sludge process The most common suspended growth process used for municipal wastewater treatment. Activated sludge plant involves: wastewater aeration in the presence of a microbial suspension. solid-liquid separation following aeration. discharge of clarified effluent. wasting of excess biomass. return of remaining biomass to the aeration tank. 19 Notes by: Priyanka Kotoky, B.E. in C.E. , M.E. in C.E. ( W.R.E. ), Ph.D. in C.E. (Ongoing)

20. 20 Notes by: Priyanka Kotoky, B.E. in C.E. , M.E. in C.E. ( W.R.E. ), Ph.D. in C.E. (Ongoing)

21. Aeration methods Diffused aeration Sewage liquor is run into deep tanks with diffuser blocks attached to the floor. These are like the diffuser blocks used in tropical fish tanks but on a much larger scale. Air is pumped through the blocks and the curtain of bubbles formed both oxygenates the liquor and also provide the necessary stirring action. Where capacity is limited or the sewage is unusually strong or difficult to treat, oxygen may be used instead of air. Typically, the air is generated by some type of blower or compressor. 21 Notes by: Priyanka Kotoky, B.E. in C.E. , M.E. in C.E. ( W.R.E. ), Ph.D. in C.E. (Ongoing)

22. Surface aerators Vertically mounted tubes of up to 1 m diameter extending from just above the base of a deep concrete tank to just below the surface of the sewage liquor. A typical shaft might be 10 m high. At the surface end the tube is formed into a cone with helical vanes attached to the inner surface. When the tube is rotated, the vanes spin liquor up and out of the cones drawing new sewage liquor from the base of the tank. In many works each cone is located in a separate cell that can be isolated from the remaining cells if required for maintenance. Some works may have two cones to a cell and some large works may have 4 cones per cell. 22 Notes by: Priyanka Kotoky, B.E. in C.E. , M.E. in C.E. ( W.R.E. ), Ph.D. in C.E. (Ongoing)

23. Trickling filters Attached growth process  i.e. process in which microorganisms responsible for treatment are attached to an inert packing material. Packing material include rock, gravel, slag, sand, redwood, and a wide range of plastic and other synthetic materials. Filter media - very high surface area to volume. Materials - porous and have considerable internal surface area in addition to the external surface of the medium. Removal of pollutants involves both  absorption and adsorption  of organic compounds. 23 Notes by: Priyanka Kotoky, B.E. in C.E. , M.E. in C.E. ( W.R.E. ), Ph.D. in C.E. (Ongoing)

24. Biofilm Formation of a biofilm begins with the attachment of free-floating microorganisms to a surface. Bio-film that develops in a trickling filter may become several millimetres thick and is typically a gelatinous matrix that contains many species of bacteria, cilliates and amoeboid protozoa, annelids, round worms and insect larvae and many other micro fauna. Within the thickness of the biofilm both aerobic and anaerobic zones can exist supporting both oxidative and reductive biological processes. 24 Notes by: Priyanka Kotoky, B.E. in C.E. , M.E. in C.E. ( W.R.E. ), Ph.D. in C.E. (Ongoing)

25. 25 Notes by: Priyanka Kotoky, B.E. in C.E. , M.E. in C.E. ( W.R.E. ), Ph.D. in C.E. (Ongoing)

26. Rotating biological contactor Fixed-bed reactors consisting of stacks of rotating disks mounted on a horizontal shaft. They are partially submerged and rotated as wastewater flows through. They are used in conventional wastewater treatment plants as secondary treatment after primary sedimentation of domestic grey- or blackwater , or any other biodegradable effluent. The microbial community is alternately exposed to the atmosphere and the wastewater, allowing both aeration and assimilation of dissolved organic pollutants and nutrients for their degradation. 26 Notes by: Priyanka Kotoky, B.E. in C.E. , M.E. in C.E. ( W.R.E. ), Ph.D. in C.E. (Ongoing)

27. Advantages High contact time and high effluent quality (both BOD and nutrients ). High process stability, resistant to shock hydraulic or organic loading. Short contact periods are required because of the large active surface. Low space requirement. Well drainable excess sludge collected in clarifier. Low sludge production. Disadvantages Continuous electricity supply required (but uses less energy than trickling filters or activated sludge processes for comparable degradation rates ). High investment as well as operation and maintenance costs. Must be protected against sunlight, wind and rain. Odour problems may occur. Requires permanent skilled technical labour for operation and maintenance. 27 Notes by: Priyanka Kotoky, B.E. in C.E. , M.E. in C.E. ( W.R.E. ), Ph.D. in C.E. (Ongoing)

28. Upflow anaerobic sludge blanket   Normally referred to as UASB reactor. UASB uses an anaerobic process whilst forming a blanket of granular sludge which suspends in the tank. Wastewater flows upwards through the blanket and is processed (degraded) by the anaerobic microorganisms. Upward flow combined with the settling action of gravity suspends the blanket with the aid of flocculants. Biogas with a high concentration of methane is produced as a by-product. 28 Notes by: Priyanka Kotoky, B.E. in C.E. , M.E. in C.E. ( W.R.E. ), Ph.D. in C.E. (Ongoing)

29. 29 Notes by: Priyanka Kotoky, B.E. in C.E., M.E. in C.E. (W.R.E.), Ph.D. in C.E. (Ongoing)

30. A typical arrangement of a UASB type treatment plant for municipal sewage would be as follows: Initial pumping Screening and degritting Main UASB reactor Gas collection and conversion or conveyance Sludge drying bed Post treatment facility 30 Notes by: Priyanka Kotoky, B.E. in C.E. , M.E. in C.E. ( W.R.E. ), Ph.D. in C.E. (Ongoing)

31. Constructed wetlands Where adequate land is available , stabilization ponds with constructed wetland ecosystems can be built to perform secondary treatment separated from the natural wetlands receiving secondary treated sewage. Constructed wetlands resemble fixed-film systems more than suspended growth systems, because natural mixing is minimal. Constructed wetland design uses plug flow assumptions to compute the residence time required for treatment. Patterns of vegetation growth and solids deposition in wetland ecosystems, however, can create preferential flow pathways which may reduce average residence time . Measurement of wetland treatment efficiency is complicated because most traditional water quality measurements cannot differentiate between sewage pollutants and biological productivity of the wetland. 31 Notes by: Priyanka Kotoky, B.E. in C.E. , M.E. in C.E. ( W.R.E. ), Ph.D. in C.E. (Ongoing)

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35. 35 Notes by: Priyanka Kotoky, B.E. in C.E. , M.E. in C.E. ( W.R.E. ), Ph.D. in C.E. (Ongoing)

36. Tertiary treatment The purpose of tertiary treatment (also called "advanced treatment") is to provide a final treatment stage to further improve the effluent quality before it is discharged to the receiving environment (sea, river, lake, wet lands, ground, etc.). Tertiary treatment may include biological nutrient removal (alternatively, this can be classified as secondary treatment), disinfection and removal of micro pollutants , such as  environmental persistent pharmaceutical pollutants . 36 Notes by: Priyanka Kotoky, B.E. in C.E. , M.E. in C.E. ( W.R.E. ), Ph.D. in C.E. (Ongoing)

37. Sludge management 37 Notes by: Priyanka Kotoky, B.E. in C.E. , M.E. in C.E. ( W.R.E. ), Ph.D. in C.E. (Ongoing)

38. Sewage sludge The residue that accumulates in sewage treatment plants is called sludge (or biosolids ). Sewage sludge is the solid, semisolid, or slurry residual material that is produced as a by-product of wastewater treatment processes. 38 Notes by: Priyanka Kotoky, B.E. in C.E. , M.E. in C.E. ( W.R.E. ), Ph.D. in C.E. (Ongoing)

39. This residue is commonly classified as primary and secondary sludge. Primary sludge is generated from chemical precipitation, sedimentation, and other primary processes. Secondary sludge is the activated waste biomass resulting from biological treatments. Some sewage plants also receive septage or septic tank solids from household on-site wastewater treatment systems. 39 Notes by: Priyanka Kotoky, B.E. in C.E. , M.E. in C.E. ( W.R.E. ), Ph.D. in C.E. (Ongoing)

40. Treatment methods Treatment of sewage sludge may include a combination of  thickening , digestion , and dewatering processes. Two basic goals of treating sludge before final disposal are to reduce its volume and to stabilize the organic materials. Stabilized sludge does not have an offensive odour and can be handled without causing a nuisance or health hazard. Smaller sludge volume reduces the costs of pumping and storage. 40 Notes by: Priyanka Kotoky, B.E. in C.E. , M.E. in C.E. ( W.R.E. ), Ph.D. in C.E. (Ongoing)

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42. 42 Notes by: Priyanka Kotoky, B.E. in C.E., M.E. in C.E. (W.R.E.), Ph.D. in C.E. (Ongoing)

43. Thickening Thickening is usually the first step in sludge treatment because it is impractical to handle thin sludge, a slurry of solids suspended in water. Thickening is usually accomplished in a tank called a gravity thickener. A thickener can reduce the total volume of sludge to less than half the original volume. An alternative to gravity thickening is dissolved-air flotation. In this method, air bubbles carry the solids to the surface, where a layer of thickened sludge forms. 43 Notes by: Priyanka Kotoky, B.E. in C.E. , M.E. in C.E. ( W.R.E. ), Ph.D. in C.E. (Ongoing)

44. Digestion Sludge digestion is a biological process in which organic solids are decomposed into stable substances. Digestion reduces the total mass of solids, destroys pathogens , and makes it easier to dewater or dry the sludge. Digested sludge is inoffensive, having the appearance and characteristics of a rich potting soil. Most large sewage treatment plants use a two-stage digestion system in which organics are metabolized by bacteria anaerobically (in the absence of oxygen ). 44 Notes by: Priyanka Kotoky, B.E. in C.E. , M.E. in C.E. ( W.R.E. ), Ph.D. in C.E. (Ongoing)

45. In the first stage, the sludge, thickened to a dry solids (DS) content of about 5 percent, is heated and mixed in a closed tank for several days. Acid-forming bacteria hydrolyze large molecules such as proteins and lipids, breaking them into smaller water-soluble molecules, and then ferment those smaller molecules into various fatty acids. The sludge then flows into a second tank, where the dissolved matter is converted by other bacteria into biogas, a mixture of carbon dioxide and methane. Methane is combustible and is used as a fuel to heat the first digestion tank as well as to generate electricity for the plant. 45 Notes by: Priyanka Kotoky, B.E. in C.E. , M.E. in C.E. ( W.R.E. ), Ph.D. in C.E. (Ongoing)

46. Anaerobic digestion is very sensitive to temperature, acidity, and other factors. It requires careful monitoring and control. In some cases, the sludge is inoculated with extra hydrolytic enzymes at the beginning of the first digestion stage in order to supplement the action of the bacteria. It has been found that this enzymatic treatment can destroy more unwanted pathogens in the sludge and also can result in the generation of more biogas in the second stage of digestion. 46 Notes by: Priyanka Kotoky, B.E. in C.E. , M.E. in C.E. ( W.R.E. ), Ph.D. in C.E. (Ongoing)

47. Thermal hydrolysis Another enhancement of the traditional two-stage anaerobic digestion process is thermal hydrolysis, or the breaking down of the large molecules by heat. This is done in a separate step before digestion. In a typical case, the process begins with a sludge that has been dewatered to a DS content of some 15 percent. 47 Notes by: Priyanka Kotoky, B.E. in C.E. , M.E. in C.E. ( W.R.E. ), Ph.D. in C.E. (Ongoing)

48. The sludge is mixed with steam in a pulper , and this hot homogenized mixture is fed to a reactor, where it is held under pressure at approximately 165 °C (about 330 °F) for about 30 minutes. At that point, with the hydrolytic reactions complete, some of the steam is bled off (to be fed to the pulper ), and the sludge, still under some pressure, is released suddenly into a “flash tank,” where the sudded drop in pressure bursts the cell walls of much of the solid matter. The hydrolyzed sludge is cooled, diluted slightly with water, and then sent directly to the second stage of anaerobic digestion. 48 Notes by: Priyanka Kotoky, B.E. in C.E. , M.E. in C.E. ( W.R.E. ), Ph.D. in C.E. (Ongoing)

49. Aerobic digestion Sludge digestion may also take place aerobically; that is, in the presence of oxygen. The sludge is vigorously aerated in an open tank for about 20 days. Methane gas is not formed in this process. Although aerobic systems are easier to operate than anaerobic systems, they usually cost more to operate because of the power needed for aeration. Aerobic digestion is often combined with small extended aeration or contact stabilization systems. 49 Notes by: Priyanka Kotoky, B.E. in C.E. , M.E. in C.E. ( W.R.E. ), Ph.D. in C.E. (Ongoing)

50. Dewatering Digested sewage sludge is usually dewatered before disposal. Dewatered sludge still contains a significant amount of water—often as much as 70 percent—but, even with that moisture content, sludge no longer behaves as a liquid and can be handled as a solid material. Sludge-drying beds provide the simplest method of dewatering. A digested sludge slurry is spread on an open bed of sand and allowed to remain until dry. 50 Notes by: Priyanka Kotoky, B.E. in C.E. , M.E. in C.E. ( W.R.E. ), Ph.D. in C.E. (Ongoing)

51. Disposal The final destination of treated sewage sludge usually is the land. Dewatered sludge can be buried underground in a sanitary landfill . It also may be spread on agricultural land in order to make use of its value as a soil conditioner and fertilizer. Since sludge may contain toxic industrial chemicals , it is not spread on land where crops are grown for human consumption. 51 Notes by: Priyanka Kotoky, B.E. in C.E. , M.E. in C.E. ( W.R.E. ), Ph.D. in C.E. (Ongoing)

52. Where a suitable site for land disposal is not available , as in urban areas, sludge may be incinerated . Incineration completely evaporates the moisture and converts the organic solids into inert ash. The ash must be disposed of, but the reduced volume makes disposal more economical. Air pollution control is a very important consideration when sewage sludge is incinerated. Appropriate air-cleaning devices such as scrubbers and filters must be used. Dumping sludge in the ocean , once an economical disposal method for many coastal communities, is no longer considered a viable option. It is now prohibited in the United States and many other coastal countries. 52 Notes by: Priyanka Kotoky, B.E. in C.E. , M.E. in C.E. ( W.R.E. ), Ph.D. in C.E. (Ongoing)

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