sewage waste water treatment

waste water treatment

1. Babasaheb bhimrao ambedkar university Submitted to- Dr. Suman Upadhyay Submitted by- Suchita Verma M.Sc 3 rd semester roll no- 110082

2. Introduction What is waste water? Wastewater is used water from any combination of domestic, industrial, commercial or agricultural activities, surface runoff and any sewer inflow or sewer infiltration . Types of wastewater include : a) domestic wastewater from households. b) municipal wastewater from communities (also called sewage).  c) industrial wastewater from industrial activities.

3. Wastewater can contain physical, chemical and biological pollutants . a) Chemical and physical pollutant Heavy metals including mercury, lead, and chromium Organic particles such as feces, hairs,  food, paper fibers, plant material, etc.; Soluble organic material such as urea, fruit sugar, soluble proteins, drugs, etc. Inorganic particles such as sand, grit, metal particles, ceramics, etc.; Soluble inorganic material such as ammonia, road-salt, sea-salt, cyanide, hydrogen sulfide, et Macro-solid such as household items. Emulsions such as paints, adhesives, mayonnaise, hair colorants, emulsified oils. Toxins such as pesticides, poisons, herbicides, etc.

4. b) Biological pollutants Bacteria (for example  Salmonella ,  Shigella ,  Campylobacter ,  Vibrio cholerae ) Viruses (for example  hepatitis A, rotavirus, enteroviruses ), Protozoa (for example  Entamoeba histolytica ,  Giardia ) Parasites such as helminths and their eggs (e.g.  Ascaris  (roundworm),  Ancylostoma  (hookworm),  Trichuris  (whipworm )); It can also contain non-pathogenic bacteria and animals such as  insects, arthropods, small fish .

5. Why to Treat Wastewater? It's a matter of caring for our environment and for our own health. There are a lot of good reasons why keeping our water clean is an important priority: a) Fisheries Clean water is critical to plants and animals that live in water. This is important to the fishing industry and future generations. b)Wildlife Habitats Our rivers and ocean waters teem with life that depends on shoreline, beaches and marshes. They are critical habitats for hundreds of species of fish and other aquatic life. Migratory water birds use the areas for resting and feeding. c)Health Concerns If it is not properly cleaned, water can carry disease. Since we live, work and play so close to water, harmful bacteria have to be removed to make water safe.

6. Objective of Waste Water Treatment: The objective of municipal and industrial waste water treatment:- a)extract pollutants b)remove toxicants c)Neutralize coarse particles d)kill pathogens so that quality of discharged water is improved to reach the permissible level of water to be discharged into water bodies or for agricultural land . Treatment of water thus aims at reduction of BOD, COD, eutrophication etc. of receiving water bodies and prevention of bio-magnification of toxic substances in food chain .

7. WASTE WATER TREATMENT The waste water treatment is carried out in three stages:- a)Primary treatment b)Secondary treatment c)Tertiary treatment

8. PRIMARY TREATMENT The primary treatment is used for removing the following :- Large settable solid Fat, oil and greases Sand , gravel and rocks Floating materials Primary treatment of sewage removes 60% suspended solids, 30% COD, 35% BOD, 10% P and 20% total nitrogen .

9. Primary treatment Process involved:- Screening Comminuting Grit removal Skimming tank sedimentation Floatation neutralization

10. screening Screening is the first operation at any wastewater treatment works. This process essentially involves the removal of large non-biodegradable and floating solids that frequently enter a wastewater works, such as rags, papers, plastics, tins, containers and wood. Wastewater screening is generally classified into a) coarse screening- Coarse screens are typically used as primary protection devices, and usually have openings of 10mm or larger. b) Fine screens - are used to remove material that may cause operation & maintenance problems in downstream processes, particularly in systems that lack primary treatment.

11. Typical opening sizes for fine screens are 3 to 10mm. With advances in screening technology, fine screens with openings of less than 3mm are now utilized to reduce suspended solids to levels near those achieved by primary clarification. Most modern wastewater treatment plants will utilize a combination of coarse and fine screening (i.e. upstream coarse screens providing protection to downstream fine screens ) SCREEN USED IN TREATMENT PROCESS

12. II. COMMINUTING Comminuting devices are shredders which incorporate mechanisms that cut the retained material without removing it from the sewage flow. However; solids from a Comminutors produce more scum at the digesters. Comminutors are generally located between grit chambers and the primary settling tanks

13. III. GRIT REMOVAL Grit includes sand, gravel, cinder, or other heavy solid materials that are “heavier” (higher specific gravity) than the organic biodegradable solids in the wastewater. Grit also includes eggshells, bone chips, seeds, coffee grounds, and large organic particles, such as food waste. Removal of grit prevents unnecessary abrasion and wear of mechanical equipment, grit deposition in pipelines and channels, and accumulation of grit in anaerobic digesters and aeration basins. Many types of grit removal systems exist, including aerated grit chambers, vortex-type , grit removal systems, detritus tanks , horizontal flow grit chambers and hydrocyclones.

14. Air is introduced in the grit chamber along one side, causing a perpendicular spiral velocity pattern to flow through the tank. Heavier particles are accelerated and diverge from the streamlines, dropping to the bottom of the tank, while lighter organic particles are suspended and eventually carried out of the tank

15. IV.SKIMMING TANK A skimming tank is a chamber so arranged that the floating matter like oil, fat, grease etc., rise and remain on the surface of the waste water (Sewage) until removed, while the liquid flows out continuously under partitions or baffles. It is necessary to remove the floating matter from sewage otherwise it may appear in the form of unsightly scum on the surface of the settling tanks or inter­fere with the activated sludge process of sewage treatment. It is mostly present in the industrial sewage. In ordinary sanitary sewage, its amount is usually too small. The chamber is a long trough shaped structure divided up into two or three lateral compartments by vertical baffle walls having slots for a short distance below the sewage surface and permitting oil and grease to escape into stilling compartments.

16. The rise of floating matter is brought about the blowing air into the sewage from diffusers placed in the bottom. Sewage enters the tank from one end, flows longitudinally and leaves out through a narrow inclined duct. A theoretical detention period of 3 minutes is enough. The floating matter can be either hand or mechanically removed. Grease traps are in reality small skimming tanks designed with submerged inlet and bottom outlet . The traps must have sufficient capacity to permit the sewage to cool and grease to separate.

17. V.sedimentation Sedimentation  is a physical water treatment process using gravity to remove suspended solids from water. Solid particles entrained by the turbulence of moving water may be removed naturally by sedimentation in the still water of lakes and oceans. Settling basins are ponds constructed for the purpose of removing entrained solids by sedimentation. Clarifiers are tanks built with mechanical means for continuous removal of solids being deposited by sedimentation.

18. VI. flotation Dissolved air flotation  ( DAF ) is a water treatment process that clarifies wastewaters by the removal of suspended matter such as oil or solids. The removal is achieved by dissolving air in the water under pressure and then releasing the air at atmospheric pressure in a flotation tank 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. Dissolved air flotation is very widely used in treating the industrial wastewater effluents from oil refineries, petrochemical and chemical plants. In the oil industry,  dissolved gas flotation  (DGF) units do not use air as the flotation medium due to the explosion risk.  Nitrogen gas is used instead to create the bubbles.

19. A typical dissolved air flotation unit (DAF) Modern DAF units using parallel plate technology are quite compact. The feed water to the DAF float tank is dosed with a coagulant (such as ferric chloride or aluminum sulfate) to coagulate the colloidal particles and/or a flocculants to conglomerate the particles into bigger clusters. 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. Bubbles form at nucleation sites on the surface of the suspended particles, adhering to the particles. As more bubbles form, the lift from the bubbles eventually overcomes the force of gravity. This causes the suspended matter to float to the surface where it forms 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.

20. VII.neutralization When pH of the industrial waste is too high or too low then it should be neutralized by acid or alkali and only neutral effluent should be discharged into drain. For neutralization of the acidic effluent , follow techniques are used:- Lime stone treatment Caustic soda treatment For neutralization of the alkaline effluent , following techniques are used:- Carbon dioxide treatment Sulphuric acid treatment Utilizing waste boiler- flue gas

21. Secondary treatment Secondary treatment is the portion of a sewage treatment sequence removing dissolved and colloidal compounds measured as biochemical oxygen demand (BOD). Secondary treatment is traditionally applied to the liquid portion of sewage after primary treatment has removed settleable solids and floating material. Secondary treatment is typically performed by indigenous, aquatic microorganisms in a managed aerobic habitat.  Bacteria and protozoa consume biodegradable soluble organic contaminants (e.g. sugars, fats, and organic short-chain carbon molecules from human waste, food waste, soaps and detergent) . Biological oxidation processes are sensitive to temperature and, between 0 °C and 40 °C, the rate of biological reactions increase with temperature. Most surface aerated vessels operate at between 4 °C and 32 °C.

22. Process involved in secondary treatment Activated sludge process Trickling filters Surface aerated lagoons

23. I. Activated sludge process The  activated sludge  process is a type of wastewater treatment process for treating sewage or industrial wastewaters using aeration and a biological floc composed of bacteria and protozoa. The process takes advantage of aerobic micro-organisms that can digest organic matter in sewage, and clump together (by flocculation) as they do so. It thereby produces a liquid that is relatively free from suspended solids and organic material, and flocculated particles that will readily settle out and can be removed.

24. Purpose of activated sludge process In a sewage (or industrial wastewater) treatment plant, the activated sludge process can be used for one or several of the following purposes: oxidizing carbonaceous matter: biological matter. oxidizing nitrogenous matter: mainly ammonium and nitrogen in biological materials. removing phosphate. driving off entrained gases carbon dioxide, ammonia, nitrogen, etc. generating a biological floc that is easy to settle.

25. The general arrangement of an activated sludge process for removing carbonaceous pollution includes the following items: Aeration tank where air (or oxygen) is injected in the mixed liquor. Settling tank (usually referred to as "final clarifier" or "secondary settling tank") to allow the biological flocs (the sludge blanket) to settle, thus separating the biological sludge from the clear treated water. Treatment of nitrogenous matter or phosphate involves additional steps where the mixed liquor is left in anoxic condition (meaning that there is no residual dissolved oxygen).

26. Sludge treatment Sewage sludge treatment  describes the processes used to manage and dispose of sewage sludge produced during sewage treatment. Sludge is mostly water with lesser amounts of solid material removed from liquid sewage. Primary sludge includes settleable solids removed during primary treatment in primary clarifiers. Secondary sludge separated in secondary clarifiers includes treated sewage sludge from secondary treatment bioreactors Sludge treatment is focused on reducing sludge weight and volume to reduce disposal costs, and on reducing potential health risks of disposal options. Water removal is the primary means of weight and volume reduction, while  pathogen  destruction is frequently accomplished through heating during thermophilic digestion,  composting , or incineration.

27. II.Trickling filters A  trickling filter  is a type of wastewater treatment system. It 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 (biofilm) 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 .

28. Typically, sewage flow enters at a high level and flows through the primary settlement tank. The supernatant from the tank flows into a dosing device, often a tipping bucket which delivers flow to the arms of the filter. The flush of water flows through the arms and exits through a series of holes pointing at an angle downwards. This propels the arms around distributing the liquid evenly over the surface of the filter media. Most are uncovered and are freely ventilated to the atmosphere. The removal of pollutants from the waste water stream involves both absorption and adsorption of organic compounds and some inorganic species such as nitrite and nitrate ions by the layer of microbial bio film. The filter media is typically chosen to provide a very high surface area to volume. Typical materials are often porous and have considerable internal surface area in addition to the external surface of the medium. Passage of the waste water over the media provides dissolved oxygen which the bio-film layer requires for the biochemical oxidation of the organic compounds and releases carbon dioxide gas, water and other oxidized end products. As the bio film layer thickens, it eventually sloughs off into the liquid flow and subsequently forms part of the secondary sludge.

29. The bio-film that develops in a trickling filter may become several millimeters 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 . This is very different from many other bio-films which may be less than 1 mm thick. Within the thickness of the biofilm both aerobic and anaerobic zones can exist supporting both oxidative and reductive biological processes. At certain times of year, especially in the spring, rapid growth of organisms in the film may cause the film to be too thick and it may slough off in patches leading to the "spring slough

30. III.Surface aerated lagoons An  aerated lagoon  (or  aerated pond)  is a simple wastewater treatment system consisting of a pond with artificial aeration to promote the biological oxidation of wastewaters. There are many other aerobic biological processes for treatment of wastewaters, for example activated sludge, trickling filters, rotating biological contactors . They all have in common the use of oxygen  and microbial action to reduce the pollutants in wastewaters.

31. Suspension mixed lagoons, where there is less energy provided by the aeration equipment to keep the sludge in suspension. Facultative lagoons, where there is insufficient energy provided by the aeration equipment to keep the sludge in suspension and solids settle to the lagoon floor. The biodegradable solids in the settled sludge then degrade as in an anaerobic lagoon.

32. TERTIARY TREATMENT Tertiary treatment, also referred to as effluent polishing, is carried out to improve water quality. Tertiary processes include filtration lagooning nutrient removal disinfection

33. A) FILTRATION Filtration is a common method of tertiary treatment, with either sand or activated carbon used to filter wastewater. The water is passed through a bed of sand or charcoal, allowing particulate matter in the water to adhere to the filter medium, removing it from the water. B)LAGOONING It is a method in which water is stored for some time in man-made ponds . During this process, plants and invertebrate animals which live in the water improve water quality by ingesting remaining particulate matter .

34. C)NUTRIENT REMOVAL In some locations, high levels of nutrients such as phosphorous and nitrogen must be removed from the wastewater before it can be released into the environment. This is important because if these nutrients are not removed from the water, they can provoke large-scale outgrowth of algae, causing ecosystem imbalance. Nutrient removal is performed by bacteria present in the wastewater, which convert the nutrients into forms that can be removed from the water. D) DISINFECTION The final tertiary process to be performed is disinfection, which is typically carried out with the addition of chlorine to wastewater. This process is used to kill microorganisms present in the water, to reduce the environmental impact of the waste . Water chlorination is one of the most common forms of disinfection, as it is an inexpensive and relatively simple process .