Sewage Treatment and waste disposal.pptx

Sewage Treatment and waste disposal

1. Sewage Treatment & Waste disposal Dr Khem R Sharma SPH&CM

2. Introduction An inevitable and inherent product of social, economic and cultural life that is unwanted and undesirable. Domestic Waste is either solid or liquid (sewage) generated in residential areas, Commercial settings and institutions. The indiscriminate disposal of waste adversely affects the immediate human environment and possess health risk to exposed population that is carried through different vehicles including flies, dogs, rodents.

3. Public Health importance of waste It decomposes and favors fly breeding. Can contaminate food supply and cause food borne disease. It attracts rodents and other animals e.g. rats mice dogs cats. Water and soil pollution. An unsightly appearance, bad odors, nuisance. Incidence of vector- borne diseases.

4. Sewage Sewage is waste water from a community containing solid and liquid excreta, derived from houses, street and yard washings, factories and industries. “Sullage" is applied to waste water which does not contain human excreta, like waste water from kitchens and bathrooms. The amount of sewage that flows in the sewers depends upon: (a) Habits of the people & (b) Time of day Amount of sewage which flows through the sewerage system in 24 hours is called the "dry weather flow."

5. Composition of sewage Sewage contains 99.9 % of water. The solids comprise barely 0.1 % and are partly organic and inorganic; they are partly in suspension and partly in solid. Offensive nature of the sewage - due to organic matter that it contains which gives off offensive odours when it decomposes. Sewage contains numerous living organisms derived from faeces , some of which may be agents to disease. Estimate: one gram of faeces may contain about 1,000 million E coli, 10 to 100 million of faecal streptococci, and 1 to 10 million spores of Cl. perfringens besides several others.

6. Aims of Sewage Treatment When raw/inadequately treated sewage is discharged into rivers, sea or other sources of drinking water, the oxygen in the water supply is used up by the numerous aerobic bacteria found in the sewage. Depletion of oxygen may lead to the death of the plant and animal life in water and an offensive smell could develop due to the release of hydrogen sulphide . The aim of sewage treatment is to "stabilize" the organic matter so that it can be disposed off safely; and, to convert the sewage water into an effluent of an acceptable standard of purity which can be disposed off in to land, river or the sea.

7. Decomposition of organic matter The decomposition of organic matter in sewage takes place by two processes - aerobic and anaerobic. Aerobic Process - most efficient method of reducing the organic matter in sewage. The process requires a continuous supply of free dissolved oxygen. The organic matter is broken down into simpler compounds namely CO2, water, ammonia, nitrites, nitrates and sulphates by the action of bacterial organisms including fungi and protozoa. Anaerobic Process : Where the sewage is highly concentrated and contains plenty of solids, the anaerobic process is highly effective. -The end-products of decomposition are methane, ammonia and CO. -In anaerobic decomposition, the reactions are slower and the mechanism of decomposition extremely complex.

8. Standard Tests The organic content of the sewage and its "strength“ is expressed in terms of BIOCHEMICAL OXYGEN DEMAND (BOD): most important test done on sewage. - amount of oxygen absorbed by a sample of sewage in a specified period (5 days), at a specified temperature(20 deg.C ) for the aerobic destruction of organic matter by living organisms - values range from 1mg/ litre (natural waters) to 300 mg/ litre for domestic sewage. - BOD ≥ 300 mg/l, sewage is said to be "strong"; if it is 100 mg/I, it is said to be "weak" CHEMICAL OXYGEN DEMAND (COD): measures oxygen equivalent of that portion of the organic matter in a sample which is susceptible to oxidation by a strong chemical oxidiser . - If wastes contain toxic substances, this test may be the only practical method for determining the organic load. SUSPENDED SOLIDS: yet another indicator of the "strength" of sewage. -Amount of suspended solids in sewage may vary from 100 to 500 p.p.m. (mg/l). -If the amount of suspended solids is 100 mg/I, the sewage is weak; if the amount is 500 mg/l the sewage is said to be strong.

9. Modern sewage treatment plant flow diagram

10. Primary Treatment Screening Sewage first passes through a metal screen that intercepts large floating objects such as pieces of wood, rags, garbage mass and dead animals - necessary to prevent clogging of the treatment plant. Grit chamber Allows the settlement of heavier solids such as sand/gravel, while permitting the organic matter to pass through. The grit which collects at the bottom of the chamber is removed periodically/continuously, and disposed off by plain dumping or trenching.

11. Primary Treatment…. Primary sedimentation Sewage is now admitted into a very large tank (primary sedimentation tank) where it flows very slowly across the tank (1- 2 feet/minute) and spends about 6-8 hours in the tank. Nearly 50-70 per cent of the solids settle down due to gravity by sedimentation of suspended matter along with a 30-40% reduction in the number of coliforms.

12. Sludge is the organic matter which settles down that is removed by mechanically operated devices without disturbing the operation in the tank. Biological action also takes place where the microorganisms attack complex organic solids & break them down into simpler soluble substances and ammonia. Scum is the fat and grease which rise to the surface which is removed from time to time and disposed of. Primary Treatment….

13. Secondary Treatment Primary sedimentation tank effluent still contains organic matter in solution/colloidal state along with numerous living organisms that has a high demand for oxygen and can cause pollution of soil or water. It is subjected to further, aerobic oxidation treatment by one of the following methods : Trickling filter method Activated sludge process.

14. (a) Trickling Filter Method The effluent from the primary sedimentation tank is sprinkled uniformly on the surface of trickling/ percolating filter (bed of crushed stones) by a revolving device. “Zoogleal layer" is a very complex biological growth consisting of algae, fungi, protozoa and bacteria that oxidize the effluent making the filtration a biological process and not a mechanical one. The trickling filters are very efficient in purifying sewage as air passes freely supplying the oxygen needed by the zoogleal flora. The zoogleal layer lives, grows and dies and is washed down the filter as "humus“ while the oxidized sewage is passed through the secondary sedimentation tanks or humus tanks.

15. (b) Activated Sludge Process Modern method of purifying sewage that uses less space, but requires skilled operations (1 acre of activated sludge plant does the work of 10 acres of percolating filter) best suited for larger cities.

16. Secondary sedimentation The oxidized sewage from the trickling filter/aeration chamber is led into the secondary sedimentation tank where it is detained for 2-3 hours. The sludge that collects in the secondary sedimentation tank is called 'aerated sludge’/activated sludge, because it is fully aerated and is a valuable manure, if dehydrated. Part of the activated sludge is pumped back into the "aeration tanks" in the activated sludge process and the rest pumped into the sludge digestion tanks for treatment and disposal.

17. Sludge treatment and disposal Thick, black mass containing 95% water with a revolting odour which is a problem associated with sewage treatment. Digestion : Modern sewage treatment plants incubate sludge under favourable conditions of temperature and pH to undergo anaerobic auto-digestion with release of water, carbon dioxide, methane and ammonia (3-4 weeks or longer). The residue is in-offensive, sticky and tarry mud which forms excellent manure. Methane gas, a by-product of sludge digestion - heating and lighting purposes. Sea disposal: Sea coast towns/cities can pumping it into the sea’. Land : Sludge can be disposed of by composting with town refuse.

18. Disposal of effluent Disposal by dilution: Disposal into water courses such as rivers and streams where the impurities are oxidized by the dissolved oxygen in water after it is rendered free from pathogenic organisms by adequate chlorination. Disposal on land: If suitable land is available the effluent can be used for irrigation purposes

19. Other Methods of Sewage Disposal Sea outfall River outfall Land treatment Oxidation ditches Oxidation ponds

20. Other Methods of Sewage Disposal….. Sea outfall Sea coastal cities dispose of their sewage by discharging it into the sea where purification takes place by dilution in the large body of sea water and the solids get slowly oxidized. (2/3 of untreated sewage of Greater Mumbai is discharged into the Arabian Sea every day) The drawback is offensive solid matter may be washed back to the shore and create public nuisance to prevent which, the sewage outfall is designed to discharge the sewage into deep water at many points. River outfall Raw sewage should never be discharged into rivers but the present day practice is to purify the sewage before it is discharged into rivers.

21. Land treatment (sewage farming) Sufficient and suitable land (porous soil) is first laid into ridges and furrows, and sewage, after grit removal, screening and a short period of settlement, is fed into the furrows intermittently and crops are grown on the ridges and do not come in contact with the sewage. Oxidation ditches/aerated lagoons. These methods make use of mechanical rotors for extended aeration and are low-cost treatment methods for the purification of sewage. Other Methods of Sewage Disposal…..

22. Oxidation pond (waste stabilization pond, sewage lagoon) A cheap method of disposal for both sewage and industrial wastes for small communities. The oxidation pond is an open, shallow pool with the presence of algae, bacteria that feed on decaying organic matter, and sun-light. The organic matter contained in the sewage is oxidized by bacteria to simple chemical compounds such as CO2, ammonia and water, while the algae utilize the CO2, water and inorganic minerals for their growth with the help of sunlight and liberate oxygen . Predominantly aerobic during sunshine hours as well as some hours of the night but the bottom layers are generally anaerobic in the remaining hours of the night. Other Methods of Sewage Disposal…..

23. Solid waste management A systematic administration of activities that provide for the collection, source separation, storage, transportation, transfer, processing, treatment and disposal of solid waste. “Solid wastes” includes - Garbage (food wastes), - Rubbish (paper, plastics, wood, metal, throwaway containers, glass), - Demolition products (bricks, masonry, pipes), - Sewage treatment residue, - Dead animals, manure and other discarded material.

24. Solid waste management…. The output of daily waste depends upon the Dietary habits, Life styles, Living standards The degree of urbanization and industrialization. The solid waste produced ranges between 0.25 to 2.5 kg in different countries.

25. Classifications of solid waste Organic solid waste: Wastes that are generally biodegradable and decompose in the process of which emits offensive and irritating smell when left unattended Inorganic solid waste: Solid matter that does not decompose at any rate. This category of waste matter may be combustible depending on the type of the nature of the material they constitute

26. Composition of Solid Waste in the KMC

27. Solid waste management…. There are six functional elements in the activities associated with the management of solid wastes from the point of generation to final disposal site. Waste generation On-site handling (sorting, storage and processing) Collection Transfer and transport Processing and recovery Disposal

28. Functional elements and its Interrelationships in the solid waste management system

29. I. Waste generation - Sources of refuse

30. II. Waste handling and separation, storage and processing at the source The best place to separate waste materials for reuse and recycling is at the source of generation Waste processing is used to reduce the volume, recover usable materials, and alter the physical form of the solid wastes. ⇒ The most common on-site processing operations used are: - Food waste grinding and release to sewer system - Component separation - Compaction: decrease the volume up to 70% - Incineration, yard waste composting etc

31. III. Waste Collection Conducted under various management pattern/arrangements: Municipal/Rural Communities Organization Private services such as contractors Scavenger system: Individuals may collect and use wastes like paper, metal, containers, clothes etc for reuse or recycling.

32. Waste Collection… The KMC has been applying following methods to collect household wastes: Door to door collection Vehicle collection Roadside based collection

33. Waste Management… Transfer and transport: Those activities associated with the transfer of wastes from the smaller collection vehicle to a larger transport equipment and the subsequent transport of the wastes, usually over long distance, to the disposal site. Processing and recovery: Those techniques equipment and facilities used both to improve the efficiency of the other functional elements and to recover useable materials, conversion products, or energy from solid wastes.

34. Recycling and Reuse Different ways and practices of converting wastes into useful assets exist. Human/animal urine contains nitrogen that is used as fertilizer. Farmers in rural Ethiopia use manure and other waste as fertilizers. Animal bones can be used as a very important animal feed after processing. Rural communities know and use dung for plastering of houses and as an energy source for open fire burning. In general, waste recovery and reuse is economically and socially feasible and acceptable.

35. VI. Methods of Disposal The methods of waste disposal are: Dumping Controlled Tipping or Sanitary Land-fill Incineration Composting Manure Pits Burial

36. a) Dumping Refuse is dumped in low lying areas where as a result of bacterial action, refuse decreases considerably in volume and is converted gradually into humus. Three methods are used: The trench method: Where leveI ground is available. The ramp method: Moderately sloping terrain. The area method: For filling land depressions, disused quarries and clay pits. It takes 4 to 6 months for complete decomposition of organic matter into an innocuous mass.

37. Drawbacks of Dumping The refuse is exposed to files and rodents. Drainage from dumps contributes to the pollution of surface and ground water. A WHO Expert Committee (1967) condemned dumping as “ a most insanitary method that creates public health hazards, a nuisance, and severe pollution of the environment”.

38. b) Controlled Tipping/ Sanitary Landfill In this method a big hole is dug in an area which is not near water sources, houses or near a road/path. Waste generated every day is dumped into the pit and covered with earth so that flies and vermin don't get access to it. The process continues until the pit is filled after which it should be completely covered with earth and another one is dug next to the old one. The decomposable waste will still condition the soil, so crops planted on completed sites grow better.

39. c) Incineration Incineration is a high temperature dry oxidation process that reduces organic and combustible waste to inorganic, incombustible matter resulting in a very significant reduction of waste volume and weight. This process is not quite environmentally friendly due to the generation of greenhouse gases such as carbon dioxide and carbon monoxide Characteristics of wastes suitable for incineration: Content of combustible matter above 60% Content of non-combustible solids below 5% Moisture content below 30%

40. d) Composting Method of combined disposal of refuse and night-soil or sludge. Organic matter breaks down under bacterial action resulting in the formation of relatively stable humus-like material, called the compost which has considerable value as manure for the soil with carbon dioxide, water and heat as by-products. The following methods of composting are now used : Bangalore method (Anaerobic method) Mechanical composting (Aerobic method)

41. e) Manure Pits The problem of refuse disposal in rural areas can be solved by digging 'manure pits' by the individual households. The garbage, cattle dung, straw, and leaves should be dumped into the manure pits and covered with earth after each day‘s dumping. Two such pits will be needed, when one is closed, the other will be functional In 5 - 6 month's time, the refuse is converted into manure which can be returned to the field.

42. f) Burial This method is suitable for small camps. A trench 1.5 m wide and 2 m deep is excavated, and at the end of each day the refuse is covered with 20 to 30 cm of earth. When the level in the trench is 40 cm from ground level, the trench is filled with earth and compacted, and a new trench is dug out.

43. Health Care Waste Management The waste produced in the course of health-care activities carries a higher potential for infection and injury than any other type of waste. Incineration Chemical disinfection Wet and dry thermal treatment Microwave irradiation Land disposal lnertization

44. HCW Categorization in Nepalese context The final choice of method should be made on the basis of factors, many of which depend on local conditions. Non-risk HCW should at least be separated into: Bio-degradable Non-biodegradable Risk health care wastes should at least be separated into six categories as mentioned below: Pathological Waste d) Cytotoxic waste Infectious waste e) Pharmaceutical waste Sharp waste f) Other hazardous waste

45. Best Wishes Best Wishes