Sewage Treatment Plants.pptx

Sewage Treatment Plants

1. SEWAGE TREATMENT PLANT – A PERSPECTIVE by V i s h a l Du gg a l P A T IA L A (P u njab ) Ph . : 98 140 59 3 3 , 9 8 7 6 6 5 9 3 3 Email: [email protected], [email protected] f or Training Program Operation and Maintenance of Wastewater Treatment Plants (ETPs/CETPs/STPs) NATIONAL PRODUCTIVITY COUNCIL New Delhi

2. SEWAGE ( domestic sewage/domestic wastewater/municipal wastewater ) A type of wastewater that is produced by a community of people Consists of wastewater discharged from residences and from commercial, institutional and public facilities that exist in a locality Greywater : from sinks, bathtubs, showers, dishwashers, and clothes washers (reject water having lesser organic pollution load) Blackwater : the water used to flush toilets, combined with the human waste that it flushes away, and kitchen wastewater (reject water having higher organic pollution load)

3. POLLUTANTS Oxygen Demanding substances Biochemical Oxygen Demand, or BOD: Organic matter and ammonia are “oxygen-demanding” substances Demand is placed on the dissolved oxygen of the receiving waters by the microbial population in an effort to consume them as food Nutrients Carbon, nitrogen, and phosphorus are essential to living organisms and are the chief nutrients present An excess of these nutrients overstimulates the unwanted growth of aquatic plants, causes unsightly conditions, interferes with drinking water treatment processes, and causes unpleasant and disagreeable tastes and odours

4. POLLUTANTS… Inorganic and recalcitrant organic substances A vast array of chemicals Many of these substances are toxic to life and are also harmful to humans May be poisonous at very low concentrations Pathogens Infectious micro-organisms, or pathogens Causes the occurrence of waterborne diseases Suspended solids Insoluble matter present May be inert Can cause deposits, chokings, anaerobic conditions

5. RAW SEWAGE CHARACTERISTICS

6. TYPICAL CHARACTERISTICS Parameter Average quantity a) BOD 3 , 27  C 200-250 mg/l b) COD 300-400 mg/l c) Total suspended solids 400-500 mg/l d) Total dissolved solids 800-1500 mg/l e) Total kjeldahl nitrogen (as N) 30-45 mg/l f) Total phosphorus (as P) 5-15 mg/l g) Feacal coliform count 1 x 10 7 MPN/100 ml h) Soluble fraction of BOD 55-60%

7. TREATED SEWAGE STANDARDS Parameter Average quantity a) pH 6.5-8.5 b) BOD 3 , 27  C <10 mg/l c) COD <50 mg/l d) Total suspended solids <10 mg/l e) Ammoniacal nitrogen (as N) <5 mg/l f) Total nitrogen (as N) <10 mg/l g) Feacal coliform count <100 MPN/100 ml

8. TREATMENT REQUIREMENTS Preliminary treatment Removes materials that can cause operational problems Primary treatment Typically meant to remove ~60% of suspended solids and ~35% of BOD Secondary treatment Typically meant to remove ~85% of BOD and suspended solids Advanced treatment Typically meant to remove >85% of BOD, solids, and nutrients Final treatment (polishing) – disinfection Solid management – sludge handling

9. TYPICAL P.F.D. OF AN S.T.P.

10. RAW SEWAGE PUMPING Receiving chamber Coarse screening Wet well (raw sewage sump) Pump house Raw sewage pumps

11. PUMPING STATION CONFIGURATIONS

12. PRIMARY TREATMENT Screening Objective: Removal of coarse solids Types of screens: Fine/medium/coarse Cleaning of screens: Manual/mechanical Benefits: Protection of pumps Coarse Screening: 20 mm clear spacing in bars Fine screening: 6 mm clear spacing in bars

13. PRIMARY TREATMENT (SCREENING)

14. PRIMARY TREATMENT (SCREENING)

15. PRIMARY TREATMENT Grit removal Objective: Removal of inorganic solids, e.g., pebbles/sand/ silt to protect moving mechanical equipment Principle: Gravity separation (effective size – 0.15 mm; specific gravity – 2.65) Types: Manual grit removal – Rectangular channel Mechanical grit removal - Circular tank Grit removal mechanism: Screw classifier/reciprocating classifier

16. PRIMARY TREATMENT (GRIT REMOVAL)

17. PRIMARY TREATMENT (GRIT REMOVAL)

18. PRIMARY TREATMENT (GRIT REMOVAL)

19. SECONDARY TREATMENT The microorganisms are cultivated in the wastewater. The microorganisms use organic matter from sewage as their food supply. This process leads to decomposition or biodegradation of organic wastes. Activated Sludge Process (ASP) Up-flow Anaerobic Sludge Blanket Reactor (UASBR) Moving Bed Biofilm Reactor (MBBR) Sequential Batch Reactor (SBR) Membrane Bio-reactor (MBR) Lagoons/stabilisation ponds Constructed wetland systems

20. SECONDARY TREATMENT High density of microorganisms – keep organisms in system Good contact between organisms and wastes – provide mixing Provide high levels of oxygen (for aerobic processes) - aeration Favorable temperature, pH, nutrients – design and operation No toxic chemicals present – control or pre-treat inputs

21. ACTIVATED SLUDGE PROCESS Proven and tested for more than 7 decades all over world Several modifications/advances possible to meet specific requirements Comprises of; Aeration tank containing micro organisms in suspension in which reaction takes place. Activated sludge recirculation system. Excess sludge wasting and disposal facilities. Aeration systems to transfer oxygen Secondary sedimentation tank to separate and thicken activated sludge. Performance is critically dependent on sludge settling characteristics and design of secondary clarifier

22. ACTIVATED SLUDGE PROCESS… Sludge settling characteristics are typically influenced by bio-flocculation which in turn depends on growth rate of micro-organisms Growth rate is generally controlled by controlling biological solids retention time/food to micro-organism ratio Requires careful monitoring of the reactor sludge levels and sludge withdrawal

23. ACTIVATED SLUDGE PROCESS… Advantages Performance is not significantly affected due to normal variations in wastewater characteristics and seasonal changes Less land requirements Disadvantages High recurring cost High energy consumption Performance is adversely affected due to interruption in power supply even for a short period Foaming, particularly in winter season, may adversely affect the oxygen transfer, and hence performance Nitrogen and Phosphorous removal requires additional anoxic tank and >3 times internal recirculation More land requirement than SBR & MBBR

24. UPFLOW ANAEROBIC SLUDGE BLANKET 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 The upward flow combined with the settling action of gravity suspends the blanket with the aid of flocculants The sludge in the UASB is tested for pH, volatile fatty acids (VFA), alkalinity, COD and SS. If the pH reduces while VFA increases, the sewage should not be allowed into the UASB until the pH and VFA stabilise. The reactor may need to be emptied completely once in five years, while any floating material (scum) accumulated inside the gas collector channels may have to be removed every two years to ensure free flow of gas.

25. UPFLOW ANAEROBIC SLUDGE BLANKET REACTOR

26. UPFLOW ANAEROBIC SLUDGE BLANKET REACTOR Advantages Requires lesser power than aerobic processes Biogas generated can be used as fuel or electricity Disadvantages UASB alone does not treat the sewage to desirable limits, therefore downstream aerobic treatment is compulsory Requires very large space due to post treatment Recovery of biogas is not sufficient to produce substantial electricity in case of municipal wastewater

27. MOVING BED BIO-REACTOR A compact and robust system involving extended aeration process with submerged aeration Biomass growth on fluidized bed of plastic media enabling retention of biomass and long solid retention time in the reactor leading to low “food to micro-organism ratio” and higher organic removal Two stage biological oxidation The process is intended to enhance the activated sludge process by providing greater biomass in aeration tank and thus by reducing volume of the tank After aeration tank sedimentation tank is provided for settlement of sloughed biomass Ability to withstand limited organic overload

28. MOVING BED BIO-REACTOR Special grade plastic proprietary media custom made for offering high specific surface area is required MBBR is a unique process in which combines suspended as well as attached growth principles of biological wastewater treatment The biomass responsible for the removal of organic matter from the wastewater is held in suspension as well as on the bio carriers provided in the reactor as fixed film MBBR provides an unique combination of advantages provided by both activated sludge system as well as fixed film system and at the same time trying to minimize the drawbacks of both the systems In MBBR, the biological performance is independent of solids separations

29. MOVING BED BIO-REACTOR

30. MOVING BED BIO-REACTOR

31. MOVING BED BIO-REACTOR Advantages Requires lesser space Ability to effectively treat dilute domestic wastewaters Elimination of the need for sludge recirculation and monitoring of MLSS in the reactor Capacity to handle shock loads Low and stabilised sludge production Simple and reliable operation Disadvantages Control of SRT and other process parameters is difficult Problems of choking of media Problems of media loss

32. SEQUENTIAL BATCH REACTOR (S.B.R.) The sequencing batch reactor (SBR) is a fill-and-draw type activated sludge system operating in batch The treatment consists of a cycle of five stages: fill, react, settle, draw and idle. During the reaction type, oxygen is added by an aeration system. The bacteria oxidise the organic matter just as in activated sludge systems. Thereafter, aeration is stopped to allow the sludge to settle. Then the water and the sludge are separated by decantation and the clear layer (supernatant) is discharged from the reaction chamber through a special decanter Depending on the rate of sludge production, some sludge may also be purged

33. SEQUENTIAL BATCH REACTOR (S.B.R.) After a phase of idle, the tank is filled with a new batch of wastewater At least two tanks are needed for the batch mode of operation as continuous influent needs to be stored during the operation phase. It performs biological organic removal, nitrification, de-nitrification and biological phosphorous removal.

34. SEQUENTIAL BATCH REACTOR (S.B.R.)

35. SEQUENTIAL BATCH REACTOR (S.B.R.) Advantages Controls growth of filamentous bacteria and avoids bulking of sludge Provides stabilised sludge. Allows for easy modular expansion for increased flow High BOD removal of up to 98% Disadvantages Compared to the conventional ASP/MBBR/UASB, a higher level of sophistication and maintenance is associated due to automation The SBR is susceptible to shock loads Process start-up stabilisation require very high skills

36. MEMBRANE BIO REACTOR (M.B.R.) Combines membrane technology with biological treatment Replaces conventional clarification, aeration and filtration into a single step The use of membrane filtration allows an MBR process to produce a significantly higher quality effluent than that obtainable from a conventional aerobic treatment process The mixed liquor suspended solids concentration (MLSS) and the solids retention time (SRT) are limited in a other aerobic processes The MLSS and SRT can both be larger for MBR processes This results in a smaller aeration tank volume needed for an MBR process than that needed for other aerobic processes

37. MEMBRANE BIO REACTOR (M.B.R.)

38. MEMBRANE BIO REACTOR (M.B.R.)

39. MEMBRANE BIO REACTOR (M.B.R.) Advantages Better effluent quality, smaller space requirements, and ease of automation Operate at higher volumetric loading rates which result in lower hydraulic retention times The low retention times mean that less space is required compared to a conventional system. The treated effluent contains low concentrations of bacteria, TSS, BOD, and phosphorus. This facilitates high-level disinfection. High quality water produced for effective reuse

40. MEMBRANE BIO REACTOR (M.B.R.) Disadvantages Very high level of sophistication and maintenance is associated Higher capital and operating costs Problem of membrane fouling and choking drastically reduces plant efficiency Very high operational complexity – require highly skilled manpower for operation

41. STABILISATION POND Wastewater Stabilization Ponds (WSPs) are large, man-made water bodies in which blackwater, greywater or faecal sludge are treated by natural occurring processes and the influence of solar light, wind, microorganisms and algae The ponds can be used individually, or linked in a series for improved treatment Three types of ponds: anaerobic, facultative, aerobic (maturation), each with different treatment and design characteristics WSPs are low-cost for O&M and BOD and pathogen removal is high Very large surface areas are required The treated effluent is appropriate for the reuse in agriculture only

42. STABILISATION POND

43. STABILISATION POND Advantages Simple to construct, operate and maintain Does not involve installation of expensive electro-mechanical equipment Has very low O&M costs Extremely robust and can withstand hydraulic and organic shock loads BOD reduction of the order of 90% and more Coliform reduction could be up to 6 log units High quality effluent at least operating costs Low skill requirement for operation of the plant

44. STABILISATION POND Disadvantages Very large land requirement High cost of lining Likelihood of odour nuisance and mosquito breeding in poorly maintained WSPs If unlined, likelihood of groundwater contamination in porous and fractured strata

45. SLUDGE HANDLING Involves sludge dewatering Sludge drying beds Conventional method of sludge drying No power requirement Substantial area is required Difficult to operate in monsoon Labour intensive Manual scrapping and loading of dried sludge

46. SLUDGE HANDLING

47. SLUDGE HANDLING Mechanical dewatering – centrifuge Advanced method of solid-liquid separation Less area Power required for pumping the sludge and operation of centrifuge Less time Efficient dewatering

48. SLUDGE HANDLING

49. COMMON PROBLEMS & TROUBLESHOOTING Treated effluent is not meeting total nitrogen targets Analyse for Ammonia, Nitrite and Nitrate In case of high ammonia look to ensure your plant has the following; Generally, nitrification occurs only under aerobic conditions at dissolved oxygen levels of more than 1.0 mg/L Nitrification requires a long retention time A low food to microorganism ratio (F:M) A high mean cell residence time (measured as MCRT or Sludge Age) Adequate pH buffering (alkalinity)

50. COMMON PROBLEMS & TROUBLESHOOTING Treated effluent is not meeting total nitrogen targets The biological reduction of nitrate to nitrogen gas is performed by bacteria that live in a low-oxygen environment. To thrive, the bacteria need biochemical oxygen demand (BOD) – soluble BOD. Adequate carbon source: about five times as much as the amount of nitrate being denitrified Ensure that the nitrification process is working otherwise there will be no nitrate to denitrify Ensure that the anoxic tank has 0 DO. Otherwise Mixed Liquor Return Rate (MLR) might need to be reduced (as a rule of thumb this flow rate is usually set at 300% of the daily incoming flow)

51. COMMON PROBLEMS & TROUBLESHOOTING Treated effluent is not meeting BOD targets High effluent BOD levels in the treated effluent can have a number of causes Incomplete wastewater treatment due to organic overloading Low oxygen concentration Low hydraulic detention time Physical short circuiting High algae or sulphur bacteria growth Sludge accumulation and loss of old sludge to the effluent

52. COMMON PROBLEMS & TROUBLESHOOTING Sludge overflow from clarifier This phenomenon may be related to oxygen deficiency or nutrient deficiency. It can also be adversely affected by the long residence time in sedimentation tanks when denitrification bacteria can start to produce nitrogen gas Also not sufficient sludge removal from the system might be a reason of those problems

53. Any Questions …….???