Part II Sanitary Systems - PowerPoint Presentation

1. Part II Sanitary SystemsChapter 2C : Type of Treatment System Geremew Sahilu (PhD)/ Abstracted from Dr. Agizew’s Presentation for MoWIE Training

2. Goals of Wastewater TreatmentWastewater is 99-99.9% water and 0.1-1% solids. The main task in treating the wastewater is simply to remove the solids.Stabilization of the solids Proper reuse/disposal Ultimate purposes:Protecting public healthProtecting the environment

3. WWT Feasibility Study Components Design horizon (e.g. 20 years) and staging periods (e.g. 7-10 years)Influent quantity and quality characterizationWastewater treatment objectives and effluent quality requirementsSite selection for WWTPInitial screening of WWT alternativesPreliminary design of the promising alternatives (sizing of units, power, equipment and resource requirements, process flowsheet, plant layout, sludge management)Economic evaluation of alternativesESIASelection of alternative for further detail design

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5. Wastewater Treatment Levels

6. Common Treatment Operations and Processes for Removal Pollutants from Sewage

7. Generalized WWT Flow Diagram

8. Preliminary TreatmentRemoves large objects and non-degradable materialsProtects pumps and equipment from damage

9. Preliminary Treatment- Screening Objective Removal of course solidsTypes of screensFine/medium/coarseCleaning of screensManual/mechanicalBenefits Protection of pumpsCoarse screening 20mm clear spacing in barsFine screening 60mm clear spacing in bars

10. Preliminary Treatment- Grit Removal Objective Removal of inorganic solids like sand to protect moving mechanical equipmentPrinciple Gravity separation: effective size 0.15mm; specific gravity- 2.65Types Manual- Rectangular channelMechanical- Circular tankGrit removal mechanism Screw classifier/reciprocating classifier

11. Primary TreatmentWastewater flow is slowed down and suspended solids settle to the bottomReduces the suspended solids and the B.O.D. of the wastewater

12. Efficiency of Primary Clarifier 0102030405060708090100012345Residence time HRT (h)Efficiency (%)settleable solidsTSSBOD5

13. Typical Design Criteria for Primary Sedimentation Basins

14. Typical Design Criteria for Primary Sedimentation Basins

15. Biological TreatmentObjectives of biological treatment:To stabilize the organic contentTo remove nutrients such as nitrogen and phosphorusTypes:Aerobic ProcessesAnoxic ProcessesAnaerobic ProcessesCombined Aerobic-Anoxic-Anaerobic ProcessesPond ProcessesAttached GrowthSuspended Growth Combined SystemsAerobic MaturationFacultativeAnaerobicAerobicAnaerobic

16. Examples of Treatment TechnologiesSuspended growthAttached growthDual biologicalActivated sludgeStabilization pondsAerated lagoonsContainment pondsConstructed wetlandsPlug flowComplete mixOxidation ditchContact stabilizationSequencing batch reactorsConventional Extended aeration High rateStep feedTapered aerationTrickling filtersBiotowersRotating biological contactors16

17. Major Aerobic Biological ProcessesType of GrowthCommon NameUseSuspended GrowthActivated Sludge (AS)Carbonaceous BOD removal (nitrification)Aerated LagoonsCarbonaceous BOD removal (nitrification)Attached GrowthTrickling FiltersCarbonaceous BOD removal. nitrificationRoughing Filters (trickling filters with high hydraulic loading rates)Carbonaceous BOD removalRotating Biological ContactorsCarbonaceous BOD removal (nitrification)Packed-bed reactorsCarbonaceous BOD removal (nitrification)Combined Suspended & Attached Growth Activated Biofilter ProcessTrickling filter-solids contact processBiofilter-AS processSeries trickling filter-AS process Carbonaceous BOD removal (nitrification)

18. Activated Sludge ProcessThe aeration tank contains a suspension of the wastewater and microorganisms, the mixed liquor. The liquor is mixed by aeration devices (supplying also oxygen)A portion of the biological sludge separated from the secondary effluent by sedimentation is recycled to the aeration tankAeration BasinAeration

19. Some Activated Sludge Configurations

20. CAS: Advantages/DisadvantagesAdvantageDisadvantage

21. Main characteristics of activated sludge systems

22. Biological Nitrogen removalBOD + NitrificationDenitrification Return nitrateReturn sludgeWASAnoxic tankMethanolInfluent Effluent Aerobic tankAeration WAS22Nitrification in aerobic environmentOrganic matter + O2  NH3 + CO2 + microorganismsNH3 + 2O2  NO3- + H+ + H2O + microorganisms Denitrification in an anoxic environment (no free oxygen)Organic matter + NO3-  N2 + microorganisms

23. Biological Nitrogen removalDenitrification BOD + NitrificationReturn nitrateReturn sludgeWASAnoxic tankAerobic tankSecondary clarifierInfluent Effluent 23

24. Design criteria for biological nitrogen removal

25. Two-stage biological P removalReturn sludgeWASAnaerobic tankAerobic tankSecondary clarifierInfluent Effluent 25

26. Trickling FiltersThe trickling filter or biofilter consists of a bed of permeable medium of either rock or plastic Microorganisms become attached to the media and form a biological layer or fixed film. Organic matter in the wastewater diffuses into the film, where it is metabolized. Periodically, portions of the film slough off the media

27. Advantages/Disadvantages AdvantagesGood quality (80-90% BOD5 removal) for 2-stage efficiency could reach 95% Moderate operating costs (lower than activated sludge)Withstands shock loads better than other biological processesDisadvantagesHigh capital costs Clogging of distributors or bedsSnail, mosquito and insect problems

28. Comparison of Different Types of Trickling Filters

29. Rotating Biological ContactorsIt consists of a series of circular disks of polystyrene or polyvinyl chloride that are submerged in wastewater and rotated slowly through itThe disk rotation alternately contacts the biomass with the organic material and then with atmosphere for adsorption of oxygenExcess solids are removed by shearing forces created by the rotation mechanism

30. RBC: Advantages/DisadvantagesAdvantagesShort contact periodsHandles a wide range of flowsEasily separates biomass from waste streamLow operating costs Short retention timeLow sludge productionExcellent process controlDisadvantagesNeed for covering units installed in cold climate to protect against freezingShaft bearings and mechanical drive units require frequent maintenance

31. Moving Bed BioreactorThe Moving Bed Bio Reactor (MBBR) process utilize the attached bio-film and provides smaller footprint solution for with lower capital and operating costs.The suspended biomass carriers are designed to create a large surface area for biofilm growth.Uses small, plastic elements to support the growth of biofilm in the reactorBenefits include:An enhanced biological wastewater treatment process without increasing the plant footprintMBBR process is ideally suited for retrofit/upgrade of existing installation with minimum changes in the existing setup.Typical design criteria:MLSS: 100 to 250 mg/LMCRT: 0.15 daysHRT: 3 hours

32. Membrane Bio-Reactor (MBR)A new method for wastewater treatment, integrates membrane separation and biotechnologyRejects activated sludge and macromolecular organic matter in aerobic tank/MBR tank with membrane separation plant, thus saving the use of secondary sedimentation tank.Consequently, the concentration of activated sludge rises greatly, the HRT and the SRT could be controlled separately, and difficult degraded matters are constantly degraded and reacting in reactor.Effluent quality MBR-AA

33. Advantages/Disadvantages of MBRs

34. Major Anaerobic Biological ProcessesType of GrowthCommon NameUseSuspended GrowthAnaerobic Contact ProcessCarbonaceous BOD removalUpflow Anaerobic Sludge-Blanket (UASB)Carbonaceous BOD removalAttached GrowthAnaerobic Filter ProcessCarbonaceous BOD removal, waste stabilization (denitrification)Expanded BedCarbonaceous BOD removal, waste stabilization

35. Anaerobic Contact ProcessUntreated wastewater is mixed with recycled sludge solids and then digested in a sealed reactorThe mixture is separated in a clarifier The supernatant is discharged as effluent, and settled sludge is recycled

36. ACP: Advantages/DisadvantagesAdvantagesMethane recoverySmall area requiredVolatile solids destructionDisadvantagesHeat requiredEffluent in reduced chemical form requires further treatmentRequires skilled operationSludge to be disposed off is minimal

37. Upflow Anaerobic Sludge Blanket Reactor

38. UASB: Upflow Anaerobic Sludge BlanketWastewater flows upward through a sludge blanket composed of biological granules that decompose organic matterSome of the generated gas attaches to granules that rise and strike degassing baffles releasing the gasFree gas is collected by special domesThe effluent passes into a settling chamber

39. Recommended Design Criteria for UASB

40. UASBAdvantagesRequires less power than aerobic processesBiogas genarated can be used as fuel or electricityDisadvantagesUASB alone does not treat the sewage to desirable limits; therefore, downstream aerobic treatment is compulsoryRequires very large space due to post treatmentRecovery of biogas is not sufficient to produce substantial electricity in case of municipal wastewater

41. UASB: Advantages/DisadvantagesAdvantagesLow energy demandLow land requirementLow sludge productionLess expensive than other anaerobic processesHigh organic removal eficiencyDisadvantagesLong start-up periodRequires sufficient amount of granular seed sludge for faster start-upSignificant wash out of sludge during initial phase of processLower gas yield than other anaerobic processes

42. Pond Treatment ProcessesCommon NameCommentsUseAerobic Stabilization PondsTreatment with aerobic bacteria; oxygen is supplied by algal photosynthesis and natural surface reaeration; depth of 0.15 to 1.5 mCarbonaceous BOD removalMaturation (tertiary) PondsUse aerobic treatment; applied loadings are low to preserve aerobic conditionsSecondary effluent polishing and seasonal nitrificationFacultative PondsTreatment with aerobic, anaerobic and facultative bacteria; the pond has 3 zones: a surface aerobic zone, a bottom anaerobic zone, and an intermediate zone partly aerobic-anaerobicCarbonaceous BOD removalAnaerobic PondsTreatment with anaerobic bacteria; depths of up to 9.1 m to conserve anaerobic conditions Carbonaceous BOD removal (waste stabilization)

43. Land treatment methodsApplication of wastewater on the landPlants and soil play roles in pollutant removalThree types of application:Slow rate infiltrationRapid infiltrationOverland flow

44. Sludge Management Stages and Processes

45. Criteria for WWT Technology Selection

46. WWTT selection criteria used in AA

47. Relative Evaluation of Main Sewage Treatment Technologies

48. Example: Selection of BWWTT by MCA method

49. 4. Treated Wastewater ReuseOverview of Global treated wastewater reuse (GWI 2009)Fit-for-purpose

50. Cases: Wastewater Treatment in AA

51. Kality Stabilization Pond The largest pond (Facultative + Maturation)Treating upto 10 000 m3/d Pond compound area 20 ha New WWTP: 100 000 m3/dUASBExisting pondTFUnrestricted irrigationSludge drying bed

52. Kality Stabilization Pond- PerformanceParameterUnit Influent qualityEffluent quality BOD5mg/L229-32441-55CODmg/L480-697123-142TSSmg/L188-23763-79TNmg/L85-9530-43TPmg/L13-169-12T. ColiformMPN/100ml28-90 billion0.33-0.34 billionSource:(Mengesha, 2011)

53. New Kality Wastewater Treatment PlantInfluentEffluent

54. Mikililand Stabilization Pond Highly concentrated influent due to shortage of water Pond not performing wellOptions for improvement: Upgrade it to aerated pond Use highly active microbes

55. Notes on the operating Wastewater Treatment Plants Bole Homes Aerated PondBuilt long time ago Abundant plant growth No clear plan of improvement

56. THANK YOU !!