1 2004 Biological Wastewater Treatment Operators School Advanced Treatment SystemsMay 13, 2004Dean Pond, Black & Veatch
2 Advanced Treatment Systems What are the forms of nitrogen found in wastewater?
3 What are the forms of nitrogen found in wastewater? TKN = 40% Organic % Free AmmoniaTypical concentrations:Ammonia-N = mg/LOrganic N = 10 – 35 mg/LNo nitrites or nitratesForms of nitrogen:Organic NAmmoniaNitriteNitrateTKNTotalN
4 Advanced Treatment Systems Why is it necessary to treat the forms of nitrogen?
5 Why is it necessary to treat the forms of nitrogen? Improve receiving stream qualityIncrease chlorination efficiencyMinimize pH changes in plantIncrease suitability for reusePrevent NH4 toxicityProtect groundwater from nitrate contamination
6 Advanced Treatment Systems What are the effects of N and P in receiving waters?
7 What are the effects of N and P in receiving waters? Increases aquatic growth (algae)Increases DO depletionCauses NH4 toxicityCauses pH changes
8 Advanced Treatment Systems Why is it sometimes necessary to remove P from municipal wastewater treatment plants?
9 Why is it sometimes necessary to remove P from municipal WWTPs? Reduce phosphorus, which is a key limiting nutrient in the environmentImprove receiving water quality by:Reducing aquatic plant growth and DO depletionPreventing aquatic organism killReduce taste and odor problems in downstream drinking water supplies
10 Advanced Treatment Systems How is P removed by conventional secondary (biological) wastewater treatment plants?
11 How is P removed by conventional secondary (biological) WWTPs? Biological assimilationBUG = C60H86O23N12P0.03 lb P/lb of bug massGROW BUGS, WASTE BUGS = REMOVE P
12 Advanced Treatment Systems Where in the treatment plant process flow could chemical precipitants be added?
13 Where in the treatment plant flow could chemical precipitants be added? At pretreatmentBefore primary clarifiersAfter aeration basinsAt final clarifiersAhead of effluent filtersConsiderations:Effective mixingFlexibilitySludge production
14 Advanced Treatment Systems How is N removed or altered by conventional secondary (biological) treatment?
15 How is N removed or altered by secondary (biological) treatment? Biological assimilationBUG = C60H86O23N12P0.13 lb N/lb of bug massBiological conversion by nitrification and denitrification
16 Nitrification NH4+ Nitrosomonas NO2- NO2- Nitrobacter NO3- Notes:Aerobic processControl by SRT (4 + days)Uses oxygen 1 mg of NH4+ uses 4.6 mg O2Depletes alkalinity mg NH4+ consumes 7.14 mg alkalinityLow oxygen and temperature = difficult to operate
17 DenitrificationNO3- denitrifiers (facultative bacteria) N2 gas + CO2 gasNotes:Anoxic processControl by volume and oxic MLSS recycle to anoxic zoneN used as O2 source = 1 mg NO3- yields 2.85 mg O2 equivalentAdds alkalinity 1 mg NO3- restores 3.57 mg alkalinityHigh BOD and NO3- load and low temperature = difficult to operate
18 Advanced Treatment Systems What are typical flow application rates in tertiary filters?
19 What are typical flow application rates in tertiary filters? Automatic backwash filters (1-2 ft media depth) = 2 to 4 gpm/sfDeep bed filters (4-6 ft media depth) = 4 to 8 gpm/sf
20 Advanced Treatment Systems What are typical backwash rates for a tertiary filter (in gpm/sf)?
21 What are typical backwash rates for a tertiary filter (in gpm/sf)? Automatic backwash filters20 to 25 gpm/sf5 to 10% of throughputDeep bed filters15 to 20 gpm/sf3 to 5% of throughput
22 Advanced Treatment Systems Define advanced treatment…
23 Define advanced treatment … Treatment that improves or enhances secondary treatment processesFurther removal of organics, nutrients and dissolved solids
24 Advanced Treatment Systems Explain circumstances under which advanced treatment may be necessary…
25 Explain circumstances under which advanced treatment may be necessary… Limited assimilative capacity of streamToxicity reduction / eliminationNutrient controlClosed systemsWater reuse
26 Advanced Treatment Systems Identify and explain the objectives of the following advanced treatment systems:Further removal of organicsFurther removal of suspended solidsNutrient removal (N and P)Removal of dissolved solids
27 Identify and explain the objectives of the following advanced treatment systems: Further removal of organicsReduce effluent BOD to reduce receiving stream DO depletionImprove disinfectionReduce effluent N to improve water qualityFurther removal of suspended solidsRemoving TSS removes BODRemoving TSS removes N and P (BUG = C60H86O23N12P)Protects stream sediment oxygen demandImproves efficiency of disinfection
28 Removal of nutrients (N and P) Identify and explain the objectives of the following advanced treatment systems:Removal of nutrients (N and P)Reduce oxygen demand of receiving streamControl nutrients and algaeControl taste and odor in downstream drinking waterSuitability for reuse (examples: boiler water recycle, irrigation – N&P control of runoff, groundwater recharge)
29 Removal of dissolved solids Identify and explain the objectives of the following advanced treatment systems:Removal of dissolved solidsRemoval of specific pollutant – zinc, chromium, leadPretreatment of industrial wasteControl effluent toxicityMake suitable for reuse
30 Advanced wastewater treatment… Describe the purpose or procedure and mechanism by which it is done for each of the following:Activated carbon adsorptionChemical coagulationFlocculationPhosphorus removalNitrogen removalEffluent FiltrationPolishing lagoonsNitrificationDenitrificationAmmonia stripingAlum or ion precipitationLime precipitationReverse osmosis (RO)Electrodialysis
31 Activated Carbon Adsorption PurposeTertiary treatmentRemoval of low concentration organic compoundsApplication:Influent Primary Trt Biological Trt Filtration Carbon DisinfectionMany variations
32 Activated Carbon Adsorption Continued …Carbon Regeneration5 to 10% lossLess capacity than new carbonHot 350oFChemicals (sodium hydroxide)Fire / ExplosionCarbon usually replaced after 5 regenerationsMechanism:Active sites “Activated Carbon”Molecular bondingParticles adhere to surface
33 Chemical Coagulation Purpose Application Chemical feed with rapid mix Enhanced removal of organics and fine particlesAddition of lime, alum, iron, polymer to change ionic chargeApplicationChemical feed with rapid mixAhead of final clarifiersAhead of filtration
34 Chemical Coagulation Lime+ Heavy metals Alum+ SS removal Continued …Lime+ Heavy metals Alum+ SS removalSS removal P removalP removalPolymer + - SS control Iron+ SS removalMechanism:Destabilization by ionic charge neutralizationReduce charge that keeps small particles apartAluminum sulfateFerric chlorideFerric sulfateFerrous sulfate____++_++___++_++++__+__+++_++_++++++__+__+__++++__+_____+_++++++
35 Flocculation Purpose Application Produce larger, more dense floc particles that will settle or filter easilyApplicationGentle mixing after rapid mix (coagulation)Mixing – Mechanical or AerationQInfl QGentleMix /FlocculationRapidMix /CoagulationSludge
36 Flocculation Mechanism Continued …MechanismCoagulated particles strung together into larger floc particles (snow flake floc)+
37 Phosphorus Removal Purpose Application / Mechanism Reduce effluent P Biological or chemical methodReduce nutrient load on streamReduce algae growthReduce oxygen depletionApplication / MechanismBiologicalChemical
38 Phosphorus Removal Biological Continued … RAS WAS P Release FinalClarifierRASWASEfflQP ReleaseAnaerobicZoneAerobicP Luxury UptakeP Removal
39 Phosphorus Removal Chemical Continued … Chemical Coagulant Chemical PrimaryClarifierAerobicZoneEfflFinalClarifierQChemicalCoagulantChemicalCoagulantRASWASP Removal
40 Nitrogen Removal Purpose Application / Mechanism Reduce effluent N (ammonia and nitrates)Biological or chemicalReduce nutrient load on streamReduce algae growthReduce oxygen depletionApplication / MechanismAdvanced Activated Sludge ProcessesNitrification (remove ammonia)NH4 NO2 NO3
41 Nitrogen Removal Deep Bed Filtration Air Stripping Continued … Denitrification (remove nitrate)NO3 NO2 NO, N2O or N2 gasDeep Bed FiltrationAnaerobic fixed film bacteria (denitrify)Air StrippingRemoves ammoniaElevated pH to NH4 as gasQMedia6-8’Methanol(carbon)Q
42 Effluent Filtration Purpose Application Remove SS (usually after FC) Reduce BOD and insoluble PApplicationDeep Bed4-6’ sand and gravelLarge cells 10’ x 30’Similar to WTP(batch backwash)hL = ft$$$2. Traveling Bridge1-2’ sand and anthraciteSmall cells 1’ x 14’Contiuous backwashhL = ft
43 Effluent Filtration Loading Rate Mechanism Backwash Continued …Loading RateBackwash2 – 4 gpm/sfFrequency depends on loading20 – 25 gpm/sf5 – 15% of throughputMust clean bedsAir scourMechanismFiltration by granular media
44 Polishing Lagoons Purpose Application To further treat or polish the effluentAfter final clarifierFacultative pond (aerobic and anaerobic)ApplicationTypical volume = 1 day average flowi.e., 1 mgd plant = 1 mgd lagoon24 hour detention timeSurface aerators
45 Polishing Lagoons Mechanism Continued …SunlightSurfaceAeratorAlgaeMSettlingAerobicAnaerobicSunlight Photosynthesis Algae + Organics & NutrientsOrganic Matter Anaerobic DecompositionMechanismAlgae and bacteria grow in pond consuming organics and nutrients in FC effluent. Algae settles and degrades by anaerobic process.methanegas
46 Nitrification Purpose Application Mechanism Reduce ammonia on plant effluentHigh ammonia concentrations are toxic to streamsQuickest impact on DO versus nitratesApplicationSRT > 3 days in activated sludge processGrow Nitrosomonas and NitrobacterNH4 NO2 NO3MechanismBiological conversion of ammonia to nitrate
47 Denitrification Purpose Application Mechanism Reduce nitrate on plant effluentUsually in combination with nitrification to reduce Total N to the streamApplicationActivated Sludge ProcessDeep BedFiltersMechanismBiological conversion of nitrate to N2 gasQAnxOxicFCOxic RecycleRASWAS
48 Ammonia Stripping Purpose Application / Mechanism Reduce ammonia either before or after biological treatmentNot commonly used in the USApplication / MechanismRaise pH 10.8 to 11.5, usually by adding limeMove equilibrium point to ammonia 250C and pH 11NH4 gas = 98%
49 Ammonia StrippingContinued …Break wastewater into droplets and strip off ammonia gas with airFreefall through tower that circulates a lot of air to remove ammonia to atmosphereNH4AirLimeQNH4StripperFlocPrecip.Lime SludgeAirQ
50 Alum or Iron Precipitation PurposeTo remove orthophosphateApplicationAs a backup to Bio-P processAs chemical P removalAs chemical processMechanismAl+ or Fe+ + PO4 Aluminum or Iron PhosphateAl+ or Fe+QFiltrationOptionalQPrecipitateRapidMixRASWAS + Precipitate
51 Lime Precipitation Purpose Application Mechanism P removal before primary clarifier or following biological treatmentApplicationAs a backup to Bio-P processAs chemical P removalAs chemical processHigh pH can be a problem in effluent or in biological treatmentMechanismChemical conversion of phosphorus to calcium phosphate is in pH range of 9.5 to 11.0
52 Reverse Osmosis (RO) Purpose Application Mechanism High quality removal of various salts – calcium, sodium, magnesiumApplicationWater reuseAWTMechanismChemical separation / filtration across a semi-permeable membraneHigh pressureTertiary processUsed in Gulf War to treat sea water sodium removal
53 Electrodialysis Purpose Application Mechanism Removal of ionic inorganic compoundsApplicationAWTMedicalWTPClinicalMechanismApply electrical current between two electrodesWater passes through semi-permeable membranes (ion-selective)Alternate spacing of cation and anion permeable membranesCells of concentrated and diluted salts are formed
54 Electrodialysis Purpose Application Mechanism Removal of ionic inorganic compoundsApplicationAWTMedicalWTPClinicalMechanismApply electrical current between two electrodesWater passes through semi-permeable membranes (ion-selective)Alternate spacing of cation and anion permeable membranesCells of concentrated and diluted salts are formedSludge – concentrated salt waste stream as process reject waterProblems – plugging, fowling of membranes, MUST pretreat activated carbon, multi-media filtration_+H20Cl-H+_+OH-Na+Bipolar Membranes
55 Advanced wastewater treatment… What would be the effect on sludge production for each of the following advanced treatment processes?Activated carbon adsorptionChemical coagulationFlocculationPhosphorus removalNitrogen removalEffluent FiltrationPolishing lagoonsNitrificationDenitrificationAmmonia stripingAlum or ion precipitationLime precipitationReverse osmosis (RO)Electrodialysis
56 TANSTAAFL (tanstaffull) What would be the effect on sludge production for each of the advanced treatment processes?TANSTAAFL (tanstaffull)“There ain’t no such thing as a free lunch.”REMOVE MORE STUFF = GET MORE SLUDGEMore BOD & TSS Removal MORE SLUDGEAdd chemicals MORE SLUDGEN & P Removal MORE SLUDGESome processes produce more sludge than others:Electro/mechanical – some sludgeBiological – more sludgeChemical – MOST sludge