Modeling Suspended Growth Systems – see Grady, Daigger & LimEnvironmental BiotechnologyCE421/521 Tim Ellis (originally prepared by Dr. Eric Evans)October 25, 2007 Reactor performance as a function of SRT. Fails to account for: Particulate removal rate Anaerobic/anoxic conditions Variable flow and loading Biological nutrient removal1)ˆ()1(−−+=bbkSccsµθθθθθccbSSYX+−=1)(0Monod Equation and Unified ModelInternational Association on Water Quality Activated Sludge Model 1 (IAWQ-ASM 1) In 1983, IAWQ appointed a task group to develop a model. In 1986, ASM 1 was completed. ASM 1 able to predict performance of soluble and particulate substrate removal, nitrification and denitrification under steady state and dynamic conditions.Traditional vs. Lysis-regrowthTraditional vs. Lysis-regrowthASM 1 Tracks 13 individual components through eight separate processes. Assumes heterotrophic growth under anoxic conditions. Limited anaerobic activity. Uses lysis-regrowth approachIAWQ – ASM 2 In 1995, ASM 2 was released capable of tracking biological phosphorus flows. Now able to model enhanced biological phosphorus removal.ASM 2 Tracks 19 separate components through 19 processes. 22 stoichiometric coefficients and 42 kinetic parameters Ammonification and hydrolysis simplified to stoichiometric terms; i.e. rates implicit. Includes anaerobic fermentation, uptake of acetate, formation of PHB and PHAs, and release of soluble phosphate from hydrolysis of polyphosphate. Several assumptions made that constantly need revision as knowledge evolves.Activated Sludge Models Cannot solve analytically. Use computer algorithm based on numerical techniques SSSP, Bidstrup and Grady (MS-DOS based, ASM 1) GPS-X, Hydromantis, Inc. BioWin, EnvironSim Associates Limited. ASIM & AQUASIM, Swiss Federal Institute of Aquatic Science and Technology, EAWAG. EFOR, DHI, Inc. STOAT, WRc Group. WEST, Hemmis N. V. SIMBA, IFAK-System GmbH. ASM 2 integrated into software algorithm provides a powerful tool.Steady-state performance –Particulate versus Soluble Particulate hydrolysis is a rate limiting step. A particulate feed requires a longer SRT to achieve treatment. Particulates compose all of MLSS at low HRTs and active fraction is washed out.Dynamic performance –Particulate and Soluble Flow & substrate concentrations vary during diurnal pattern. Particulate and soluble feeds have different effects on performance.Nitrification – low µmaxand KSDiurnal flow has a negative effect on nitrificationNitrification Nitrifiers are affected by: Temperature Low oxygen concentrations Inhibition by some organicsNitrification Autotrophs are a small fraction of MLSS. Nitrification consumes large amount of oxygen.Denitrification Denitrification – Organics are electron donor Nitrates are electron acceptor Optimum Carbon to Nitrate ratio based on balance between electron donor and acceptor.NitrateCarbonDenitrification Oxygen is preferred electron acceptor…Diurnal flow with different aeration strategies Single CSTR may be set to: Maintain a constant dissolved oxygen concentration in the tank Constant oxygen flow into tankModified Ludzack Ettinger Use an anoxic basin and an aerobic basin to select for denitrification after nitrification… Why denitrify? Where would you place anoxic selector in flow scheme?Effect of SRT on MLE SRT is biomass in system divided by biomass wasted from system where system includes both aerobic and anoxic basins…CSTRMLEDashed lines indicate performance of a single CSTR of the Dashed lines indicate performance of a single CSTR of the same volume as the anoxic and aerobic reactors.same volume as the anoxic and aerobic reactors.MLE Recycle affects performance in MLE Greater recycle leads to: Nitrate flow into anoxic reactor and thus higher consumption of nitrates and organics. Dilution of ammonia in anoxic reactor.ANOXICAEROBICSolid lines indicate the anoxic (first) reactor and the dashed indicate The second (aerobic) reactor.Diurnal Flow Wastewater flow and strength reflect activity of population. Expect diurnal flow pattern.Diurnal Flow Dynamic flow results in lower performance. Performance not solely a function of SRT. Also depends on biomass change as a result of changing input.1)ˆ(θ)θ1(1)ˆ(θ)θ1(dtdXX1cdtdXXθcccc−−−++=−−+=HHHsHHHsbbKSbbKSµµSteady-state equationDynamic equationDiurnal Flow Recall effect of diurnal flow on flow weighted nitrification in CSTR. Must increase SRT to compensate for dynamic condition.Active Populations Heterotrophs Environment=Aerobic Electron Donor Organics Electron Acceptor Oxygen Benefits Removes organics that suffocate or are toxic to the environment Drawbacks Consumes Oxygen (Costs money) Produces large amounts of sludgeActive Populations Heterotrophs Environment=Anoxic Electron Donor Organics Electron Acceptor Nitrates Benefits Removes nitrates Reduces oxygen use Generates alkalinity Drawbacks Anoxic environment may be difficult to createActive Populations Autotrophs Environment =Aerobic Electron Donor Ammonia Electron Acceptor Oxygen Benefits Removes ammonia Drawbacks High oxygen consumption Reduces alkalinityActive Populations Phosphate Accumulating Organisms Environment=Anaerobic/Aerobic Benefits Removes Phosphorus Drawbacks Complex life cycle Requires numerous recycle lines Phosphorus rich sludgeEBPRVirginia Initiative Plant System to remove: Organics Nitrogen Ammonia Nitrates Phosphorus Environments needed: Aerobic Anoxic Anaerobic System configuration?Virginia Initiative Plant System configuration: Anaerobic Anoxic Aerobic Recirculation RAS to Anoxic MLR from Aerobic to RAS MLR from Anoxic to AnaerobicVIPVIP Benefits? Drawbacks?VIPVIP Important consideration: BOD5/Total P ratioVirginia Initiative Plant BOD5/∆P ratio needed for VIP Process? 15-20 mg BOD5/mg