Activated sludge process

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<ul><li>1.Activated Sludge Process</li></ul><p>2. Thought of the Day31-May-13 2Activated Sludge Process 3. 31-May-13 3Activated Sludge Process 4. 31-May-13 4Activated Sludge Process 5. Water/Wastewater Termsactivated sludge: sludge particles produced by the growth ofmicroorganisms in aerated tanks as a part of the activated sludge processto treat wastewateraeration: exposing to circulating air; adds oxygen to the wastewater andallows other gases trapped in the wastewater to escape (the first step insecondary treatment via activated sludge process)biochemical oxygen demand (BOD): a laboratory measurement ofwastewater that is one of the main indicators of the quantity of pollutantspresent; a parameter used to measure the amount of oxygen that will beconsumed by microorganisms during the biological reaction of oxygen withorganic materialbiosolids: sludge that is intended for beneficial use. Biosolids must meetcertain government specified criteria depending on its use (e.g., fertilizeror soil amendment)31-May-13 5Activated Sludge Process 6. Water/Wastewater Termsdecomposition: the process of breaking down into constituent parts orelementsdomestic wastewater: wastewater that comes primarily from individuals,and does not generally include industrial or agricultural wastewatereffluent: treated wastewater, flowing from a lagoon, tank, treatmentprocess, or treatment plantgrit chamber: a chamber or tank used in primary treatment wherewastewater slows down and heavy, large solids (grit) settle out and areremovedinfluent: wastewater flowing into a treatment plant31-May-13 6Activated Sludge Process 7. Water/Wastewater Termslagoons (oxidation ponds or stabilization ponds): a wastewater treatment methodthat uses ponds to treat wastewater. Algae grow within the lagoons and utilizesunlight to produce oxygen, which is in turn used by microorganisms in the lagoon tobreak down organic material in the wastewater. Wastewater solids settle in thelagoon, resulting in effluent that is relatively well treated, although it does containalgaemunicipal: of or relating to a municipality (city, town, etc.). Municipal wastewater isprimarily domestic wastewater.primary treatment: the first stage of wastewater treatment that removessettleable or floating solids only; generally removes 40% of the suspended solids and30-40% of the BOD in the wastewatersecondary treatment: a type of wastewater treatment used to convert dissolvedand suspended pollutants into a form that can be removed, producing a relativelyhighly treated effluent. Secondary treatment normally utilizes biological treatmentprocesses (activated sludge, trickling filters, etc.) followed by settling tanks and willremove approximately 85% of the BOD and TSS in wastewater. Secondarytreatment for municipal wastewater is the minimum level of treatment required bythe EPA.31-May-13 7Activated Sludge Process 8. Water/Wastewater Termssedimentation: the process used in both primary and secondarywastewater treatment, that takes place when gravity pulls particles to thebottom of a tank (also called settling).settling tank (sedimentation tank or clarifier): a vessel in which solidssettle out of water by gravity during wastewater or drinking watertreatment processes.sludge: any solid, semisolid, or liquid waste that settles to the bottom ofsedimentation tanks (in wastewater treatment plants or drinking watertreatment plants) or septic tankstertiary treatment: any level of treatment beyond secondary treatment,which could include filtration, nutrient removal (removal of nitrogen andphosphorus) and removal of toxic chemicals or metals; also calledadvanced treatment when nutrient removal is included31-May-13 8Activated Sludge Process 9. Water/Wastewater Termstotal suspended solids (TSS): a laboratory measurement of the quantityof suspended solids present in wastewater that is one of the mainindicators of the quantity of pollutants presenttrickling filter process: a biological treatment process that uses coarsemedia (usually rock or plastic) contained in a tank that serves as a surfaceon which microbiological growth occurs. Wastewater trickles over themedia and microorganisms remove the pollutants (BOD and TSS). Tricklingfilters are followed by settling tanks to remove microorganisms that washoff or pass through the trickling filter media.turbidity: the cloudy or muddy appearance of a naturally clear liquidcaused by the suspension of particulate matterwastewater: water that has been used for domestic or industrial purposes31-May-13 9Activated Sludge Process 10. Activated Sludge ProcessMixed Liquor Suspended SolidsWaste Activated SludgeReturnedActivatedSludge31-May-13 10Activated Sludge Process 11. Activated Sludge ProcessThe most common suspended growthprocess used for municipal wastewatertreatment is the activated sludge process31-May-13 11Activated Sludge Process 12. Activated Sludge PlantActivated sludge plant involves wastewater aeration in the presence ofa microbial suspension solid-liquid separation following aeration discharge of clarified effluent wasting of excess biomass return of remaining biomass to theaeration tank31-May-13 12Activated Sludge Process 13. Activated SludgeActivated Sludge serves two purposes1. Reducing organic matter in wastewater byusing a complex biological community inthe presence of oxygen and convertingthe organic matter to new cellmass, carbon dioxide and energy2. Producing solids capable of bio-flocculating and settling out in theclarifier to produce and effluent low inBiochemical Oxygen Demand (BOD) andTotal Suspended Solids (TSS)31-May-13 13Activated Sludge Process 14. The Process In activated sludge process wastewater containingorganic matter is aerated in an aeration basin inwhich micro-organisms metabolize the suspendedand soluble organic matter. Part of organic matter is synthesized into new cellsand part is oxidized to CO2 and water to deriveenergy. In activated sludge systems the new cells formed inthe reaction are removed from the liquid stream inthe form of a flocculent sludge in settling tanks. A part of this settled biomass, described asactivated sludge is returned to the aeration tankand the remaining forms waste or excess sludge31-May-13 14Activated Sludge Process 15. Activated Sludge ProcessVariablesThe main variables of activated sludgeprocess are the mixing regime loading rate flow scheme31-May-13 15Activated Sludge Process 16. Oxidation and Synthesis31-May-13 16Activated Sludge Process 17. Oxidation and Synthesis31-May-13 17Activated Sludge Process 18. The BOD CurveThe BOD determination involvesthe measurement of thedissolved oxygen used bymicroorganisms in thebiochemical oxidation of organicmatter. The BOD test bottle isincubated for 5 days at 20oC. Atypical BOD curve is shown inFigure. The BOD5 of secondaryeffluents consists of two majorcomponents a carbonaceousdemand resulting from theoxidation of carbon and anitrogenous demand resultingfrom the oxidation of nitrogen.That is,BOD5 = CBOD5 + NBOD531-May-13 18Activated Sludge Process 19. The Growth CurveThe growth curve has five distinct phasesThese are:1. Adaptation (Lag) Phase This portion of thecurve represents the time required for theorganisms to acclimate themselves to theorganic material present in the wastewater.The numbers of bacteria are notincreasing, however, a shift in the populationof the different species of bacteria in thewastewater is occurring so that the bacteriathat can best utilize these organic materialsbecome predominate.2. Log Growth Phase Once the bacteria haveadapted, only the number of organismspresent limit the rate of growth. Becausebacterial cells reproduce by binary fission(i.e., cell division one cell divides andbecomes two, these two divide and becomefour, then eight, sixteen ), this is known aslogarithmic growth. Food is not a limitingfactor for growth in this phase, that is, foreach cell formed enough food is present toallow it to grow and divide.31-May-13 19Activated Sludge Process 20. The Growth Curve3. Declining Growth Phase In thisphase food becomes a limiting factor tothe growth of the bacterial cell massbecause not every bacterium that isformed has the food required to grow.4. Maximum Stationary Phase Herethe available food is just sufficient tokeep the cell mass at a constant levelwith a rate of growth equal to zero.5. Endogenous (Cell Death) Phase When the supply of food becomesinsufficient to maintain the bacterialmass at a constant level, themicroorganisms are forced tometabolize their own protoplasm.31-May-13 20Activated Sludge Process 21. Sludge AgeTherefore, an optimumsludge age existswhich provide anadequate separation ofthe cell mass from theliquid. For a specificsystem the optimumsludge age can bedetermined by plottingthe sludge volume index(SVI) versus the sludgeage31-May-13 21Activated Sludge Process 22. Activated SludgeThe basic activated sludge process hasseveral interrelated components. Thesecomponents are1. aeration tank2. aeration source3. clarifier4. recycle5. waste31-May-13 22Activated Sludge Process 23. Activated SludgeAeration tank. A single tank or multiple tanks designed generally for eithercomplete mix or plug flow with a detention time of as little as 2 hours andup to over 24 hours. The contents of the aeration tank are referred to asmixed liquor.Aeration source. Generally either diffused air or surface mechanicalaeration used to supply oxygen and mix the aeration tank contents.Clarifier. A settling tank where the mixed liquor solids are separated fromthe treated wastewater. Most treatment plants employ several secondaryclarifiers.Recycle. Solids that settle in the clarifier and are returned to the aerationtank.Waste. Excess solids that must be removed from the system.31-May-13 23Activated Sludge Process 24. Activated Sludge Flow Diagram31-May-13 24Activated Sludge Process 25. Activated SludgeA typical activated sludgeplant identifies the threemajor control mechanism forthe activated sludgetreatment process1. aeration rate2. return sludge rate3. waste sludge rateControl of three variables inaddition to providing theproper environment (physical,chemical, biological andnutritional requirements) alllead to good sludge quality31-May-13 25Activated Sludge Process 26. Mixed Liquor Suspended SolidsMLSS The combination of raw sewage and biological mass is commonlyknown as Mixed Liquor. In all activated sludge plants, once the sewage (or industrialwastewater) has received sufficient treatment, excess mixedliquor is discharged into settling tanks and the treatedsupernatant is run off to undergo further treatment beforedischarge. Part of the settled material, the sludge (RAS), is returned tothe head of the aeration system to re-seed the new sewageentering the tank. Mixed Liquor is a mixture of raw or settled wastewater andactivated sludge within an aeration tank in the activated sludgeprocess Mixed Liquor Suspended Solids (MLSS) is the concentration ofsuspended solids in the mixed liquor, usually expressed inmilligrams per litre (mg/l)31-May-13 26Activated Sludge Process 27. Why Measure MLSS If MLSS content is too high The process is prone to bulking and the treatment systembecomes overloaded This can cause the dissolved oxygen content to drop with theeffect that organic matters are not fully degraded andbiological die off Excessive aeration required which wastes electricity If MLSS content is too low The process is not operating efficiently and is wastingenergy Typcial Control band 2,000 to 4,000 mg/l31-May-13 27Activated Sludge Process 28. RAS and WAS A proportion of the floc is called Return Activated Sludge(R.A.S.) and is used to re-seed the process. Measuring the solids concentration of RAS allows the returnvolume to be adjusted to keep the solids level in the aerationbasin within the control parameters Excess sludge which eventually accumulates beyond thatreturned is defined as Surplus or Waste Activated Sludge(SAS/WAS) This is removed from the treatment process to keep the ratioof biomass to food supplied (sewage or wastewater) in balance Typical Range 4,000 to 6,000 mg/l31-May-13 28Activated Sludge Process 29. Activated Sludge ParametersThe parameters in the diagram and a fewothers that will be used for the activatedsludge calculations are summarized in thelist below. primary effluent flow rate, Qo, MGD(m/day for S.I.) primary effluent biochemical oxygendemand (BOD) concentration, So, mg/L(g/m3 for S.I.) primary effluent suspended solidsconc., Xo, mg/L (g/m3 for S.I.) aeration tank volume, V, ft3 (m3 for S.I.) aeration tank MLSS (suspended solidsconc.), X, mg/L (g/m3 for S.I.) secondary effluent flowrate, Qe, MGD, (m3/day for S.I.) secondary effluent susp.solidsconc., Xe, mg/L (g/m3 for S.I.)31-May-13 Activated Sludge Process 29 30. Activated Sludge Parameters secondary effluent biochemical oxygendemand (BOD) concentration, Se, mg/L (g/m3for S.I.) waste activated sludge flow rate, Qw, MGD(m3/day for S.I.) waste activated sludge biochemical oxygendemand (BOD) conc., Sw, mg/L (g/m3 for S.I.) waste activated sludge susp. solids conc., Xwmg/L (g/m3 for S.I.) recycle activated sludge flow rate, Qr, MGD(m3/day for S.I.) Food to Microorganism ratio, F:M, lbBOD/day/lb MLVSS (kg BOD/day/kg MLVSS) Hydraulic retention time, HRT, hours (hoursfor S.I.) Sludge retention time (also called sludgeage), SRT, days (days for S.I.) Volumetric loading, VL, lb BOD/day/1000 ft3(kg BOD/day/m3 for S.I.) % volatile solids in the aeration tank mixedliquor suspended solids, %Vol.31-May-13 Activated Sludge Process 30 31. Activated Sludge Design Parameters31-May-13 Activated Sludge Process 31 32. CalculationsNOTE: F:M values will be the same for units of lb BOD/day/lb MLVSS.Calculations with these design parameters can be made in U.S. units usingthe following equations: V = [ (8.34*So*Qo)/VL ] (1000) VMG = V*7.48/1,000,000 HRT = 24*VMG/Qo F:M = (8.34*So*Qo)/(8.34%Vol*X*VMG)= (So*Qo)/(%Vol*X*VMG)VMG is the tank volume in millions of gallons.It is introduced for convenience in calculations, since the primary effluentflow rate is given in MGD.The 8.34 factor in the equations above is used to convert mg/L to lb/MG,and the 7.48 is for conversion of ft3 to gallons.Also, note that the primary sludge flow rate is typically very small incomparison with the influent wastewater flow rate, so the primary effluentflow rate, Qo, is typically taken to be equal to the plant influent flow rate.31-May-13 Activated Sludge Process 32 33. Example # 131-May-13 Activated Sludge Process 33 34. Example # 231-May-13 Activated Sludge Process 34 35. Calculations in S.I. Units31-May-13 Activated Sludge Process 35 36. Example # 431-May-13 Activated Sludge Process 36 37. Example # 531-May-13 Activated Sludge Process 37 38. Example # 631-May-13 Activated Sludge Process 38 39. Example # 631-May-13 Activated Sludge Process 39 40. Other Aerobic Treatment UnitsStabilization ponds: The stabilization ponds are open flowthrough basins specifically designed and constructed to treatsewage and biodegradable industrial wastes...</p>

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