UPPSALA UNIVERSITETAVDELNINGEN F�OR SYSTEMTEKNIKBC, PSA, 9711, last revision O tober 21, 2004 by BC

SIMULATION OF ACTIVATEDSLUDGE PROCESSES WITHNITROGEN REMOVALComputer laboratory work in Wastewater TreatmentPreparation exer ises:1. Read the lab instru tion arefully2. Page 17-18 Exer ise 4.3 a-bName Comments by supervisorProgram Year entering the programDateLab passed Sign

CONTENTS i

Contents1 Introdu tion 12 Simulation of an a tivated sludge pro ess 22.1 Pro ess layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22.1.1 Volumes, ows and omposition of the wastewater . . . . . . . 22.1.2 The sedimentation unit . . . . . . . . . . . . . . . . . . . . . . 32.2 The graphi al user interfa e (GUI) . . . . . . . . . . . . . . . . . . . . 32.3 Running the simulator . . . . . . . . . . . . . . . . . . . . . . . . . . . 52.3.1 Starting the simulator . . . . . . . . . . . . . . . . . . . . . . . 52.3.2 Reseting the simulator . . . . . . . . . . . . . . . . . . . . . . . 52.3.3 Plotting and presenting data . . . . . . . . . . . . . . . . . . . 52.3.4 Changing the pro ess . . . . . . . . . . . . . . . . . . . . . . . 62.3.5 Controlling the pro ess . . . . . . . . . . . . . . . . . . . . . . 63 Exer ises - Pre denitri� ation pro ess 94 Exer ises - Post denitri� ation pro ess 16A Appendix 1 22B Appendix 2 23C Appendix 3 25

1 Introdu tion 11 Introdu tionModeling and simulation studies be ome more and more ommon also in the wastew-ater treatment area. Sin e, a wastewater treatment plant is a very dynami pro ess,stati rules of thumb may not be suÆ ient in the design and operation of the plant.In all simulation studies it is of fundamental importan e to be aware of model ap-proximations and the validly of the model. Note that di�erent needs often lead todi�erent requirement of the a ura y of the underlying model.In this laboratory work, a simulator based on the A tivated Sludge Model No 1(ASM1), will be used to simulate an a tivated sludge pro ess. The simulator is de-noted JASS (a Java based A tivated Sludge pro ess Simulator). The JASS simulatoris written in Java and was made as a master thesis work by P�ar Samuelsson in 1999.It has been updated by Mats Ekman in 2001 and by Gustav Grusell (Master the-sis work in 2002). You will run the simulator using an ordinary web browser (forexample Mozilla, Opera or Explorerr) with Java Plugin installed and enabled. Thepurpose of the laboratory work is to study di�erent aspe ts of nutrient removal inthe a tivated sludge pro ess. Two di�erent alternatives for nitrogen removal in ana tivated sludge pro ess will be onsidered:� Pre denitrifying pro ess� Post denitrifying pro ess

2 Simulation of an a tivated sludge pro ess 22 Simulation of an a tivated sludge pro ess using theASM1 and a graphi al pro ess simulator2.1 Pro ess layoutIn the default version of the simulator program, an a tivated sludge pro ess with predenitri� ation and with the possibility to add an external arbon sour e in ompart-ment 1 is used. It is also possible to hoose the setup for simulating a post denitrifyingpro ess, see Se tion 4. A s hemati layout of the pro ess is shown in Figure 1 (lowerhalf).2.1.1 Volumes, ows and omposition of the wastewaterThe simulated pro ess onsists of a basin divided in 10 ompletely mixed ompart-ments and a sedimentation unit (settler) The (default) on�guration of the ompart-ments is given in Table 1.Compartment No. Volume (m3) Operation1 235 Anoxi 2 235 Anoxi 3 235 Anoxi 4 235 Anoxi 5 235 Anoxi 6 235 Aerobi 7 235 Aerobi 8 235 Aerobi 9 235 Aerobi 10 235 Aerobi Table 1: The basin onsists of 10 ompartments, ompartments 1 to 5 are non-aerobi (anoxi ) and ompartments 6-10 are aerobi .The nominal ow rates used in the simulator are given in Table 2.Flow Rate [m3/h℄In uent 250Ex ess sludge 4Return sludge 250Internal re ir ulation 0External arbon ow rate 0Table 2: Nominal values of the ow rates in the the simulation model.Ea h ompartment is modeled with the ASM1. The values of the parameters and on entrations in the model an be hanged. The default on entrations of di�erent ompounds in the in uent wastewater are given in Table 3.

2.2 The graphi al user interfa e (GUI) 3Standard abbrev. Abbrev. in simulator Variable Con . (mg/l)XB;H Xbh Heterotrophi biomass 0XB;A Xba Autotrophi biomass 0XS Xs Slowly biodegradable substrate 82XI and XP Xi Part. inert org. matter 43XN;D Xnd Part. biodegradable org. nitrogen 5.8SN;H Snh NH4-NH3 nitrogen 23.5SN;D Snd Soluble biodegradable org. nitrogen 2.1SN;O Sno Nitrate and nitrite nitrogen 1SI Si Soluble inert org. matter 37SO So Oxygen 0.1SS Ss Readily biodegradable substrate 80Table 3: In uent wastewater omposition. The values approximately orrespondto the omposition of pre sedimented wastewater at the main muni ipal plant inUppsala.2.1.2 The sedimentation unitThe sedimentation unit is modeled as a traditional one-dimensional layer model with10 verti al layers. The equations des ribing the sedimentation model is given in Ap-pendix 2.The ex ess sludge is removed at the bottom of the sedimentation basin. The sludgeage is al ulated as �s = V �XQw �Xre +Qeff �Xeff [days℄ (1)where V is the volume of the aerobi ompartments, X is the mean sludge on entra-tion in the aeration basin, Qw is the ex ess sludge ow rate (expressed in m3/day),Xre is the on entration of the sedimented sludge, Qeff is the e�uent biomass owrate (expressed in m3/day) and Xeff is the on entration of the e�uent biomass.The sludge age presented in the simulator is al ulated using (1).2.2 The graphi al user interfa e (GUI)The simulator is operated with a GUI where also the status of the plant is shown inreal time. As seen from Figure 1, the plant is s hemati ally drawn in the GUI. Thesimulated ow rates of the pumps are hanged by li king of the appropriate pumpsymbol in the pro ess image, or sele ting the orresponding item in the Flow ratessub-menu, lo ated in the Plant properties menu. This displays a dialog box wherethe ow rate an be hanged.In the upper left orner of the GUI, the simulation time is presented during thesimulation. Note, that some hanges may take hours or days before they are fullyobservable.Important pro ess parameters are also shown in the GUI. For example, in the lowerright of the GUI, the sludge age, the sludge on entration and the ex ess sludge ow

2.2 The graphi al user interfa e (GUI) 4rate are displayed. The sludge on entration is here de�ned as the average on entra-tion of parti ulate ompounds in the aerobi ompartments. To further improve thepresentation of the status of the plant, three bar diagrams are used. Ea h diagramshows the on entration of a sele table ompound in in oming water, all ompart-ments, return sludge and the e�uent water. In these diagrams, the numeri al valuesof the on entrations are also shown. In the GUI an ordinary graph is also used.Here, the on entrations of two ompounds in a spe i� ompartment are plottedversus time.

Figure 1: The graphi al user interfa e in the simulator.

2.3 Running the simulator 52.3 Running the simulatorTo start the simulator (wait until you have started reading Se tion 3 before youa tually do this), do the following:2.3.1 Starting the simulator1. Start a web browser whi h has Java Plugin installed.2. Load the a tual URL, see Se tion 3 for details.3. Sele t the plant to be simulated in the Load plant setup sub menu, lo ated inthe Simulation menu (upper left orner).4. Cli k on the Start button ( ), lo ated just below the menu bar in the GUI.2.3.2 Reseting the simulator5. The simulation an be reseted in two di�erent ways, whi h gives di�erent re-sults:� By reloading the urrent plant setup from the Load plant setup sub-menuin the Simulation menu. In this ase, everything is reseted to initial values,even model parameters.� By pressing the Reset button. This resets the internal states of the om-partments and the sedimentation unit to their initial values. Nothing elseis hanged, so any hanges made to ompartment volumes, ontrollers et remains.2.3.3 Plotting and presenting data6. To hoose a ertain omponent to plot in the bar diagrams, use the ombobox to the left of a bar diagram. For instan e, to plot the on entration ofdissolved oxygen, hoose SO. The oxygen on entrations in in uent water, all ompartments, return sludge and e�uent water are then displayed.7. In the s rolling graph it is possible to plot the on entrations of two omponentsat the same time. Three ombo boxes are lo ated under the graph. In themiddle ombo box it an be hosen whether to plot on entrations from in uentwater, any of the ompartments, return sludge or the e�uent water. Two omponents may then be sele ted from the ombo boxes to the left and to theright.8. The simulated time is presented in the top-left orner of the GUI, below themenu bar, in the �eld labeled Simulation time.9. The sludge age, the ex ess sludge ow and the sludge on entration in the plantare displayed in the lower left of the GUI, in the area labeled Sludge properties.

2.3 Running the simulator 610. The state of the sedimentation unit is shown in the pro ess image. Here the on entration pro�le of parti ulate matter in the sedimentation unit is shown.The darkness of the olor of ea h layer is proportional to the sludge on en-tration. When a sludge over ow o urs, a warning message appears above thesedimentation unit.11. In the se tion labeled Treatment results, lo ated in the lower left of the GUI,the on entrations of COD, BOD, total N, ammonium (Snh), nitrate (Sno) andTotal Suspended Solids (TSS) in in uent and e�uent of the plant are displayed.The redu tion per entage is also shown, see further Appendix 3.2.3.4 Changing the pro ess12. Changes in the pro ess are performed in a number of di�erent dialog boxes.It is important to note that no hanges take e�e t until the Apply or the OKbutton is pressed. The OK button also loses the dialog box. The Can elbutton loses the dialog box without applying any hanges.13. To hange a ow rate, li k on the appropriate pump symbol or sele t theappropriate item in the Flow rates sub-menu, lo ated in the Plant propertiesmenu. Sometimes it may happen that a li k on the pump symbol is notdete ted, then use the sub-menu Flow rates instead. Note also that the dialogbox may hide under the main GUI window.In the dialog box that is displayed, enter the new ow rate (Flow average). Itis also possible to add a sinusoidal variation with a given magnitude and periodtime.An a tive pump will be olored green, and an ina tive yellow. A pump that is urrently being ontrolled by a ontroller will be olored gray. External arbon(ethanol) an be added manually by li king on the pump on the pipe labeledCarbon.14. To hange ASM1 pro ess parameters, sele t ASM1-parameters in the Modelparameters menu. A dialog box where the new parameters may be entered isshown. Here, it is also possible to hoose the simulated temperature of thewater. The ASM1-parameters dialog box is depi ted in Figure 2.15. To hange the on entrations of the omponents in the in uent water, sele tIn uents in the Plant properties menu. A dialog box appears, where new valuesfor the in uent on entrations an be entered.16. By Sele ting Zone volumes in the Plant properties menu, a dialog box appearswhere the volumes of all ompartments an be hanged.17. By sele ting Settler properties in the Plant properties menu, a dialog box ap-pears. In the dialog box it is possible to hange the settler properties su h assettler area, settler height and the settler feed height.2.3.5 Controlling the pro ess18. During simulation, it is possible to hoose between running the simulator with a�xed ex ess sludge ow rate or with a �xed sludge age. In the default setup, the

2.3 Running the simulator 7

Figure 2: The dialog box for hanging the ASM1 pro ess parameters.simulator is running with a �xed ex ess sludge ow rate. By sele ting Ex esssludge ontroller in the Controllers sub-menu, lo ated in the Plant propertiesmenu, a dialog box is displayed where the ontroller for the ex ess sludge ow an be enabled. This is done by he king the Sludgeage ontrol he kbox andthen entering the desired �xed sludge age. The simulator will then run witha �xed sludge age. By he king the Manual ow ontrol he kbox the ex esssludge ow rate will be �xed instead.19. The dissolved oxygen (denoted So in the simulator) is ontrolled by a PID ontroller: u(t) = K(e(t) + 1Ti Z e(t)dt+ Td de(t)dt )where u is the ontrol signal (air ow rate), e is the ontrol error (Soref �So).If Ti = 0 is sele ted, the integration is not used and a pure PD ontroller isobtained. For the oxygen ontrol, no derivative a tion is needed ( Td should be0)To hange the referen e values1 for dissolved oxygen, sele t DO PID ontrollersin the Controllers menu. A dialog box is displayed with 10 tabs labeled zone1,zone2,..., zone10. In ea h of the tabs, parameters for the DO PID ontrollerfor the zone is displayed. Enter the new DO referen e value in the �eld labeled1In the des ription we will use referen e value and set point inter hangeable.

2.3 Running the simulator 8Referen e value. Note that this dialog box works a little di�erent than theothers. Pressing the Apply button applies any hanges done in the urrent tab,while pressing the Reset button resets the urrent tab to the latest appliedvalues. The Can el button loses the dialog box. This makes it ne essary topress Apply every time a hange is made in a ompartment. Also note thatthe air bubbles in the ompartment pi ture in the GUI will disappear whenDOref = 0 is hosen.20. It is also possible to use a supervisory ontroller for the DO ontrollers. Thenthe oxygen ontroller above is used but also a master ontroller for ontrollingthe set point of dissolved oxygen. The goal for the supervisory ontroller isto ontrol the dissolved oxygen levels so that the ammonium level in a desired ompartment (typi ally the last aerated ompartment) is kept at a desired setpoint. The ontroller is given bySoref (t) = K(eA(t) + 1Ti Z eA(t)dt+ Td deA(t)dt )where the ontrol error is given by eA = Snh� Snhref .In order to run the supervisory DO ontroller, sele t DO setpoint ontrollerin the Controllers menu. In the Referen e value �eld, the referen e value forammonium on entration should be entered. In the Referen e zone ombo boxit is also possible to sele t in whi h zone the ammonium on entration shouldbe ontrolled. The user may also set the PID-parameters of the ontroller. Touse the DO setpoint ontroller, the Controller enabled radio button must besele ted.21. It is possible to automati ally ontrol the ow rate of external arbon by thefollowing PID ontroller:ukol(t) = K(ekol(t) + 1Ti Z ekol(t)dt+ Tddekol(t)dt )where ukol is the ontrol signal ( ow rate of arbon), ekol is the ontrol error(Sno-Snoref ). The output Sno is the nitrate level in a sele ted ompartment(by default the last anoxi ompartment)The arbon ontroller is a tivated by sele ting Ext. arbon ontroller in theControllers menu. In the dialog box that is displayed, sele t the ontrollerenabled to enable the ontroller. The ontroller uses the value given in theReferen e value �eld as referen e value for the nitrate on entration in thezone sele ted in the Referen e zone he kbox. It is also possible to set the zonewhere the arbon is added, the PID-parameters and the min and max ow rate.Note that the minimum and maximum values are in m3=h, while in the rest ofthe GUI arbon ow rate is presented in l=h.

3 Exer ises - Pre denitri� ation pro ess 93 Exer ises - Pre denitri� ation pro essYou will here study the e�e t on the pro ess when hanging di�erent pro ess param-eters. Some supporting al ulations will also be done.Exer ise 3.1, Getting used to the simulatorFirst, start a web browser and go to the following URL: www.it.uu.se/resear h/proje t/jass/.Sele t the link JASSeng in the table. Load the predenitri� ation plant by sele tingpre-denit-10 in the Load plant setup sub menu, lo ated in the Simulation menu (upperleft orner).Push the Start ( ) button to start the simulations.Familiarise yourselves with the simulator! Go brie y through the items presented inSe tion 2.2. Reload the simulator if you have made any hanges. Che k that youhave the predenitri� ation plant loaded!Che k that:� The ow of the in oming water=250 m3/h, the internal re ir ulation=0 m3=h,the ex ess sludge ow=4 m3/h and the return sludge ow = 250 m3/h.� The three bar diagrams to the left show readily biodegradable substrate (Ss),ammonium (Snh) and nitrate (Sno)� The oxygen on entrations should be around 2 mg/l in the last �ve ompart-ments and zero in the �rst �ve. This is he ked by hoosing So in one of thebar diagrams.Note that in the lower right of the GUI, in the area labeled Treatment results, you an see some important information about in uent and e�uent on entrations andthe per entage redu tion of di�erent ompounds.Let the simulator rea h steady state values (this may take 5-10 days) and he k:� E�uent ammonium (Snh) = ::::::::::::::::::::::: mg/l� E�uent nitrate (Sno)= ::::::::::::::::::::::: mg/l� Nitrate (Sno) in last anoxi ompartment = ::::::::::::::::::::::: mg/lExer ise 3.2, E�e t of internal re ir ulation rateAn in rease of the internal re ir ulation rate redu es the e�uent nitrate on entra-tion if the denitri� ation is omplete or almost omplete.Assume that the in uent ow is Q, internal re ir ulation is rQ, return sludge is sQ.Assume further that� No other rea tions than denitri� ation and nitri� ation are a�e ting the nitro-gen mass balan e.� Nitri� ation only o urs in aerated ompartments and denitri� ation only o - urs in non aerated ompartments. No rea tions o ur in the settler.� The denitri� ation is omplete (SNO = 0 in the last anoxi ompartment).

3 Exer ises - Pre denitri� ation pro ess 10The following mass balan e then holds:Q SNH;in = (Q+ rQ+ sQ)SNO;eff +Q SNH;eff (2)whi h an be written asSNO;eff = 11 + r + s(SNH;in � SNH;eff ) (3)a) Use (3) to al ulate r so that SNO;eff = 6 mg/l. Assume that SNH;eff is nota�e ted by the re ir ulation rate r and hen e is the same as in Exer ise 3.1. Thein uent ammonium level is SNH;in =23.5 mg/l.'&

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ANSWER:b) In rease the internal re ir ulation rate in the simulator a ording to Exer ises 3.2Fill in the values below.� Internal re ir ulation rate = ::::::::::::::::::::::: m3/h� E�uent ammonium = ::::::::::::::::::::::: mg/l� E�uent nitrate = ::::::::::::::::::::::: mg/l� Nitrate in last anoxi ompartment = ::::::::::::::::::::::: mg/lDid the e�uent nitrate roughly (�10%) be ome as expe ted?'&

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ANSWER: ) Next, in rease the internal re ir ulation rate to 1000 m3=h. Fill in the valuesbelow.� E�uent ammonium = ::::::::::::::::::::::: mg/l� E�uent nitrate = ::::::::::::::::::::::: mg/l� Nitrate in last anoxi ompartment = ::::::::::::::::::::::: mg/lIs expression 3 still valid? If not, try to explain what assumption presented in Exer ise3.2 that is not valid.

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ANSWER:Exer ise 3.3, E�e t of in oming biodegradable substratea) Now, set the internal re ir ulation ba k to zero and hange the on entration ofreadily biodegradable substrate SS in the in uent water to 25 mg/l (Go to Plantproperties/in uent in the menu). Wait for the pro ess to rea h steady state.Note the e�uent levels of ammonium and nitrate.� E�uent ammonium = ::::::::::::::::::::::: mg/l� E�uent nitrate = ::::::::::::::::::::::: mg/lWhat an you say about the ammonium and nitrate levels ompared to the ase inExer ise 3.1?'&

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ANSWER:b) Whi h biologi al pro ess is most sensitive to la k of readily biodegradable sub-strate in the in uent water?'&

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) Now, in rease the internal re ir ulation to the same value as used in Exer ise 3.2b� E�uent nitrate = ::::::::::::::::::::::: mg/l� Nitrate in last anoxi ompartment = ::::::::::::::::::::::: mg/lCompare the result with Exer ise 3.2 b. Is the e�uent nitrate level de reased signif-i antly? Does it seem feasible to in rease the re ir ulation rate in this ase?

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ANSWER:Exer ise 3.4, Adding an external arbon sour eIn this exer ise you should ontinue with the same internal re ir ulation as above.A ommon way of getting a higher denitri� ation rate when there is a la k of eas-ily degradable organi matter in the anoxi ompartments is to add external arbon(ethanol in our ase) in the �rst anoxi ompartment.A arbon sour e is added by li king on the arbon pump and enter a ethanol owrate (l/h) in the dialog box that appears. In the dialog box it is also possible to sele tto whi h zone the arbon is added. By default the �rst anoxi ompartment, zone 1,is sele ted, so leave the zone sele tion un hanged.Try to add a arbon ow rate so that the e�uent nitrate is (approx) 6 mg/l. Fill inthe table below.� External arbon ow rate = ::::::::::::::::::::::: l/h� E�uent ammonium = ::::::::::::::::::::::: mg/l� E�uent nitrate = ::::::::::::::::::::::: mg/l� Nitrate in last anoxi ompartment = ::::::::::::::::::::::: mg/lComment on your results! Compare your results with Exer ise 3.3.'&

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ANSWER:Exer ise 3.5, Changing the DO levelsa) First of all, turn o� the external arbon ow and set the on entration of Ssba k to 80 mg/l. Let the internal re ir ulation ow rate be 250 m3. Wait for thesimulations to rea h steady state. Write down values of air ow rates, ammoniumand nitrate on entrations.� Air ow rates in ompartment 6:::::::::::; 7:::::::::::; 8:::::::::::; 9:::::::::::; 10:::::::::::� E�uent ammonium = ::::::::::::::::::::::: mg/l

3 Exer ises - Pre denitri� ation pro ess 13� E�uent nitrate = ::::::::::::::::::::::: mg/lb) The dissolved oxygen on entration has a large impa t on the a tivated sludge pro- ess. By default, it is set to 2 mg/l in all the �ve aerobi ompartments. Change theDO set-point (the referen e value of dissolved oxygen) to 1.5 mg/l in ompartments6 to 10. In order to do this, go to Plant properties/Controller/DO PID Controllersand sele t set the referen e value to 1.5 for zone 6 to 10. See Se tion 2.3Verify in the bar diagram that all aerobi ompartments have DO=1.5 mg/l. Writedown the values of: air ow rates, nitrate on entrations and e�uent ammoniumafter you have hanged DO set-point.� Air ow rates in ompartment 6:::::::::::; 7:::::::::::; 8:::::::::::; 9:::::::::::; 10:::::::::::� E�uent ammonium = ::::::::::::::::::::::: mg/l� E�uent nitrate = ::::::::::::::::::::::: mg/lCompare the results with 3.5a and omment.'&

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ANSWER:Exer ise 3.6, In rease of in uent ammonium - Optional task.First, hange all �ve ( ompartment 6-10) oxygen referen e values ba k to 2.0 mg/l.Let the simulator rea h steady state values (this may take 5-10 days). Choose So andSnh in ompartment 10 in the time graph. In rease the ammonium on entration by4.5 mg/l (to 28 mg/l) and study the e�e t in ammonium, nitrate on entrations, andair ow rates. Explain what happens with the air onsumption and the ammoniumlevels in the e�uent. Why do the nitrate on entrations in rease? (Compare theresults to Exer ise 3.5).� Air ow rates in ompartment 6:::::::::::; 7:::::::::::; 8:::::::::::; 9:::::::::::; 10:::::::::::� E�uent ammonium = ::::::::::::::::::::::: mg/l� E�uent nitrate = ::::::::::::::::::::::: mg/l'&

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3 Exer ises - Pre denitri� ation pro ess 14Exer ise 3.7, In rease of ex ess sludge owThe amount of biomass in the biorea tor a�e ts the whole pro ess. The most riti alpro ess to maintain is usually the nitri� ation pro ess, why? Change the ex ess sludge ow rate to 40 m3/h and study the ammonium on entration, nitrate on entrationand air ow rates. Explain what you see.'&

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ANSWER:Now you have made a wash-out! Be thankful it was only done in a simulator.Exer ise 3.8, De rease of the temperature - optional taskReload and restart the simulator. Set the internal re ir ulation ow rate to 250m3/h,and wait for the pro ess to rea h steady state. The a tivated sludge pro ess isa�e ted by the temperature, some pro esses more than others. Change the simulatedtemperature to 10 oC. This is done by sele ting ASM1-parameters in the Modelparameters menu and enter the value in the Pro ess temperature �eld in the displayeddialog box. Note how this a�e ts the pro ess parameters. What seem to happenwhen the temperature is de reased? What pro ess is most a�e ted? Motivate thisby he king the pro ess parameters!'&

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ANSWER:As you an see the temperature de rease leads to high ammonium levels in the e�uentwater. A way of dealing with this problem is to aerate more ompartments. Whenmore ompartments are aerated you may not have omplete denitri� ation in the lastanoxi ompartment anymore, and the nitrate removal may therefore be in reasedby adding external arbon to the �rst ompartment. Your task is now to make thenitrogen removal of the plant to work as good as possible. The internal re ir ulationmay not be in reased to more than 300 m3/h. For instan e, aerate ompartment4 and ompartment 5 (i.e set the oxygen referen e values in these ompartmentsto about 2.0 mg/l) and wait for simulations to rea h steady state (note that thistakes quite a while). When you add arbon to the �rst ompartment, try not to addmore than is needed to get an almost omplete denitri� ation in your last anoxi ompartment (a reasonable initial guess may be in the order 1-10 l/h). You an alsotry to use the supervisory DO ontroller. Des ribe and explain your results below.

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4 Exer ises - Post denitri� ation pro ess 164 Exer ises - Post denitri� ation pro essLoad the post-denitri� ation plant by sele ting post-denit-10 in the Load plant setupsub menu, lo ated in the Simulation menu (upper left orner).Start the simulations in the same way as before. The simulator has the same in uent on entrations, pro ess onstants, and volumes as the previous one.Exer ise 4.1, Set-point (supervisory) ontrol of the DOMake the following hanges:� In the bar diagram sele t So, Snh and Sno.� Sele t the sludge age to 10 days (Go to Plant properties/ ontrollers/Ex esssludge ontroller).� Turn on the set-point DO ontroller as des ribed in Point 20 in Se tion 2.3.5.This ontroller ontrols the ammonium level in the last aerated ompartment(zone 5). The ontroller adjust the set-point of the DO ontrollers in the aer-ated ompartments so that the ammonia level in the last aerated zone is equalto the referen e value (set point).Try some di�erent ammonium referen e values (for example 0.5, 1, 2 and 4 mg/l)and explain what happens to� DO on entrations and air ow rates.� The total nitrogen redu tion (The total nitrogen redu tion an be studied inthe area labeled Treatment results).'&

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ANSWER:De rease the sludge age for a given ammonia-set point. Why do the DO on entra-tions hanges?'&

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4 Exer ises - Post denitri� ation pro ess 17Exer ise 4.2, Preparations for external arbon dosingReload the plant setup (See Se . 2.3.2) and then start it and let it rea h steadystate values (this may take 5-10 days) and he k:� E�uent ammonium = ::::::::::::::::::::::: mg/l� E�uent nitrate = ::::::::::::::::::::::: mg/lWhat an you say about the levels of nitrate in the e�uent water ompared to Ex-er ise 3.1. What an you do to improve the nitrate removal?'&

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ANSWER:Exer ise 4.3, Cal ulation of external arbon dosageIn many ases, it is of value to al ulate the (approximate) amount of external arbonneeded. A simpli�ed approa h is to be arried out below.a) Consider a ompletely mixed rea tor whi h is des ribed by the ASM1 using thefollowing assumptions:� The dissolved oxygen So = 0. ( ompletely anoxi )� The hydrolysis pro ess is ignored.� The de ay rate is zero.� Only heterotrophi biomass XB;H is onsidered� An (adapted) external arbon ow rate with COD value S and ow rate u isadded.� The dilution rate is D = Q=V .The model then be omes (make sure you an derive this model from the ASM1 matrixand basi biorea tor modeling):dXB;Hdt = �(�)XB;H +D(XB;H;in �XB;H) (4)dSSdt = � 1YH �(�)XB;H +D(SS;in � SS) + SCV u (5)dSNOdt = �1� YH2:86YH �(�)XB;H +D(SNO;in � SNO) (6)where �(�) is the spe i� growth rate whi h depends on several variables (denoted �).

4 Exer ises - Post denitri� ation pro ess 18Consider (4) - (6) during steady state. Derive an expression for the ne essary station-ary ow rate of external arbon u using the following steps. First, assume SS;in = 0(i.e. no internal organi matter available for denitri� ation) and SS = 0 (all external arbon is used). Solve for u in (5). You will note that u depends on 1YH �(�)XB;H .An expression for this an be obtained from (6) and inserted into the expression foru. Finally, let �SNO = SNO;in� SNO and you should end up with a neat expressionfor how mu h arbon ow rate that is needed in order to remove �SNO mg/l nitrate.'&

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ANSWER:

b) Cal ulate the desired ow rate of external arbon (transformed to l/h) for the aseYH = 0:67Q = 250 + 250 = 500 m3/hSC = 1200000 mg/l�SNO = 2 mg/l'&

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Exer ise 4.4, Adding an external arbon sour eMake the following hanges:� Sele t the sludge age to 8 days (Go to Plant properties/ ontrollers/Ex ess sludge ontroller). This is done so that wash-out is not obtained when de reasing theaeration volume in the step below.� Set the dissolved oxygen to zero in ompartment no 5 (Go to Plant proper-ties/ ontrollers/DO PID ontrollers hange the referen e value to 0 for zone5). This done in order to redu e the oxygen in ow to zone 6.� Set Kh = 0 (we assumed no hydrolysis), this parameter an be hanged afteropening the Model parameters/ASM1-parameters dialog box.� Set rh = 5:76 �10�5. This is the hindered zone settling parameter for the settlerunit. The parameter an be hanged after opening theModel parameters/Settlermodel parameters dialog box. This hange is done in order to avoid sludgeover ow in the settler.

4 Exer ises - Post denitri� ation pro ess 19External arbon (ethanol) will be added in order to improve the denitri� ation andredu e the nitrate level in the anoxi ompartments. The ethanol will be added in ompartment 6 (�rst anoxi ompartment). To add ethanol, just li k on the pumpsymbol above the ompartment and enter a value of the ow rate (unit l/h).Set the ow rate as al ulated in Exer ise 4.3b Let the pro ess, rea h steady stateand he k the nitrate removal2 �SNO = Szone5NO � Szone10NO . Write down the nitrateremoval.'&

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ANSWER:Exer ise 4.5, E�e t of hydrolysisSet Kh = 0:125 and ontinue to add external arbon. Now, the nitrate removalshould in rease. Try to explain why.'&

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ANSWER:In the long run, manual ontrol of the external arbon sour e is not a very ost eÆ ientway of getting a good nitrate removal In the next two tasks you will run an automati arbon ow rate ontroller. The key idea of the ontrol strategy3 is to adjust the ow rate so that the nitrate level in the last anoxi zone is kept at a sele ted set-point.Exer ise 4.6, Automati ontrol of the external arbon sour eThe purpose with this exer ise is to illustrate a ontrol strategy for ontrolling theethanol ow rate.First reload the plant setup (See Se . 2.3.2) and start the simulation.Sele t Ext. arbon ontroller in the Controllers menu. The ontroller is startedby sele ting the Controller enabled radio button and pressing Apply. The arbon ontroller is by default setup to ontrol the nitrate on entration in zone 10 by adding2Note that sin e we have a re y le of nitrate we an not state that the nitrate level in the e�uentis de reased with 2 mg/l, what we may say is that the redu tion in the anoxi ompartments shouldbe 2 mg/l.3In the ourse \Modellering o h styrning av milj�otekniska pro esser", period 43 you will learnhow to design and tune a arbon ontroller

4 Exer ises - Post denitri� ation pro ess 20external arbon (ethanol) to zone 6. Do not hange this. A referen e value for thenitrate on entration an be given in the Referen e value �eld. Do not forget to pressapply to make any hanges take e�e t. The ontroller may be turned o� by sele tingthe Controller disabled radio button ( and pressing Apply ), whi h allows for manual ontrol of the arbon ow rate.Try di�erent referen e values (set-points) for the nitrate level and study how the owrate of external arbon is a�e ted.'&

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ANSWER:Exer ise 4.7, Control of the external arbon when in uent ammonium on entration is hangedSet the nitrate level set-point in ompartment 10 to 6.0 mg/l.When the system has rea hed steady state, in rease the on entration of in uentammonium to 40 mg/l. Study how the e�uent nitrate is a�e ted. Can you see anydi�eren es in the nitrate levels when the disturban e is applied?Write down the steady state on entration of the e�uent nitrate when the in uentammonium is 40 mg/l:� E�uent nitrate = ::::::::::::::::::::::: mg/lDe rease the in uent ammonium to 23 mg/l and wait for steady state. Swit h the arbon ontroller to manual mode and then in rease the in uent ammonium to 40mg/l. What happens?� E�uent nitrate = ::::::::::::::::::::::: mg/lSummarize and omment on the result below.'&

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ANSWER:Exer ise 4.8, Sludge over ow in the sedimentation unita) Reload the simulator. Before you push the start button, double both the in uent ow rate and the return sludge ow rate to 500 m3/h ea h, also in rease the in uent on entration of Xi to 300 mg/l. This an be regarded as a storm with sewer ush-out simulation. Start the simulation and look at the state of the sedimentation unit

4 Exer ises - Post denitri� ation pro ess 21in the pro ess image. Note that the height of the sludge blanket is in reasing (thelayers with bla k olor). How long time did it take until you rea hed sludge over ow(40 mg/l suspended solids on entration i e�uent water)?'&

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ANSWER:b) A ording to the solid ux theory, what is the ondition for a sludge es ape in asettler?'&

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ANSWER:

A Appendix 1 22A Appendix 1Constants in modeldeltaT = 0.0100alfa = 5.000000KCs = 8.6370000--- *** ASM1 onstants--- stoi hiometri onstants :Yh = 0.6700Ya = 0.2400fp = 0.0800Ixb = 0.0860Ixp = 0.0600--- kineti onstants for heterotrophi ba teria:mytH = 0.25bh = 0.026Ks = 20.000Koh = 0.2000Kno = 0.5000etaG = 0.8000--- kineti onstants for autotrophi ba teria:mytA = 0.0330ba = 0.0083Knh = 1.0000Koa = 0.4000Ka = 0.00330--- kineti onstants for hydrolysis:Kh = 0.125Kx = 0.0300etaH = 0.4000

B Appendix 2 23B Appendix 2Se ondary settler� Geometry:A: Area = 500 m2zm = 1 to 10: Height of layer m (all equal)Height = 4 mSettler volume = 2000 m3� Solid ux due to gravity sedimentation Js:Js = �s(X)Xwhere X is the total sludge on entration� Double-exponential settling velo ity fun tion:max h0;minn�00; �0 �e�rh(X�Xmin) � e�rp(X�Xmin)�oiXmin = fnsXfMaximum settling velo ity �00 m/h 8.7Maximum Vesilind settling velo ity �0 m/h 18Hindered zone settling parameter rh m3=gSS 0.00057Flo ulant zone settling parameter rp m3=gSS 0.00286Maximum settling velo ity fns 0.00128� Mass balan es for the sludge:{ For the feed layer:dXmdt = QfXfA +J lar;m+1�(�up+�dn)Xm�min(Js;m;Js;m�1)zmwhere Qf is the owrate from the last biorea tor and Xf is the sludge on entration from the last biorea tor.{ For the intermediate layers below the feed layer:dXmdt = �dn(Xm+1�Xm)+min(Js;m;Js;m+1)�min(Js;m;Js;m�1)zm{ For the bottom layer:dX1dt = �dn(X2�X1)+min(Js;2;Js;1)z1{ For the intermediate lari� ation layers above the feed layer:dXmdt = �up(Xm�1�Xm)+J lar;m+1�J lar;mzm

B Appendix 2 24where J lar;j = ( min(�s;jXj ; �s;j�1Xj�1)�s;jXjifXj�1 � Xt{ For the top layer:dX10dt = �up(X9�X10)�(J lar;10z1with J lar;10 = ( min(�s;10X10; �s;9X9)�s;10X10ifX9 � XtThe threshold on entration Xt is equal to 3000 mg/l� For the soluble omponents:{ For the feed layer:dZmdt = QfZfA �(�up+�dn)Zmzm{ For the intermediate layers below the feed layer:dZmdt = �dn(Zm+1�Zm)zm{ For the feed layer and the layers above the feed layer:dZmdt = �up(Zm�1�Zm)zmwhere�dn = Qr+QwA�up = QeffA

C Appendix 3 25C Appendix 3Quality parameters in e�uentThe total suspended solids is al ulated asTSS = 0:75(Xseff +Xieff +Xpeff +Xbheff +Xbaeff ).The total nitrogen on entration is al ulated astotalN = Snoeff + SNKj;effwhereSNKj;eff = Snheff+Sndeff+Xndeff+Ixb(Xbheff+Xbaeff )+Ixp(Xieff+Xpeff ).Bio hemi al oxygen demand is al ulated asBOD = 0:25(Sseff +Xseff + (1� fp)((Xbheff +Xbaeff )and hemi al oxygen demand asCOD = Sseff + Sieff +Xseff +Xieff +Xpeff +Xbheff +Xbaeff .