LABORATORY EXERCISE #6 Aerobic Biological Treatability Study ...

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LABORATORY EXERCISE #6 Aerobic Biological Treatability Study ...

1LABORATORY EXERCISE #6Aerobic Biological Treatability Study of Sodium Acetate:Completely Mixed ReactorBefore Lab Questions:These questions must be turned in (individually) on the day the lab is conducted.1) Question #1: Why will you freeze your COD samples?2) Question #2: How will you collect the sample to conduct the COD measurement ofyour reactor effluent?3) Question #3: What will be done to acclimate the bacteria to the substrate before theexperiment is conducted?PurposeTo develop a model for the biodegradation of sodium acetate in an aerobic, completelymixed reactor. The model developed here cannot be used to model the degradation ofphenol in the groundwater system, since phenol and sodium acetate are different organiccompounds. However, the procedure of developing a model for the degradation ofsodium acetate in a pilot scale device (in the lab) that is then applied to a prototype (fieldscalesystem) is the same procedure we will follow to design a system to degrade phenol.TheoryThe principles used in this laboratory exercise to describe the degradation of sodiumacetate will be covered in the course lectures. Details and equations can be found in yourlecture notes.Apparatus• Reactor vessel• Influent reservoir• High-capacity scale• 500 ml and 1l volumetric flasks• Peristaltic pump and associated tubing• Feed solution: 360 mg/l sodium acetate, 130 mg/l (NH 4 ) 2 SO 4 , 4.8 mg/l KH 2 PO 4 , 12.4mg/l K 2 HPO4, 25.5 mg/l Na 2 HPO 4, and 360 mg/l yeast extract. The primarysubstrate is sodium acetate.• Stopwatch and 50-ml graduated cylinder• 10-ml and 25-ml pipettes• Sample collection vials, 8ml capacity• Air stones and associated tubing• Rubber stopper and tubing to pre-saturate air with water vapor• Cuvettes, reagents, and spectrophotometer for making COD measurements• Filter paper and associated assembly for TSS measurementscstr_reactor_08


Reservoir filledwith nutrients andsubstrateFlask to presaturateair with water vaporPeristaltic pump2Air line attached toair stone in reactorCompletely MixedReactorAttach tubing here tocarry effluent to drain.Effluent samples arecollected from this line.Air line attachedto air stone inreactorProcedure1. Make sure that the baffle that was inserted in the reactor for the tracer test is in placeand leaves ~ 1 cm gap between the baffle and the reactor bottom. The reactor shouldbe angled so biomass settles in the settling chamber and flows by gravity into themain reactor chamber.2. A carboy will be used to supply feed solution. Each reservoir will be filled with 18 lof substrate solution (Composition is given above). The TA will prepare thereservoir and feed solution. Your reservoir will be rinsed and filled with freshsubstrate every 72 hours (performed by TA); otherwise, you may find bacteriagrowing in your reservoir.3. Attach tubing from the reservoir spigot to your pump. Adjust the settings on thepump to the desired flow rate for your group, shown in the Table 1. Dump allsubstrate collected for flow adjustment and measurement back into carboy.Table 1. Experimental ConditionsGroupMean HydraulicDetention Time(h)Mean CellDetention Time(days)FlowRate(ml/min)1 18 5 3.52 18 10 3.53 18 15 3.54 18 20 3.55 18 30 3.56 18 (undetermined –no wasting ofreactor solution5. Start the pump and use a 50-ml graduated cylinder to record the volume of watercollected in 8 minutes, approximately. Adjust the collection time so that you arereading to a specific mark on the graduated cylinder. Make this measurement twice.6. Stop your pump and close the spigot from the reservoir.7. Fill the completely mixed reactor with a 2 l solution of water, substrate, nutrients, andactivated sludge. The activated sludge has been “feeding” on the substrate for a3.5cstr_reactor_08


3couple of days and should be acclimated to this feed solution. The TA will prepare a2 l solution for each group before class. The activated sludge was taken from theWilmington Wastewater Treatment Plant.8. Add deionized to the reactor until the water level is at the midpoint of the opening onthe side of the reactor. Tap water must NOT be used, since it contains chlorine thatmay kill bacteria in your reactor.9. Attach tubing from the laboratory airline to a 500 ml flask to pre-saturate the air withwater and then to an air stone in the 500 ml flask. Fill the 500 ml flask with ~ 350 mlof deionized water. Do not use tap water, because chlorine in the gas phase may bestripped from the tap water and enter your reactor. Place the air stone in your reactorusing a pipe fitting to “weigh” down the tubing so it is at the bottom of the reactor.Turn on the air and adjust the airflow rate to create well-mixed conditions within thereactor. The air serves to mix the reactor contents and to supply oxygen to theactivated sludge.10. Attach tubing to the effluent fitting from the reactor such that waste from the reactordrains into a nearby sink.11. Place the end of the pump tubing into the reactor. Secure the tubing to the reactor byclamping it in place. The tubing should NOT be submerged in the water, but shoulddrip into the reactor.12. Open the spigot from the reservoir and “start” your reactor by turning on the pump.Record the time. Collect two 6-7ml samples of water from the influent ( So) using thesample vials. Make sure that there is enough headspace at the top of the vials for thewater to expand when it freezes. Label these samples using tape and a marker,clearly indicating the group number and sample number. Place these samples in thefreezer. The TA will perform COD tests on these samples later. The samples arefrozen so that bacterial activity is hindered between the time the samples are collectedand the time that COD is measured. Record all measurements in lab notebook.13. Cover the reactor with plastic to inhibit evaporative losses.{The reactors must be operated for about one week from the start of the experiment andwill be dissembled on the following lab period.}14. Collect two 10 ml samples from the main section of the reactor (side containing airstone), perform a total suspended solids (TSS) test on the samples, AND measure theCOD of the filtered samples ( S e ). Analyses of TSS will NOT follow procedures inExercise #5, which were approximate. Traditional procedures for measuring TSSwill be followed and are discussed below. In your analyses, we will assume thatVSS = 0.8 TSS.Store the COD samples in the sample vials, labeling them as described above. Placethese samples in the freezer. The TA will perform COD tests on these samples later.15. Collect two 10ml samples from the effluent to the reactor and measure the TSS ofeach sample following the procedures discussed below. Effluent samples should betaken directly from the reactor section where bacteria settle out – not theeffluent tubing.cstr_reactor_08


416. On Saturday and Tuesday, the TA will do the following:• Stop the pump injecting substrate into your reactor.• Rinse out the influent reservoir with chlorine-free deionized water and refill itwith 18 l of the substrate solution.• Restart the pump and flow of substrate into your reactor.17. On EVERY day thereafter until Wednesday (day of disassembly), one person fromeach group must come to the lab to collect COD and TSS samples, waste fluid fromyour reactors to maintain the desired mean cell retention time, and adjust the pumpflow rate as required.• Collect two 10ml samples from the main section of the reactor (containing airstone) and perform a TSS measurement on each.• Collect two 10ml samples from the reactor effluent and perform a TSSmeasurement.• Collect two 6-7ml samples from the influent using the sample vials and placethese samples in the freezer. Make sure that there is enough headspace at thetop of the vials for the water to expand when it freezes.• Collect two 6-7 ml samples from the filtrate collected for the TSSmeasurements. These influent and filtrate samples will be used for CODmeasurements.• Measure the flow rate coming from your substrate reservoir as described instep 5. Adjust your pump settings to maintain desired flow rate (Table 1.)• Calculate the TSS of the samples collected the PREVIOUS sampling period.Using these TSS measurements and the flow rate through your reactor,calculate the volume of solution that must be removed from the main sectionof the reactor (containing air stone) to maintain the mean cell retention time inTable 1. Using appropriate pipettes emove this volume from the reactor,dispose in the sink, and record the volume removed.• TA will take photographs of each reactor.TSS Measurements1. Preparation of glass-fiber filter disk. The TA will perform steps a) through d) beforethe lab. The only thing you must do is weigh the filter paper and planchet, item e).a) Insert disk with wrinkled side up in filtration apparatus.b) Apply vacuum and wash disk with three successive 20-mL portions of distilledwater. Continue suction to remove all traces of water and discard washings.c) Remove filter from filtration apparatus and transfer to aluminum planchet.d) Dry in an oven at 102 to 105 o C for 1 hr.e) Cool in desiccator to balance temperature and weigh. This is the weight of thefilter paper and planchet without any solids.2. Sample analysis for total suspended solids:a) Assemble filtering apparatus and filter and begin suction.b) Wet filter with a small volume of distilled water to seat it.c) Pipette 10-mL volume sample from your reactor onto the seated glass-fiber filter.d) Wash with three successive 10-mL volumes of distilled water, allowing completedrainage between washing and continue suction for about 2 min after filtration iscomplete.cstr_reactor_08


5e) Carefully remove filter from filtration apparatus and transfer to an aluminumplanchet as a support. Use the same planchet that was used for the determinationof the initial filter weight.f) Dry for at least 1 hr at 102-105 o C in an oven.g) Cool in a desiccator to balance the temperature and weigh.Calculation( A − B) *1000mg total suspended solids/L=samplevolume,mLwhere:A = weight of filter paper and planchet + dried residue (mg) andB = weight of filter paper and planchet (mg).Questions and Data Analysis (Items in BOLD belo are modifications 11/4/08)1. Include a copy of your Lab Notebook pages that record all measurements.2. The TA will determine the COD of all samples. Plot COD versus time for theinfluent and effluent samples on the same figure for all data collected. Use the datafrom every group. On a separate figure, plot the VSS of the reactor versus time,again using the data from each group. (The raw data will be provided to you intabular format by TA.) Assume that VSS ≈ 0.8 TSS. Plot all of your sample data,not the means of the data collected on each day. Your reactor is at steady state whenthe COD and VSS measurements (and wasting volume, see below) no longer changewith time. Based on your data do you think all groups reached equilibrium? Afterhow many days from the start are the reactors in equilibrium? Discuss.If the data are too many to plot all groups on one plot, divide the data and plotseparately.Plot also the wasting volume for each reactor as a function of time. Use thesedata as well as the VSS and COD data to assess if the reactors are at steady-stateconditions.3. Based on the photographs taken in the lab, is there a correlation between whatyou see in the photos and the COD and TSS measurements plotted? Discuss.4. Use the measured flow rate in the reactor and the reactor volume (~ 3.6 l) to computethe mean detention time of the reactor for your lab group.5. Using the data collected after steady-state conditions were achieved (orapproximately steady-state conditions), determine the mean COD +/- 1 estimatedstandard error in the mean for the influent and effluent samples as well as the meanVSS +/- 1 estimated standard error in the mean for the reactor. Perform thiscalculation for data from Groups 1-3 only. For the purpose of this calculation,cstr_reactor_08


6assume steady state was achieved for only the last two sampling days.6. Assuming a Monod model corresponding to equation 14.2 in Water Quality(textbook), the equations developed in class, and data from Groups 1-3, usenonlinear optimization to determine the following parameters: yield factor or yieldcoefficient Y , death rate for bacteria kd, maximum velocity constant k for theMonod model, and half-velocity constant K for the Monod model. (Nonlinearoptimization can be performed in MathCad or MSExcel.) Does your model fit thedata well? If not, what might you change in your model to get a better fit? Discuss.7. Solve for the model parameters in Question 7 by using the Lineweaver-Burkeformulation. See Example 17.1 in text by Droste. Are the best-fit parameters similarto those determined in Question 7? Complete this step only for extra credit.8. You have developed a model to describe the utilization of sodium acetate in yourreactor using data from all groups. In the process of designing a full-scale reactor forthe field you are told that influent substrate concentration will be 1200 mg/L in thefull-scale test. Assume that the full-scale reactor is the same shape as the one used inthe lab, but that you as the engineer can select the size. Assume that the flow rate intothe reactor is 5.5 ml/min, Will the rate coefficients determined in Question 6 apply tothis system as well? What can you do as an engineer to make your reactor achievethe mean effluent substrate concentration of 50 mg/l? Be specific and includecalculations for any necessary changes you would make.ReferencesDroste, R. L., Theory and Practice of Water and Wastewater Treatment, John Wiley &Sons, Inc, New York, 1997.Tchobanoglous, D. and E.D. Schroeder, Water Quality, Addison-Wesley PublishingCompany, 1987.cstr_reactor_08

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