HW10 PCBs/Pesticides Remediation 10 points Due: Nov. 21

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1 HW10 PCBs/Pesticides Remediation 10 points Due: Nov [2 pts] Given the following PCBs, list the order you would predict them to be biotransformed in an aerobic and anaerobic environment (1 = fastest, 5 = slowest). Would each compound degrade faster aerobically or anaerobically? Why? Compound Aer vs Anaer? Aerobic Environment Anaerobic Environment 2,2 -PCB aer 2 18 of 26 aer strains tested 5 2 Cl, ortho could degrade 3,3 -PCB aer 3 only 2 Cls, either 3 2 Cl, meta dioxygenase o.k.; 15 strains could degrade so 33 didn t signif stop biodeg 4,4 -PCB aer 1 24 of 26 aerobic strains 4 2 Cl, para tested degraded 44 2,2, 4, 4 -PCB anaer 4 2,3 dioxygenase attack 1 4 Cl, para and ortho 3,3, 5, 5 -PCB anaer 5 all meta positions occupied so no dixoygenase access possible! 2 4 Cl, meta First, aerobically the lower chlorinated compounds should degrade faster typically 4 or more Cl must be cometabolically or SLOWLY degraded anaerobically, meta > para > ortho; higher chlorinated faster; lower Cl persistent!

Would each compound degrade faster aerobically or anaerobically? Why? Compound Aer vs Anaer?

2 2. [4 pts] You are a vendor of surfactants and trying to decide which Superfund clean-up contractors to approach to try to sell your product. Given the following sites where bioremediation is being considered, rank the order in which you would visit the sites. Also, what other addition might you recommend to enhance biodegradation at the sites. Justify your response. Compounds Present mixed PCBs (2 to 6 Cl) 0.5 ppm in water mixed PCBs (1-6 Cl), 500 ppm in H2O mono to tri chloro benzene, 5 ppm in H2O Primary Location of Contaminants soil and water in vadose & sat zones soil and water in vadose & sat zones vadose zone and sat zone Rank Additional manipulations to enhance bioremed 3 aerobic; biphenyl 1 anaerobic -> aerobic 4 aerobic DDT, 5 ppb in H2O soil and water 2 anaer -> aer 2,4,5-T; 50 ppm in H2O soil and water 6 anaer Malathion; 50 ppm in water soil and water 5 aerobic Based on partitioning to soil, it appears that the highly chlorinated PCBs and the DDT will sorb most greatly to the soil; followed by chlorobenzenes, malathion, and 245T. If the systems contained high amounts sorbed to the soil, we would expect near-saturation concentrations in the water. Therefore, perhaps low amounts of 245 T, malathion, and chlorobenzenes are sorbed to the soil since the liquid concentrations are below the solubility limits. Using estimated Kp values and the liquid concentrations, the soil sorbed concentrations were calculated (S mass). This shows that very little 245T is sorbed to soil, in which case adding surfactant would do little to significantly increase liquid concentrations. Therefore, rank 245T last in case 2, we are significantly higher than the water solubility, so the ppm in water must include some NAPLs. Therefore, surfactants have a significant ability to dissolve greater concentrations into the soluble water phase. However, GREAT care must to exercised to prevent re-mobilization of the NAPLs, particularly with respect to off-site migration. [some chose to rank NAPL sites last, due to risk to mobilization] DDT is also at it s water solubility (depending on temperature), and there may be NAPLs.

Also, what other addition might you recommend to enhance biodegradation at the sites. Justify your response. Compounds Present mixed PCBs (2 to 6 Cl) 0.

3 Also, between different contaminated sites, those with the worst problems in terms of risk would also be where owners would be willing to spend more to clean up the site (costs associated with surfactant addition). Therefore, compounds with low toxicity and therefore low associated risks would not be good candidates for surfactant application. Drinking water standards will serve as indicators of toxicity. DDT is very toxic, malathion is the least toxic of the contaminants. Therefore, looking at issues of toxicity, sorbed quantities, and soluble concentration, rankings shown in the table were selected. [other answers o.k. with adequate logical support] 3. [4 pts] You are designing biosystems for treatment of contaminated soils in slurry reactors. You are given the following information, and wish to design a reactor for PCB treatment in soil contaminated with Arochlor Total PCB concentration in soil approx. 500 mg/kg.; total mass of contaminated soil = 1000 kg; soil specific gravity 2.5, 1% organic carbon in the soil Note: soil bioslurry reactors are generally operated in batch modes, similar to sequencing batch reactors. You have a mixed consortia of aerobic PCB degraders able to degrade up to 3-Cl-PCB as growth substrates and 4 and 5 Cl PCBs cometabolically. Michaelis-Menton Biokinetics: biphenyl as growth substrate: K = 0.8 g/g-d, Ks = 0.2 mg/l, Y = 0.5 growth substrate PCBs (overall average): K = 0.5 g/g-d, Ks = 0.3 mg/l, Y = 0.2 cometabolic PCBs: K = 0.2 g/g-d, Ks = 0.5 mg/l death from toxicity if total PCB concentration exceeds 10 mg/l in the liquid A consortia of anaerobic bacteria, with first-order biokinetics: rate of transformation of di to 6-Cl PCBs = L/mg-d First-order rate constant describing desorption of PCBs from soil: 0.5 /d where the driving force for desorption is the difference between the equilbrium concentration of PCB in the water and the actual PCB conc in the water a. Would you select an aerobic bioreactor or anaerobic bioreactor? Why? First, look at anticipated composition of chlorines in the PCB mixture - high versus low Arochlor 1248 has an average of 48% Cl by mass, estimate composition (see spreadsheet)

Drinking water standards will serve as indicators of toxicity. DDT is very toxic, malathion is the least toxic of the contaminants.

4 Then, look at anticipated concentrations in the water, assuming max due to equilibrium and/or constant concs with bioactivity Compare rates with either bacterial group - aerobic biodegradation will be significantly faster for the lower chlorinated compounds, while anaerobic is the only biodegradation option for HIGHly chlorinated PCBs. b. How would you ensure an large enough population of active PCB-degrading bacteria in your reactor? First, check for the presence of PCB-degrading bacteria in the contaminated soil to be treated. If sufficient populations of degraders are not present, will need to innoculate the system. if aerobic, add biphenyl as a co-substrate recycle biomass? operate in batch mode with long bio-retention time c. How would you manipulate your design to ensure than the effluent water meets the MCL for PCBs of 0.5 µg/l? Use long enough batch cycle time so that the liquid concentrations are very low, or put effluent water including suspended biomass but excluding soil solids into an aerated CSTR to allow biodegradation without the input of desorbing PCBs. d. How would you ensure that your design meets the regulatory standard for PCBs in soil (assume 2.5 mg/kg)? test the soil, and allow long enough reaction time may need to add surfactants to increase partitioning of PCBs off soil, esp. higher chlorinated PCBs e. Show a sketch of your treatment system (conceptual design) typical range of soil:water ratios 10-50% by weight if assume 30% soil, then 1000 kg soil : 3333 kg water => if 2.5 kg/l density of solids 400 L L water = 3733 L total reactor volume needed = 3.73 m3 for mass transfer of oxygen into liquid depth from surface from mixing, if 1.5 m deep tank (1.3 m water depth), then diameter = 1.9 m => o.k. tank size may require additional oxygen addition during aerobic cycle

First, check for the presence of PCB-degrading bacteria in the contaminated soil to be treated. If sufficient populations of degraders are not present, will need to innoculate the system.

5 during anaerobic cycle, likely need to add sulfate, lactate, hydrogen to encourage necessary reducing conditions... f. What simplifying assumptions would be needed in order to design the system? first, assume biodegradation control, design system, and then check to ensure that desorption rate could keep pace with biodegradation rate assumptions regarding bacterial populations, biokinetics, and interactive effects degrading the PCB mixture g. How would differences between these assumptions and simplifications (also those made in the problem description) and actual conditions affect the reactor performance? if desorption controlled, then would have lower liquid concentrations and longer time needed to remedia`te the soil!

first, assume biodegradation control, design system, and then check to ensure that desorption rate could keep pace with biodegradation rate assumptions regarding bacterial

Bioremediation of contaminated soil. Dr. Piyapawn Somsamak Department of Environmental Science Kasetsart University

Bioremediation of contaminated soil Dr. Piyapawn Somsamak Department of Environmental Science Kasetsart University Outline Process description In situ vs ex situ bioremediation Intrinsic biodegradation