Question

1. Excessive usage of pesticides in the golf field in Boryung,ChungNam province (Prof Han’s hometown) have let to severegroundwater contamination, dominated at some locations bycarbofuran (C12H15NO3, MW 221g/mole). Since groundwater is to someextent reused for irrigation purposes, the contamination levelsneed to be reduced to non-toxic levels. A local analyticallaboratory, KAIST & Associates, was contracted to conduct abasic geochemical characterization of the groundwater. Their reportgave the following information:
Total estimated carbofuran contamination: 2,500kg
Average carbofuran concentration: 150mg/L
Available potential electron acceptors: 2mg/L of oxygen (deepaquifers are often fairly depleted in oxygen)
5 mg/L of nitrate
25mg/L of sulfate
negligible amount of bicarbonate (for methanogenesis)
Assuming there are carbofuran-degrading bacteria in this subsurfacesystem, and that recharge is negligible:
A. What will be the prevailing redox conditions in this aquiferwhen carbofuran is degraded to clean standard 5 mg/L?
B. How much total microbial biomass will be produced in thissystem?
C. Calculate the heat losses associated with microbial degradationof carbofuran (in kJ), taking into account that both energy andbiomass are produced, and that energy conversion to ATP is only 40%efficient (Eo’(CO2/carbofuran) = -0.38).
D. A promising remediation strategy for organic contamination isthe use of nitrate to stimulate denitrifying processes, since theseorganisms are almost as efficient as aerobes. How much nitratewould need to be provided to completely degrade carbofuran?