Excessive usage of pesticides in the golf field in Boryung, ChungNam province (Prof Han's hometown) have let to severe groundwater contamination, dominated at some locations by carbofuran (C12H15NO3, MW 221g/mole). Since groundwater is to some extent reused for irrigation purposes, the contamination levels need to be reduced to non-toxic levels. A local analytical laboratory, KAIST & Associates, was contracted to conduct a basic geochemical characterization of the groundwater. Their report gave the following information:
Total estimated carbofuran contamination: 2,500kg
Average carbofuran concentration: 150mg/L
Available potential electron acceptors: 2mg/L of oxygen (deep aquifers 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 subsurface system, and that recharge is negligible:
A. What will be the prevailing redox conditions in this aquifer when carbofuran is degraded to clean standard 5 mg/L?
B. How much total microbial biomass will be produced in this system?
C. Calculate the heat losses associated with microbial degradation of carbofuran (in kJ), taking into account that both energy and biomass 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 is the use of nitrate to stimulate denitrifying processes, since these organisms are almost as efficient as aerobes. How much nitrate would need to be provided to completely degrade carbofuran?