Biotechnology and Bioengineering, Vol.59, No.4, 438-444, 1998
Degradation of perchloroethylene and dichlorophenol by pulsed-electric discharge and bioremediation
Pulsed electric discharge (FED) and bioremediation were combined to create a novel two-stage system which dechlorinates the halogenated pollutants, 2,4-dichlorophenol and perchloroethylene, with repetitive (0.1-1 kHz), short pulse (similar to 100 ns), low voltage (40-80 kV) discharges and then mineralizes the less chlorinated products with aerobic bacteria. A 6.1 mM aqueous dichlorophenol sample was cycled through the FED reactor (60 kV of applied pulsed voltage and 300 Hz) 6 times, resulting in the release of 55% of the initial dichlorophenol chloride ions (1 mM Cl- removed each cycle). The respective average specific efficiency is 0.4-0.6 keV/(Cl- molecule). Pseudomonas mendocina KR1, which grows in minimal medium supplemented with phenol but not with dichlorophenol, increased in cell density in all cultures supplemented with the FED-treated DCP samples and yielded a maximum of two-fold additional Cl- released compared to the FED-related alone. The number of FED-treatment cycles, voltage, and frequency were also varied, showing that both cell densities and overall dichlorophenol dechlorination were highly dependent upon the number of FED-treatment cycles, rather than the tested voltages and frequencies. Using this two-stage treatment system, FED released 31% of the initial chloride ions from dichlorophenol (after three cycles at 40-45 kV and 1.2 kHz) while P, mendocina KR1 in the second stage increased dechlorination to 90%. These results were corroborated by the 35% additional chloride release found with activated sludge cultures. Perchloroethylene (0.6 mM) was similarly treated in a first-stage FED reactor (80% chloride removal after four cycles) followed by biodegradation of the dechlorinated products with a recombinant toluene o-monooxygenase-expressing Pseudomonas fluorescens strain. Gas chromatographic analysis showed that the FED reactor created less-chlorinated byproducts (i.e., trichloroethylene) that were removed (74%) upon exposure to the recombinant bacterium.