Tetrachloroethene (PCE) and trichloroethene (TCE) biodegradation with bioreactors

Chlorinated ethenes have been widely used as solvents and agents in dry cleaning, degreasing, and various manufacturing processes. Before the 1980's, little control on the release and disposal of chlorinated solvents occurred. Many aquifers underlying industrial facilities and United States Department of Defense (DOD) facilities were contaminated by chlorinated solvents. PCE and TCE have gained the most attention because of their widespread occurred and high carcinogenicity. The objective of this research was to develop an aerobic fluidized-bed bioreactor (FBBR), a sequencing anoxic/aerobic batch reactor (SBR), and a sequencing anoxic/aerobic fluidized-bed bioreactor (SFBBR) to effectively dehalogenate PCE and TCE.; The core of this research was the enrichment of mixed microorganisms—denitrifiers and anoxic bacteria with acetate and phenol as substrates—which could survive in a wide range of oxidation and reduction conditions from −300 mV to +100 mV of ORP. The denitrifiers and anoxic bacteria could not only degrade PCE under anoxic conditions and survive in the presence of oxygen (purged with pure oxygen for 10 minutes); but also cometabolize TCE and less-chlorinated ethenes and survive without oxygen.; Aerobic PCE dechlorination was evaluated in an aerobic FBBR. 40% PCE removal was obtained with an inlet PCE concentration of 110 μg/L and a hydraulic retention time of 20 minutes. This is the highest PCE dechlorination rate found in aerobic FBBR as compared to the work of other researchers. In the anoxic/aerobic SBR, a high PCE dechlorination rate was also obtained: 165 ± 18.8 μM-PCE/d for the fast reaction and 0.17 ± 0.06 μM-PCE/d for the slow reaction. In the SFBBR, a stable PCE removal (over 90%) with one day hydraulic detention time was measured. The enriched bacteria after six-month acclimation could dechlorinate PCE completely because no lesser chlorinated ethenes, including TCE, DCE's, and VC were found in the effluent by GC/MS. The steady high PCE and TCE removed rate and microscopic observation of various types of microorganisms showed that the enriched culture was a stable ecosystem. Both SBR and SFBBR could maintain a stable high PCE dechlorination rate. The operation of the SBR is much simpler than the operation of the SFBBR.