A reactor system combining reductive dechlorination with co-metabolic oxidation for complete degradation of tetrachloroentylene.

A laboratory sequential anaerobic-aerobic bioreactor system, which consisted of an anaerobic fixed film reactor and two aerobic chemostats, was set up to degrade tetrachloroethylene (PCE) without accumulating highly toxic degradation intermediates. A soil enrichment culture, which could reductively dechlorinate 900 microM (ca. 150 mg/L) of PCE stoichiometrically into cis-1,2-dichloroethylene (cis-DCE), was attached to ceramic media in the anaerobic fixed film reactor. A phenol degrading strain, Alcaligenes sp. R5, which can efficiently degrade cis-DCE by co-metabolic oxidation, was used as inoculum for the aerobic chemostats consisted of a transformation reactor and a growth reactor. The anaerobic fixed film bioreactor showed more than 99% of PCE transformation into cis-DCE in the range of influent PCE concentration from 5 microM to 35 microM at hydraulic retention time of 48 h. On the other hand, efficient degradation of the resultant cis-DCE by strain R5 in the following aerobic system could not be achieved due to oxygen limitation. However, 54% of the maximum cis-DCE degradation was obtained when 10 mumol of hydrogen peroxide (H2O2) was supplemented to the transformation reactor as an additional oxygen source. Further studies are needed to achieve more efficient co-metabolic degradation of cis-DCE in the aerobic reactor.