CHLOROPHENOL TOXICITY REMOVAL AND MONITORING IN AEROBIC TREATMENT - RECOVERY FROM PROCESS UPSETS

Bioremediation of simulated groundwater containing 2,4,6-trichlorophen ol (TCP), 2,3,4,6-tetrachlorophenol (TeCP), and pentachlorophenol (PCP ) was studied in a laboratory-scale aerobic fluidized-bed reactor. Chl orophenols were the sole source of carbon and energy in the enrichment culture. At a hydraulic retention time of 5 h and chlorophenol loadin g rate of 445 mg L-1 d-1, stable chlorophenol removal of over 99.7% an d adsorbable organic halogen removal of 99.4% were maintained with the mean inorganic chloride release (ICl) of 94 %. Oxygen consumption tes ts also indicated chlorophenol mineralization. Specific oxygen consump tion decreased in the order: TCP > TeCP > PCP. Endogenous oxygen uptak e rates varied from 3.4 to 4.7 mg oxygen (g of VSS)-1 h-1, correspondi ng to biomass decay rates of 0.06-0.08 d-1. Net biomass yield in the p rocess was 0.03 mg of VSS/mg of CP removed or 0.09 mg of VSS/mg of TOC removed. The effect of interruptions in oxygen supply on process perf ormance and recovery was studied by monitoring chlorophenol concentrat ions and the impact of deteriorating effluent quality on Photobacteriu m phosphoreum (Microtox test). During steady reactor operation, the Mi crotox assay showed no effluent toxicity. The Microtox assay provided a reliable indication of chlorophenol degradation effectiveness. Proce ss upsets were consistently accompanied by increases in effluent PCP c oncentration. Such conditions were detected sensitively and reliably b y the Microtox assay.