Chlorophenol Toxicity Removal and Monitoring in Aerobic Treatment: Recovery from Process Upsets

Bioremediation of simulated groundwater containing 2,4,6-trichlorophenol (TCP), 2,3,4,6-tetrachlorophenol (TeCP), and pentachlorophenol (PCP) was studied in a laboratoryscale aerobic fluidized-bed reactor. Chlorophenols were the sole source of carbon and energy in the enrichment culture. At a hydraulic retention time of 5 h and chlorophenol loading rate of 445 mg L⁻¹ d⁻¹, stable chlorophenol removal of over 99.7% and adsorbable organic halogen removal of 99.4% were maintained with the mean inorganic chloride release (ICI) of 94%. Oxygen consumption tests also indicated chlorophenol mineralization. Specific oxygen consumption decreased in the order: TCP > TeCP > PCP. Endogenous oxygen uptake rates varied from 3.4 to 4.7 mg oxygen (g of VSS)⁻¹ h⁻¹, corresponding to biomass decay rates of 0.06–0.08 d⁻¹. Net biomass yield in the process 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 performance and recovery was studied by monitoring chlorophenol concentrations and the impact of deteriorating effluent quality on Photobacterium phosphoreum (Microtox test). During steady reactor operation, the Microtox assay showed no effluent toxicity. The Microtox assay provided a reliable indication of chlorophenol degradation effectiveness. Process upsets were consistently accompanied by increases in effluent PCP concentration. Such conditions were detected sensitively and reliably by the Microtox assay.