Anaerobic/aerobic biodegradation of pentachlorophenol using GAC fluidized bed reactors: Optimization of the empty bed contact time

An integrated reactor system has been developed to remediate pentachlorophe nol (PCP) containing wastes using sequential anaerobic and aerobic biodegra dation. Anaerobically, PCP was degraded to approximately equimolar concentr ations (>99%) of chlorophenol (CP) in a granular activated carbon (GAC) flu idized bed reactor (FBR) at empty bed contact times (EBCTs) ranging from 18 .6 to 2.3 hr. However, at lower EBCTs, chlorophenol concentrations decrease d to less than 10% of the influent PCP concentration. The optimal EBCT was determined to be 2.3 hr based on PCP conversion to CPs and stable reactor o peration. Decreasing the EBCT fourfold did not inhibit degradation of PCP a nd its intermediates, and thus, removal of PCP is possible at lower detenti on times providing a significant cost advantage. Analytical grade PCP was fed via syringe pumps into a GAC FBR at an influen t concentration of 200 mg/L. Acting as the primary substrate, ethanol was a lso fed at a concentration of 1388 mg/L. Effluent PCP and chlorinated pheno lic compounds were analyzed weekly to evaluate reactor performance. Biodegr adation pathways were also identified. 3-chlorophenol (3-CP) was the predom inant CP. Concentrations of 3-CP follow the same trends as 3,5-dichlorophen ol (DCP) concentrations. In a similar manner, 4-chlorophenol concentrations correlate with 3,4-DCP concentrations. A second stage aerobic GAC FBR was added after the anaerobic bioreactor whi ch removed the remaining CP and phenols. No phenol or CP has been observed in the effluent or on the GAG. Overall, the influent chemical oxygen demand (COD) loading was reduced from 34 g/L*d to less than 1.36 g/L*d. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.