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 pentachlo rophenol (PCP) containing wastes using sequential anaerobic and aerobi c biodegradation. Anaerobically, PCP was degraded to predominately equ imolar concentrations (>99%) of monochlorophenol (MCP) in two GAC flui dized bed reactors at Empty Bed Contact Times (EBCTs) ranging from 18. 6 to 1.15 hours. However, at lower EBCTs, MCP concentrations decreased to less than 10% of the influent PCP concentration suggesting mineral ization. The optimal EBCT was determined to be 2.3 hours based on PCP conversion to MCPs and stable reactor operation. Decreasing the EBCT f ourfold did not inhibit degradation of PCP and its intermediates, thus allowing removal of PCP at much lower detention time and resulting in a significant cost advantage. Analytical grade PCP was fed via syring e pumps into two fluidized bed reactors at influent concentrations of 100 mg/l and 200 mg/l, respectively. Acting as the primary substrate, ethanol was also fed into the reactors at concentrations of 697 and 13 88 mg/l. Effluent PCP and chlorinated phenolic compounds were analyzed weekly to evaluate reactor performance. Biodegradation pathways were also identified. 3-chlorophenol (CP) was the predominant MCP and varie d simultaneously with 3,5-dichlorophenol (DCP) concentrations. Likewis e, 4-CP concentrations varied simultaneously with 3,4-DCP concentratio ns. A second stage aerobic GAC fluidized bed reactor was added after t he anaerobic reactor to completely mineralize the remaining MCP and ph enols. Data show no presence of phenol and MCP in the effluent or on t he GAG. Overall, the chemical oxygen demand (COD) fed to the system wa s reduced from 75 g/d in the influent to less than 1.5 g/d in the effl uent. (C) 1997 IAWQ. Published by Elsevier Science Ltd.