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 pentachlorophenol (PCP) containing wastes using sequential anaerobic and aerobic biodegradation. Anaerobically, PCP was degraded to approximately equimolar concentrations (>99%) of chlorophenol (CP) in a granular activated carbon (GAC) fluidized bed reactor (FBR) at empty bed contact times (EBCTs) ranging from 18.6 to 2.3 hr. However, at lower EBCTs, chlorophenol concentrations decreased 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 operation. Decreasing the EBCT fourfold did not inhibit degradation of PCP and its intermediates, and thus, removal of PCP is possible at lower detention times providing a significant cost advantage.

Analytical grade PCP was fed via syringe pumps into a GAC FBR at an influent concentration of 200 mg/L. Acting as the primary substrate, ethanol was also fed at a concentration of 1388 mg/L. Effluent PCP and chlorinated phenolic compounds were analyzed weekly to evaluate reactor performance. Biodegradation pathways were also identified. 3-chlorophenol (3-CP) was the predominant CP. Concentrations of 3-CP follow the same trends as 3,5-dichlorophenol (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 which removed the remaining CP and phenols. No phenol or CP has been observed in the effluent or on the GAC. Overall, the influent chemical oxygen demand (COD) loading was reduced from 34 g/L*d to less than 1.36 g/L*d.