| Pentachlorophenol (PCP) is a biocide which is widely used for its toxicity to microorganisms. Its major application is in wood preservation, and PCP at abandoned wood preserving sites is a major source of environmental pollution. Although much of the literature documents aerobic treatment for PCP, research indicates that there is great potential for anaerobic dechlorination of these compounds. The objectives of this investigation were to study the acidogenesis phase of the anaerobic biodegradation process; how acidogenesis is affected by PCP toxicity alone and in the presence of zinc; what role acidogenesis plays in the biodegradation of PCP; and how operating parameters, such as organic loading rate (OLR) and solids retention time (SRT) affect the degradation of PCP during acidogenesis. Batch anaerobic toxicity assays (ATAs) were performed to quantify the toxicity threshold for PCP and zinc, and to study the effect of these toxicants on volatile acids production. Continuous reactors (chemostats) were operated at SRTs of 0.25-0.61 day to kinetically exclude methanogenesis from acetate, so that the effects of the toxicants on acidogenesis could be evaluated.;PCP was found to have a toxicity threshold of 2.7-3.0 mg/L and zinc 23-27 mg/L in batch systems. Acetate utilizers showed the first signs of inhibition in PCP spiked systems, whereas hydrogen utilizers were the first organisms affected in response to a zinc spike. In the continuous systems, PCP in spike concentrations of 7.0 mg/L did not affect the quantity or composition of volatile acids produced in the chemostats. A rise in headspace hydrogen at 30 mg/L zinc indicated that hydrogen utilizers became inhibited in the presence of high zinc concentrations.;PCP was degraded, with approximately half of the degradation occurring during acidogenesis. GC/MS analysis detected no intermediate chlorophenols in the effluent. The efficiency of degradation varied indirectly with spike concentration and directly with SRT. |
