Anaerobic granules degrading pentachlorophenol (PCP) with specific PCP removal activity up to 14.6 mg/g of volatile suspended solids per day were developed in a laboratory-scale anaerobic upflow sludge blanket reactor at 28°C, by using a...
moreAnaerobic granules degrading pentachlorophenol (PCP) with specific PCP removal activity up to 14.6 mg/g of volatile suspended solids per day were developed in a laboratory-scale anaerobic upflow sludge blanket reactor at 28°C, by using a mixture of acetate, propionate, butyrate, and methanol as the carbon source. The reactor was able to treat synthetic wastewater containing 40 to 60 mg of PCP per liter at a volumetric loading rate of up to 90 mg/liter of reactor volume per day, with a hydraulic retention time of 10.8 to 15 h. PCP removal of more than 99%o was achieved. Results of adsorption of PCP by granular biomass indicated that the PCP removal by the granules was due to biodegradation rather than adsorption. A radiotracer assay demonstrated that the PCP-degrading granules mineralized [14CJPCP to 14CH4 and 14Co2. Toxicity test results indicated that syntrophic propionate degraders and acetate-utilizing methanogens were more sensitive to PCP than syntrophic butyrate degraders. The PCP-degrading granules also exhibited a higher tolerance to the inhibition caused by PCP for methane production and degradation of acetate, propionate, and butyrate, compared with anaerobic granules unadapted to PCP. Pentachlorophenol (PCP) is one of the biocides that was widely used in the United States, mainly for the preservation of wood and wood products. Along with other chlorophe-nols, PCP has been listed as a priority pollutant by the U.S. Environmental Protection Agency (16). Under aerobic conditions , PCP can be degraded by bacteria (2, 8, 29, 34) and fungi (23, 33). Aerobic organisms such as Flavobacterium spp. (8, 34, 37) and Rhodococcus spp. (2, 12, 35) have been successfully used in pilot-scale and field studies for the treatment of PCP-contaminated wastewater and groundwater. PCP can also be completely mineralized to methane and CO2 by anaerobic microorganisms (27). Reductive dechlori-nation of PCP occurs prior to complete mineralization in digested sludges and soils (3, 24, 26-29, 31, 41). Combined systems of an anaerobic fluidized bed plus trickling-filter or aerated lagoons were used to treat chlorophenolic waste from the paper pulp bleaching process (12, 35). Chlorophe-nols were removed from the wastewater by 50 to 60%, and mineralization of added PCP to CO2 was observed by use of radiotracer assay. However, only the overall system removal of chlorophenols was reported, and the role of anaer-obic fluidized bed in dechlorination was not clear. PCP removal or dechlorination was reported in semi-continuous-flow, stirred-sewage sludge digestors (11), in a bioreactor which was partially packed with glass beads to treat a mixture of meta-, ortho-, andpara-chlorophenols (19), in an anaerobic fixed-film reactor (13), and in upflow anaerobic sludge blanket (UASB) reactors with anaerobic granular sludge (14, 28, 42). In some cases, the dechlorination of PCP was not carried out completely, resulting in the appearance of lesser chlorinated phenols (28, 42). The volumetric PCP loading rates of the anaerobic reactor systems mentioned above were ca. 2.2 mg of PCP per liter of reactor volume per day or less. We have developed methanogenic PCP-degrading gran-* Corresponding author. 389 ules on a synthetic wastewater containing PCP, acetate, propionate, butyrate, and methanol in a laboratory-scale UASB reactor at 28°C (5, 6). The maximum PCP removal rate of the granules was as high as 14.6 mg/g of volatile suspended solids (VSS) per day, and a stable volumetric PCP removal rate of 90 mg of PCP per liter per day was achieved. The purpose of this article was to examine the feasibility of the development of methanogenic granules with high dechlorinating activity and to investigate the performance of the granules in treating wastewaters containing high PCP concentrations in a laboratory-scale UASB reactor system. MATERIALS AND METHODS Chemicals and gases. All chemicals (analytical grade) except PCP were obtained from Sigma Chemical Co. (St. Louis, Mo.); PCP was obtained from Aldrich Chemical Co. (Milwaukee, Wis.). Nitrogen gas and gas mixtures of N2-CO2 (95:5 and 70:30) were obtained from Linde Division, Union Carbide Corp. (Warren, Mich.), and passed over heated (370°C) copper filings to remove traces of 02. Analytical methods. Methane, methanol, and volatile fatty acids (VFA) were determined by using gas chromatography as described elsewhere (43, 44). PCP in solution was determined with high-performance liquid chromatography (HPLC). Samples (1.0 ml) were mixed with 0.5 ml of acetonitrile on a vortex mixer, centrifuged for 5 min at 5,500 x g with an Eppendorf 5415 centrifuge (Brinkmann Instruments, Inc., Westbury, N.Y.), and filtered through 0.45-,um-pore-size syringe filters (Acrodisc LC13; Gelman Sciences Co., Ann Arbor, Mich.). A Waters HPLC system, consisting of the model 501 pump, the Lambda-Max model 481 UV detector, and the model 740 data module, was used. Samples were injected by using a Rheodyne 7010 injector fitted with a 50-,ul loop. Separation was accomplished with a Waters Radial-Pak C-18 column. The mobile phase consisted of acetonitrile and 5% aqueous acetic acid (8:2, vol/vol). The flow rate of Vol. 59, No. 2