Complete mineralization of 501),M of pentachloropheriol (PCP) was achieved anaerobically under continuous flew conditions using two columns connected in series with a hydraulic retention time of 14 2 days, showing the highest reported mineralization rate yet of 3 5 mu M day(-1) 1 he first column, when injected with a reductive PCP dechlonnating consortium, dechlonnated PCP to mainly phenol and traces of 3 chlorophenol (3-CP) using lactate supplied continuously as an electron donor The second column with an anaerobic phenol degrading consortium decomposed phenol and 3-CP under iron reducing conditions with substantial fermentative degradation of organic compounds When 20 mM of lactate was introduced into the first column, the phenol degiadation activity of the second column w is lost in a short period of time because the amorphous Fe(III) oxide (FeOOH) that had been packed in the column before use was depleted by lactate metabolites, such as acetate and propionate flowing into the second column from the first column The complete mineralization of PCP was maintained for t long period by reducing the lactate concentration to 4 mM, effectively extending the longevity of second-column activity with no depletion of FeOOH for more than 200 pore volumes (corresponding to 3 000 days) The carbon balance showed that 50 mu M PCP and 4 mM lactate in the Influent had transformed to CO2 (81%) and CH4 (3%) and had contributed to biomass growth (8%) A comparison of the microbial consortia introduced into the columns and those flowing out from the columns suggested that the introduced population did not flow out during the experiments, although the microbial composition of the phenol column was considered to be affected by the inflow of microbes from the PCP dechlorination column These results suggest that a sequential combination of reductive dechlonnating and anaerobic oxidizing consortia is useful for anaerobic remedistion of chlorinated aromatic compounds in a microbial permeable reactive barrier Biotechnol Bioeng 2010,107 775-785 (C) 2010 Wiley Periodicals, Inc