Complete anaerobic mineralization of pentachlorophenol (PCP) under continuous flow conditions by sequential combination of PCP‐dechlorinating and phenol‐degrading consortia

Abstract

Complete mineralization of 50 µM of pentachlorophenol (PCP) was achieved anaerobically under continuous flow 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 µM day(-1). The first column, when injected with a reductive PCP dechlorinating consortium, dechlorinated 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 degradation activity of the second column was 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 a 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 µM PCP and 4 mM lactate in the influent had transformed to CO(2) (81%) and CH(4) (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 dechlorinating and anaerobic oxidizing consortia is useful for anaerobic remediation of chlorinated aromatic compounds in a microbial permeable reactive barrier.

Anaerobic mineralization of 2,4,6-tribromophenol to CO2 by a synthetic microbial community comprising Clostridium, Dehalobacter, and Desulfatiglans

“…Additionally, the chemical concentrations used in the synthetic community in this study were much lower than those used in previous reports, i.e. 4 or 20 mM lactate, 20 mM FeO-OH, 20 mM SO 4 2- (Yang et al, 2009;Li et al, 2010Li et al, , 2013, and would avoid excessive resource consumption and decrease cost. Previous studies have reported the microbial degradation of 2,4,6-TBP aerobically or anaerobically (Ahn et al, 2003;Boyle et al, 1999;Uhnakova et al, 2009;Yamada et al, 2008).…”

“…In our previous study, we demonstrated the mineralization of pentachlorophenol (PCP) by co-inoculation of multiple consortia: one reductively dechlorinating PCP and another anaerobically oxidizing the dehalogenated metabolites (less-chlorinated phenols) in a batchtype culture (Yang et al, 2009) and continuous-flow reactors (Li et al, 2010. These results indicated that functionallydesigned communities prepared by co-inoculating multiple consortia are a promising application of anaerobic systems.…”

“…Due to predefined characteristics, the mineralization process did not cause any secondary byproducts, which improved the management and efficiency of the system, compared to the method of inoculating undefined, mixed cultures in previously reported mineralization systems, where most of the population in the community were not involved in the mineralization process. (Yang et al, 2009;Li et al, 2010Li et al, , 2013. Restricting such unnecessary microorganisms in the reaction mixture would increase the efficiency and achieve better control of the system.…”

“…However, in these combined consortia, the microbial communities were complex and included very small populations of important, functional populations such as dehalogenators and aromatic-oxidizers (Li et al, 2010. Some secondary microbial reactions occurred (Yang et al, 2009) and disturbed the mineralization process, or even rendered the system ineffective (Li et al, 2010). However, the synthetic microbial community, constructed using isolates or highly enriched microorganisms, is expected to overcome these challenges (De Roy et al, 2014).…”

“…These results indicated that functionallydesigned communities prepared by co-inoculating multiple consortia are a promising application of anaerobic systems. However, in these combined consortia, the microbial communities were complex and included very small populations of important, functional populations such as dehalogenators and aromatic-oxidizers (Li et al, 2010. Some secondary microbial reactions occurred (Yang et al, 2009) and disturbed the mineralization process, or even rendered the system ineffective (Li et al, 2010).…”