Electrical stimulation of microbial PCB degradation in sediment

Abstract

Bioremediation of polychlorinated biphenyls (PCBs) has been precluded in part by the lack of a cost-effective method to stimulate microbial degradation in situ. A common limitation is the lack of an effective method of providing electron donors and acceptors to promote in situ PCB biodegradation. Application of an electric potential to soil/sediment could be an effective means of providing electron-donors/-acceptors to PCB dechlorinating and degrading microorganisms. In this study, electrical stimulation of microbial PCB dechlorination/ degradation was examined in sediment maintained under simulated in situ conditions. Voltage was applied to open microcosms filled with PCB-impacted (Aroclor 1242) freshwater sediment from a Superfund site (Fox River, WI). The effect of applied low voltages (1.5 to 3.0V) on the microbial transformation of PCBs was determined with: 1) spiked PCBs, and 2) indigenous weathered PCBs. The results indicate that both oxidative and reductive microbial transformation of the spiked PCBs was stimulated but oxidation was dominant and most effective with higher voltage. Chlorobenzoates were produced as oxidation metabolites of the spiked PCBs, but increasing voltage enhanced chlorobenzoate consumption, indicating that overall degradation was enhanced. In the case of weathered PCBs, the total concentration decreased 40–60% in microcosms exposed to electric current while no significant decrease of PCB concentration was observed in control reactors (0 V or sterilized). Single congener analysis of the weathered PCBs showed significant loss of di- to penta-chlorinated congeners, indicating that microbial activity was not limited to anaerobic dechlorination of only higher chlorinated congeners. Degradation was most apparent with the application of only 1.5 V where anodic O2 was not generated, indicating a mechanism of degradation independent of electrolytic O2. Low voltage stimulation of the microbial degradation of weathered PCBs observed in this study suggests that this approach could be a cost-effective, environmentally sustainable strategy to remediate PCBs in situ.

Enhanced ex-situ bioremediation of soil contaminated with petroleum refinery waste effluents by biostimulation through electrokinetics and inorganic fertilizer

“…Thus, TOC removal increased with increase in applied voltage. This is in agreement with the observation of Chun et al [11] for the electrical stimulation of microbial PCB degradation in sediment. In recent years, several studies have reported that there was neither negative nor positive effects observed by applying current (3.14 A/m 2 ) on soil bacteria [14,32].…”

“…That is, no removal of TOCs was observed in sterilized control. A similar observation has been reported for polychlorinated biphenyl (PCB) [11]. Also, there was no significant difference in the TOC concentration in sample Cathode Section soil with the distances from anode.…”

“…Several methods to supply electron donors and acceptors into subsurface environments have been proposed including direct gas addition techniques such as, sparging of gases and membrane-supplied gas [7 -8] and the addition of liquid and solid chemicals which could be fermentable substrates, organic and inorganic fertilizers, Fe species, oxygen and hydrogen-releasing compounds [9 -10]. Nonetheless, these methods require periodic reapplication to sustain its amendment's effect; because chemical compounds and gases added to the subsurface easily diffuse away and are consumed through abiotic reactionsand the delivery system can be costly [11]. Therefore, a new method or approach that can provide a continuous source at a controlled rate in situ is needed.…”

Electro-assisted groundwater bioremediation: Fundamentals, challenges and future perspectives

“…The basic concept of electro-assisted bioremediation of groundwater is to place polarized electrodes into the contaminated aquifer (Chun et al, 2013;Zhang et al, 2010). The contaminant removal could be electrochemically enhanced through several mechanisms.…”

Improved 4-chlorophenol dechlorination at biocathode in bioelectrochemical system using optimized modular cathode design with composite stainless steel and carbon-based materials

“…In order to treat wastewater in more sustainable way, bioelectrochemical system (BES) was introduced to achieve this goal for its resource recovery from wastewater and low energy consumption (Friman et al, 2013;Kong et al, 2014a;Liang et al, 2013;Wang et al, 2011). It has been demonstrated that BES is of great potential for the dechlorination, including reduction at anode and cathode (Aulenta et al, 2011;Chun et al, 2013;Huang et al, 2012;Kong et al, 2014b;Wen et al, 2013). Taking the reduction role of cathode into account, the electrons produced from anode are transferred via the external circuit to the cathode where it reduces the electron acceptor.…”