The enhanced degradation of trichloroethylene in the bioelectrochemical system integrated with iron‑carbon micro-electrolysis

Abstract

Trichloroethylene (TCE) is one of the most abundant volatile chlorinated hydrocarbons in groundwater which threatens human health and the environment. Utilizing a bioelectrochemical system (BES) to treat TCE is a promising strategy; however, as the ionic strength of the groundwater is low and the extracellular electron transfer of BES is limited, BES degradation of TCE is impeded. In this research, iron and graphite were added to the cathode chamber to form a micro-electrolysis to enhance the degradation of TCE synergistically. The results showed that when the iron and carbon mixture dosage was 70 g/L with the mass ratio (Fe/C) of 1:2 and the initial TCE concentration of 100 mg/L, the degradation efficiency of BES reached 97.8 % at the cathodic potential of −0.3 V (vs.SHE). This was 1.31 times, 1.94 times, and 2.74 times that of Fe/C + open-circuit BES, Fe/C micro-electrolysis, and conventional BES without Fe/C, respectively, which implied that iron‑carbon mediated BES colligated the advantages of microbial degradation and micro-electrolysis, and iron‑carbon provided more electrons and accelerated electron transfer to improve the degradation of TCE significantly. Moreover, through the analysis of the microorganisms of Fe/C + BES, the highest abundances of microorganisms at phylum, class, and genus levels were Proteobacteria, Alphaproteobacteria, and Acetobacterium, respectively. By comparing Fe/C + BES with conventional BES, the addition of iron‑carbon enhanced the microbial diversity and species richness and improved the abundances of Pseudomonas and Geobacter at the genus level. In all, iron‑carbon micro-electrolysis can be integrated with BES to treat TCE and facilitate BES application in the volatile chlorinated hydrocarbon-contaminated sites.