Regulating the dechlorination and methanogenesis synchronously to achieve a win-win remediation solution for γ-hexachlorocyclohexane polluted anaerobic environment

The wish for rapid degradation of chlorinated organic pollutants along with the increase concern with respect to greenhouse effect and bioenergy methane production have created urgent needs to explore synchronous regulation approach. Microbial electrolysis cell was established under four degressive cathode potential settings (from-0.15V to-0.60V) to regulate gamma-hexachlorocyclohexane (gamma-HCH) reduction while CH4 cumulation in this study. The synchronous facilitation of gamma-HCH reduction and CH4 cumulation was occurred in-0.15V treatment while the facilitation of gamma-HCH reductive removal together with the inhibition of CH4 cumulation was showed in-0.30V treatment. Electrochemical patterns via cyclic voltammetry and morphological performances via scanning electron microscopy illustrated bioelectrostimulation promoted redox reactions and helped to construct mature biofilms located on bioelectrodes. Also, bioelectrostimulated regulation pronouncedly affected the bacteria and archaeal communities and subsequently assembled distinctly core sensitive responders across bioanode, biocathode and plankton. Clostridum, Longilinea and Methanothrix relatively accumulated in the plankton, and Cupriavidus and Methanospirillum, and Perimonas and Nonoarcheaum in biocathode and bioanode, respectively; while Pseudomonas, Stenotrophomonas, Methanoculleus and Methanosarcina were diffusely enriched. Microbial interactions in the ecological network were more complicated in-0.15V and-0.30V cathodic potential treatments, coincident with the increasement of gamma-HCH reduction. The co-existence between putative dechlorinators and methanogens was less significant in-0.30V treatment when compared to that in-0.15V treatment, relevant with the variations of CH4 cumulation. In all, this study firstly corroborated the availability to synchronously regulate gamma-HCH reductive removal and methanogenesis. Besides, it paves an advanced approach controlling gamma-HCH reduction in cooperation with CH4 cumulation, of which to achieve gamma-HCH degradation facilitation along with biogas (CH4) production promotion with-0.15V cathode potential during anaerobic gamma-HCH contaminated wastewater digestion, or to realize gamma-HCH degradation facilitation with the inhibition of CH4 emission with-0.30V cathode potential for an all-win remediation in gamma-HCH polluted anaerobic environment such as paddy soil.

Automated summary

The study confirmed the feasibility of synchronously regulating the reduction of γ-HCH and methanogenesis, with different effects achieved based on the cathodic potential setting. Bioelectrostimulation regulation can promote redox reactions, influence microbial communities, and lead to more complicated microbial interactions in the ecological network.