Bioremediation of contaminated waters via microbial electrochemical reactions

Industrial applications have contaminated environmental waters with complex mixtures of anthropogenic toxic compounds, including chlorinated hydrocarbons and heavy metals. Microbial populations at the contaminated sites can often naturally convert toxic contaminants into harmless end- products, but the efficiency of the remediation can be limited by lack of suitable electron donors or acceptors. Certain micro-organisms can exchange electrons directly or via a mediator with solid matter, such as an electrode in an electrochemical system. This enables the conversion of the chemical energy stored in the contaminants to electrical energy. Alternatively, electrical energy can be used to drive the microbial degradation of the contaminants. Bio-electrochemical systems were inoculated with sediment samples collected from environmental sites contaminated with metals or organic pollutants to enrich electroactive microbial cultures capable of efficient degradation of the contaminants. The enrichment was done in two-chamber bio-electrochemical systems with either bioanodes (for oxidisable contaminants) and/or biocathodes (for reducible contaminants). The required electrical energy input or obtainable output was measured using linear sweep voltammetry. The success of the enrichment was confirmed by the increasing electrical current output. The microbial communities in the original sediment samples and in the enriched biofilms were analysed in order to assess their metabolic potential and the possibilities to improve the remediation efficiency through the modification of the composition of the microbial communities using e.g. selective pressures. This research was done as a part of GREENER -project (InteGRated systems for Effective ENvironmEntal Remediation), developing green and sustainable low-cost bioremediation technologies. The project has received funding from the European Union’s Horizon 2020 Research and Innovation Programme under grant agreement No. 826312