Sequential Anaerobic/Aerobic Microbial Transformation of Chlorinated Ethenes: Use of Sustainable Approaches for Aquifer Decontamination

Chlorinated ethene contamination is a worldwide relevant health issue. In anaerobic aquifers, highly chlorinated ethenes are transformed by microbially-mediated organohalide respi- ration metabolism. For this reason, in the last few years, bioremediation interventions have been developed and employed in situ for aquifer decontamination. Biostimulation has been demonstrated to be efficient in enhancing organohalide respiration activity. The use of agrifood wastes that replace engineered substrates as biostimulants permits the low carbon impact of bioremediation treatment as part of a circular economy approach. The present work depicts the effects of available bio-based substrates and discusses their efficiency and impact on microbial communities when applied to con- taminated aquifers. As a drawback of anaerobic organohalide respiration, there is the accumulation of more toxic lower-chlorinated ethenes. However, compounds such as dichloroethene (DCE) and vinyl chloride (VC) can be mineralized by metabolic and co-metabolic pathways in aerobic condi- tions. For this reason, sequential anaerobic/aerobic treatments proposed to stimulate the natural biotransformation activity can achieve complete degradation of chlorinated ethenes. The aim of this work is to provide an up-to-date revision of anaerobic/aerobic microbial transformation pathways towards chlorinated ethenes and to discuss their application in real scenarios and futurable microbial bioelectrochemical systems to remediate contaminated aquifers.