Efficacy of emerging technologies in addressing reductive dechlorination for environmental bioremediation: A review

Reductive dechlorination is a core pathway of chlorination in an anaerobic environment, which can be carried out by fermentative, methanogenic, iron and sulfate-reducing microorganisms. The present review showed the different metabolic ways of microbes with the emphasis on the anaerobic microbial dechlorination (including chemical, biological and nanotechnology-based strategies), that have been employed to mitigate the chlorinated pollutants. Chemical and nanomaterial science has made substantial advancement in several aspects of dechlorination over the past two decades, providing information about the process and the outcome of the reaction. However, these chemical processes are expensive to start with and pose ecological hazards. So, extensive research has been done to come up with eco-friendly biological alternatives). Under anaerobic conditions, dehalorespiring bacteria are capable of dechlorinating chloroethenes by mediating a stepwise replacement of chlorine with hydrogen resulting in the sequential conversion of perchloroethylene (PCE) to trichloroethylene (TCE), dichloroethylene (DCE) isomers, vinyl chloride (VC), and finally, ethane. Among many dehalorespiring bacterial isolates, only a few strains of the genus Dehalococcoides completely converted the chloroethenes to nontoxic ethane. In the paper we will, therefore, focus on this Dehalococcoides spp. Several factors influence the dechlorination activity between different dehalogenating bacteria. The vcrA and bvcA genes dechlorinate VC into ethene, which are essential for complete dechlorination. These pathways offer understanding of potential bioremediation of chlorinated aliphatic or aromatic compounds by Dehalococcoides with the likelihood of highly effective bioremediation.