Purification of groundwater contaminated with chlorinated ethenes using biochar-amended biofilters

The biofilter (BF) has been explored as a potential tool for groundwater remediation, offering the prospect of self-renewal of the sorbent's sorption capacity through the microbial degradation of introduced contaminants, as well as the utilisation of eco-friendly filter materials, such as biochar. To elaborate, column experiments were conducted utilising two distinct types of biochar (A750, W550) and activated carbon (AC), inoculated with two types of microbial communities (kb1, iH), which have been demonstrated to be capable of complete reductive dechlorination of tetrachloroethene (PCE) to ethene. The monitoring methods employed included compound-specific isotope analysis (CSIA), 16S rRNA gene sequencing, microbial phospholipid-derived fatty acid (PLFA) analysis, and desorption of chlorinated ethenes (CE) from the filter materials. The results indicated that the conversion of PCE into ethene was most efficient for the BFs filled with biochars. All sorbents exhibited comparable retention of cis-dichloroethene (cDCE) and vinyl chloride (VC), while AC demonstrated predominant sorption of PCE and trichloroethene (TCE). A comparison of DNA sequencing and PLFA analysis from the sorbent samples revealed their impact on microbial community composition, suggesting that microorganisms may proliferate more readily on biochar compared to AC. In essence, a functional BF requires both an adaptable microbial community and a corresponding sorbent material. In conclusion, the application of a BF shows great promise as an alternative groundwater remediation technology, ready for further testing at pilot scale. • The designed biofilters enabled complete dechlorination of PCE to ethene. • Biochar favoured bioavailability of PCE and PCE metabolites over activated carbon. • The microbial transfer potential of cobalamins supported the formation of ethene. • Self-sustaining sorption capacity could be achieved using biochar and microbes.