Enhanced microbial dechlorination of PCBs by anaerobic digested sludge and enrichment of low-abundance PCB dechlorinators

Abstract

The slow rate of anaerobic microbial dechlorination in natural environments limits the application of polychlorinated biphenyl (PCB) bioremediation. Anaerobic digested sludge (ADS), abundant in nutrients and microorganisms, could be an effective additive to improve microbial dechlorination. This research investigates the influence of ADS on Aroclor 1260 dechlorination performance, microbial community composition, and the abundance of functional genes. Moreover, further enrichment of organohalide-respiring bacteria (OHRB) was examined using tetrachloroethene (PCE) as the electron acceptor, followed by the serial dilution-to-extinction method in conjunction with resuscitation promoting factor (Rpf) supplementation. The results demonstrated that the addition of 5 g/L ADS achieved more extensive and efficient dechlorination of PCBs. ADS enhanced the removal of meta- and para-chlorine without significantly changing the dechlorination pathways. The abundances of dechlorinators, including Dehalobium and Dehalobacter within the Chloroflexi and Firmicutes phyla, as well as non-dechlorinators from the Desulfobacterota, Euryarchaeota, and Bacteroidetes phyla, were significantly increased with ADS amendment. Similarly, an increased abundance of bacteria, OHRB, reductive dehalogenase (RDase) genes, and archaeal 16S rRNA genes was observed. Additionally, obligate OHRB, such as Dehalobacter and Dehalobium, were further enriched. These findings indicate that ADS effectively enhances microbial reductive dechlorination and highlight the potential for enriching and isolating OHRB with Rpf.