Simultaneous removal of tetrachloroethylene and nitrate with a novel sulfur-packed biocathode system: The synergy between bioelectrocatalytic dechlorination and sulfur autotrophic denitrification

The co-contamination of tetrachloroethylene (PCE) and nitrate is ubiquitous in groundwater, posing a serious threat to human health. The lack of a sustainable electron donor source and the inhibitory effect of nitrate on dechlorination make it difficult to achieve simultaneous removal of PCE and nitrate. Here, a novel process coupling bioelectrocatalytic dechlorination and elemental sulfur (S⁰)-based autotrophic denitrification (eBD-SAD) was established for efficient simultaneous removal of PCE and nitrate. The accelerated nitrate removal in the S⁰-packed biocathode system mitigated the competition for electrons between reductive dechlorination and denitrification. The 95.9% removal of nitrate within 12 h, 87.2% removal of PCE within 48 h, and stable pH of 7.05–7.49 were achieved at an optimized voltage of 0.5 V. The potential dechlorinators (e.g., Pseudomonas, Chryseobacterium, Desulfovibrio, Mesorhizobium, Geobacter) was significantly enriched in the biocathode biofilm. The S⁰ particle biofilm was mainly dominated by denitrifiers (e.g., Arcobacter, Pseudomonas, Azospira, Ralstonia). The positive interactions between electroactive and dechlorination bacteria in the cathode biofilm, as well as the S⁰ autotrophic denitrifiers and non-S⁰-respiring bacteria in the S⁰ particle biofilm, might play important roles in the simultaneous removal of PCE and nitrate. This study proposes a novel method for accelerated electro-biodechlorination by alleviating nitrate competition with the SAD process and opens an appealing avenue for the efficient remediation of groundwater co-contaminated with chlorinated aliphatic hydrocarbons and nitrate.