Dong-Mei Yang ¹ Fen-Li Min ² Ying Li ¹ Jia-Lu Ling ¹ Hui-Xian Zhong ¹ Yu-Chun Xia ¹ Ying Feng ¹ Li-Ya Zhao ¹ Zhao-Hua Li ¹ Li-Lian Wen ^1*

• ¹ Hubei University, Wuhan, Hubei Province, China
• ² Jianghan University, Wuhan, Hubei Province, China

Bioremediation at Trichloroethene (TCE) contaminated sites often leads to groundwater acidification, while at nitrate polluted sites generates alkalization. TCE and nitrate often coexist in the contaminated sites, but the pH variation caused by nitrate self-alkalization and TCE self-acidification and how these processes affect nitrate reduction and reductive dechlorination have not been studied. This study investigated the interaction of nitrate and TCE, two common groundwater co-contaminants, during bio-reduction in serum bottles with synthetic mineral salts media and microbial consortia. Our results showed that TCE concentrations up to 0.3 mM stimulated nitrate reduction, while the effect of nitrate on TCE reductive dechlorination was complex. Nitrate primarily inhibited the reduction of TCE to dichloroethene (DCE), but enhanced the reduction of vinyl chloride (VC) to ethene. Mechanistic analysis suggested that the inhibition was due to the thermodynamic favorability of nitrate reduction over TCE reduction, while the promotion of VC reduction was linked to pH stabilization via self-alkalization. As the initial nitrate concentration increased from 0 to 3 mM, the relative abundance of putative denitrifying genera Petrimonas and Trichlorobacter rose, whereas fermenter Clostridium abundance declined dramatically from 31.11% to 1.51%, indicating the strong nitrate inhibition. Additionally, the relative abundance of Dehalococcoides, the known genus that is able to reduce TCE all the way to ethene, slightly increased from 23.91% to 24.26% when nitrate concentration up to 0.3 mM, but decreased to 18.65% when the nitrate concentration increased to 3 mM, suggesting the Dehalococcoides was tolerant to a high concentration of nitrate under certain conditions. Overall, our findings highlight the potential for simultaneous reduction of TCE and nitrate even at elevated concentrations, facilitated by self-pH control in anaerobic mixed dechlorinating consortia, providing new insights for bioremediation strategies in contaminated sites.