Nitrate enhances TCE removal by enriching bifunctional denitrifying/aerobic co-metabolizing microbes in the joint H2/O2 system

Abstract

Trichloroethylene (TCE) is a pervasive groundwater contaminant that poses significant health and ecological safety risks. The coexistence of hydrogen (H₂) and oxygen (O₂), resulting from electrochemical remediation technologies, has been shown to promote the degradation of TCE by fostering specific microbial communities. However, the role of nitrate (NO₃⁻), a common co-contaminant with TCE in groundwater, in this H₂/O₂ system remains poorly understood. This study revealed that increasing the nitrate concentrations (0–240 mg L⁻¹) significantly enhanced TCE removal rate and efficiency, with the maximum removal rate increased by 1.84 times and removal efficiency by 19.79%. The variation in nitrate concentration could influence microbial diversity. In particular, denitrifying microorganisms, such as Pseudomonas, Hydrogenophaga, and Methyloversatilis, were enriched, which could reduce nitrate and nitrite using H₂ as an electron donor and degrade TCE through aerobic co-metabolism. The increased presence of these microorganisms led to an abundance of the functional gene phe, which is responsible for TCE aerobic co-metabolic degradation, thereby enhancing TCE removal in the joint H₂/O₂ system. However, a high nitrate concentration of up to 240 mg L⁻¹ inhibited the accumulation of Pseudomonas and Methyloversatilis. Meanwhile, it increased the abundance of Hydrogenophaga, which could use H₂ and O₂ to fix CO₂ and provide organics for bacterial growth. These insights provide valuable technical guidance for the remediation of TCE and nitrate composites in groundwater environments, highlighting the potential of leveraging the interactive effects of H₂, O₂, and nitrate on microbial communities for effective bioremediation strategies.