Interaction mechanisms of agricultural waste-driven denitrification and V(V) reduction: Internal electron competition, sequential transfer and activation of vanadium

The co-contamination of NO₃⁻ and V(V) has now become an urgent environmental issue. However, current understanding of the contaminants degradation pathways, the electron competition sequence, and the stability and activation mechanisms of the products in co-pollutant system is relatively limited. In this study, vanadium was found to lead to the accumulation of NO and N₂O. NO₃⁻ and NO₂⁻ were found to promote V activation, while NH₄⁺ facilitated vanadium fixation. Additionally, it was localized that the V reduction products mainly distribute on the cell membrane using TEM-EDX method, facilitating vanadium recovery. The electron competition experiments proved the existence of the electron competition relationship under non-carbon-limiting conditions, confirming the electron competition sequence of NO₃− > NO₂− > V(V). Based on the continuous feeding data for 320 days, the total removal amounts of NO₃⁻ and V(V) was calculated to be 2149.27 mg and 34.80 mg, respectively. Carbon metabolism analysis identified that complete glycolysis, pentose phosphate and TCA cycle pathways provided sufficient electrons and energy for pollutants reduction. These findings provide in-depth insights into the interaction mechanisms of N, V, and C metabolism in groundwater systems and have significant implications for the bioremediation of co-contaminated groundwater by NO₃⁻ and V(V).