Resource Recovery of Corn Stover in Water Treatment: Nitrate Removal from Simulated Groundwater
This study evaluated the sustainability and tissue-specific mechanisms of corn stover as a solid-phase carbon source for nitrate removal from groundwater. Cyclic heterotrophic denitrification experiments were conducted using leaf, stem pith, stem bark, stem node, husk, and mixed tissues as carbon sources. Denitrification efficiency, sustainability, dissolved organic carbon (DOC) release, carbon utilization efficiency, intermediate accumulation, and environmental parameters were systematically assessed. Kinetic modeling, correlation analysis, and structural equation modeling (SEM) were applied to elucidate regulatory mechanisms. Results demonstrated that mixed tissues and husk achieved the highest denitrification efficiency, with nitrate removal rates consistently above 98% across four repeated cycles. Total nitrogen removal reached 39.30 mg/g for mixed tissues and 39.95 mg/g for husk, while byproduct concentrations (NO2-N and NH4-N) remained below 2 mg/L. DOC release profiles indicated stable carbon release and high carbon utilization efficiency (203.99 mg TN/g organic carbon for mixed tissues; 182.41 mg/g for husk). Correlation and SEM analyses revealed that carbon source type indirectly governed total nitrogen removal by modulating DOC release, which subsequently influenced pH, electrical conductivity, and nitrogen transformation pathways. Significant differences among tissues were observed in denitrification efficiency, carbon utilization, and micro-environmental regulation. Mixed tissues and husk emerged as superior carbon sources due to their combined efficiency and stability. However, husk released odorous compounds during operation, posing sensory challenges for practical application. The findings support the potential of corn stover tissues as cost-effective carbon sources for in-situ groundwater nitrate remediation, though further optimization is required for field-scale implementation.