Vetiver Phytoremediation of Nitrate-Rich Munition Wastewater: Biomass Valorization Within a Circular Economy Framework

Industrial munition facilities generate nitrate-rich wastewater that requires effective and sustainable treatment before discharge. While vetiver grass (Chrysopogon zizanioides)-based phytoremediation has shown promise in nitrogen removal, most studies have been limited to small-scale experiments under low nitrogen concentrations, providing limited guidance for system-level design under elevated loading. This study evaluates a greenhouse-scale phytoremediation system using vetiver grass to treat wastewater containing 1000 mg N/L nitrate and 50 mg/L COD. Plant coverage densities of 2%, 4%, and 6% (w/v) were assessed to quantify optimum density as a design parameter for optimizing nitrate removal. A 6% coverage achieved the highest efficiency, reducing nitrate by 75% to 253 mg N/L over four months. Plant growth, chlorophyll, protein content, and antioxidant enzyme activity were analyzed to elucidate physiological adaptation under sustained nitrate stress. Harvested biomass was subsequently valorized into biochar and bioethanol, with TCLP tests confirming minimal leaching risk. By integrating performance optimization, stress-response analysis, and biomass conversion, this work advances vetiver phytotechnology toward scalable, design-oriented nitrogen removal within a circular treatment framework.