Impact of operational parameters on degradation of nitroglycerin using biochar doped with nano zerovalent iron

Wastewater from munition manufacturing facilities contains nitro compounds amenable to reductive degradation. Nanosized zero-valent iron (nZVI) offers a cost-effective solution but tends to agglomerate, reducing its efficacy. Biochar (BC), a sustainable carbon material derived from organic waste, improves nZVI's performance by dispersing the nanoparticles and providing more active sites. This study explores the influence of reagent synthesis and reaction conditions on a rice hull biochar-supported nZVI (nZVI-RBC) system for removing nitroglycerin (NG) from untreated munitions wastewater. Key parameters examined included biochar pyrolysis temperature, iron-to-biochar ratio (Fe:BC), reagent dosage, and initial pH. The nZVI-RBC system removed over 99 % of NG within 30 minutes under base conditions (Fe:BC=1:1, (Fe:BC=1:1, [nZVI_RBC400]=1 g/L, unadjusted pH), significantly outperforming pristine nZVI, which removed only 57 %. Biochar improved the working pH range of nZVI particles so that nZVI-RBC was efficient over a wide pH range of 3–9; even in extreme alkaline condition (pH 11) it removed 94 % of NG. This remarkable efficacy was observed in an open system, which is especially notable. NG treated with nZVI-RBC underwent a series of sequential reductive cleavage and denitration of the nitro groups. A degradation pathway is proposed with glycerol and ammonium being the major end-products. The reaction predominantly involved surface-mediated reductive degradation. All degradation byproducts were quantified, and carbon and nitrogen mass balances were established. The carbon mass balance was closed within 5 % deviation. Nitrogen mass balance remained partially closed due to the adsorption of ammonium on the surface of biochar and ammonia volatilization.