Rapid nitroglycerin removal using nZVI-biochar: A comprehensive investigation on treatment fate, byproduct kinetics, reaction pathway modeling and statistical optimization

Rice hull biochar doped with zerovalent iron nanoparticles (nZVI-RBC) has been used for the degradation of various contaminants; however, there is limited information available on the treatment of nitroglycerin (NG), a compound found in untreated wastewater from pharmaceutical and munition industries. This study used an integrated approach combining empirical data and modelling to determine: 1) experimental results, 2) reaction kinetics modelling, and 3) statistically based treatment optimization. The impact of various operational and synthesis parameters on treatment was determined experimentally, and kinetic modelling was employed to provide insights into the underlying degradation reactions and mechanisms. nZVI-RBC treatment applied to NG resulted in carbon mass balance closure of 95–99%. The byproducts were identified and indicated reductive degradation via denitration to benign glycerol as the end-product. More than 96% of NG removal was observed within 30 min of reaction time in most conditions. nZVI-RBC was effective in degrading NG in a wide range pH range of 3–9. The kinetic models developed consisted of two degradation pathways: 1) sequential denitration, and 2) concurrent denitration (i.e. bypassing intermediate byproduct formation). Kinetic modeling indicated that degradation via concurrent denitration directly to glycerol was more prevalent. Treatment optimization was studied to determine the statistically significant factors; a multilinear regression (MLR) model was developed and correlation coefficients were determined for iron %, biochar content, initial pH and pyrolysis temperature. The MLR model also suggested that enhancing the NG degradation rate will likely contribute to byproduct accumulation in the system.