A Comprehensive Investigation of the Factors Affecting the Treatment of Trinitrotoluene Redwater by Coagulation and Electro-Fenton

Redwater is a highly toxic waste generated during the purification of 2,4,6-trinitrotoluene (TNT), one of the most widely used military explosives. Redwater treatment is difficult because of its high chemical oxygen demand (COD) and strong red color. In this study, we present a comprehensive study on the treatment of the actual TNT redwater by a combination of chemical coagulation and electro-Fenton process. The pretreatment by traditional coagulation using poly-aluminum chloride (PAC) was investigated at different operation conditions of solution pH (4–11), PAC concentration (500–3500 mg/L), flocculant concentration (0–3.5 mg/L), times for coagulation (0–7 min) and flocculation (0–4 min), and stirring speed (100–700 rpm). This pretreatment could removal 52.84% of COD, 53.22% of color, 36.76% of TSS, and 25.88% of total nitrogen under optimal conditions (i.e., pH 7.0, PAC dosage of 2500 mg/L, anion flocculant dosage of 1.25 mg/L, coagulation time of 4 min, flocculation time of 1 min, and stirring speed of 500 rpm). The pretreated redwater was then subjected to an electro-Fenton process using Pt/Ti as anode and carbon felt as the cathode. The effects of solution pH (2–6), iron content (0.05–1 mM), current intensity (8.33–33.33 mA/cm 2 ) and reaction times (0–200 min) on the electro-Fenton treatment were investigated. Under optimal condition (i.e., pH 3.0, Fe(II) concentration of 0.1 mM, current intensity of 16.67 mA/cm 2 , and reaction time of 120 min), the removal efficiency reached 87.07, 96.2, 72.94, and 50.26% for COD, color, TSS, and total nitrogen, respectively. UV-Vis spectroscopy results confirmed the role of electro-Fenton for the effective removal of aromatic nitro compounds in the redwater. These results suggest that the combination of coagulation and electro-Fenton process could be a promising technology for treating TNT redwater.