+Efficient dewatering and heavy-metal removal in municipal sewage using oxidants

Municipal sewage sludge (MSS) is widely used in agriculture. In this study, three oxidants (Fenton's reagent, K2S2O8, and CaO2) were used to simultaneously dehydrate MSS and remove heavy metals, and the heavy metals in the supernatant were separated via the addition of CaO. The respective removal rates of Pb, Zn, Cu, and Cd were 56.8%, 84.9%, 88.3%, and 92.3% using Fenton's reagent; 66.9%, 86.1%, 88.9%, and 82.8% using K2S2O8; and 53.0%, 58.3%, 64.8% and 2.1% using CaO2. Thus, Fenton's reagent and K2S2O8 were preferable for heavy metal removal, especially for Cd. The treated sludge was safe for agricultural use based on the standards for pollutants in sludge for agricultural use (GB4284-84). The oxidants also exhibited good dewatering performance for MSS and caused the extracellular polymeric substance (EPS) of MSS to decompose quickly. The water content of the sludge was reduced from 99.08% to 76.1% (Fenton's reagent), 74.7% (K2S2O8), and 66.5% (CaO2). Hence, the treated sludge was easy to transport and could be safely used in agricultural production. After oxidant treatment, CaO was added to the supernatant, allowing the metals in the supernatant to be separated. This method can reduce Wc and heavy metal content of sludge at low cost.