The waste recycling approach for enhancing wastewater sludge dewaterability by using iron-mud (IM)/sawdust derived carbon composite

• Iron-mud (IM) / sawdust derived carbon composite was synthesized and characterized. • IMS composite significantly influence on improving sludge dewatering performance. • A new method is explored to transform the environmental risk into profitable products. The dewaterability of wastewater sludge by the solid waste of iron-mud (IM)/carbon (IMS) composite prepared via the in-situ carbothermal reduction method was systematically studied in this paper. It investigated the effects of different IMS materials, IM dosages and stirring speeds on sludge dewaterability, including water content (WC), capillary suction time (CST), extracellular polymeric substances (EPS) contents and particle size. The results of dewatering tests demonstrated that IMS materials significantly enhanced sludge dewaterability, resulting in a reduction of 39.85 % in CST and 13.26 % reduction in WC in the dewatered sludge under optimum condition (IMS-3 dosage of 8 % dry solids; stirring speed of 250 r/min for 30 min). Electron paramagnetic resonancec (EPR) and scavenging experiments were conducted to better understand the dewatering process mechanism. This results indicated that both hydroxyl radicals (•OH) and superoxide radicals (•O 2 − ) collaborate during the dewatering process. Furthermore, analysis were performed on the particle size of sludge flocs and scanning electron microscopy (SEM) imaging of sludge morphology to reveal the synergistic effects of IMS treatment. A two-step mechanism involving oxidation and Fe(III)-based re-flocculation maybe explain the synergistic effect of IMS treatment. This novel recycle-based IMS composite approach offers a new management strategy for industrial solid wastes while enhancing the sludge dewatering efficiency. Scheme 1 The possible mechanism of sludge dewatering on IMS materials.