Steel slag as accelerant in anaerobic digestion for nonhazardous treatment and digestate fertilizer utilization

[Display omitted] •Steel slags were firstly used as accelerants in the AD system.•Digestate with steel slag accelerants showed potential application as fertilizer.•Improved performance of AD due to the multi-elements released from steel slag.•Resource utilization and nonhazardous treatment of waste were achieved. Accelerants can effectively enhance the performance of anaerobic digestion (AD) system. The effects of optimized steel slag as accelerant in the AD of cow manure and the fertility utilization of the digestate were investigated. Results show that all steel slags collected from different iron and steel companies (slag-1, slag-2, and slag-3) positively affect AD performance in terms of enhancing the biogas yield, methane yield, and chemical oxygen demand (COD) degradation rate. The cumulative biogas yield, methane yield, and COD degradation rate of slag-2 are 507.29 mL/g VS, 274.70 mL/g VS, and 58.62%, respectively. Thermal analysis reveals that the digestate with steel slag has excellent thermal stability and potential application as a component of nitrogen, phosphorus, and potassium organic compound fertilizers. The use of different steel slags as accelerants in the AD system provides a safe and economical avenue to realize the resource utilization and harmless treatment of waste resource.