Heavy metals migration and antibiotics removal in anaerobic digestion of swine manure with biochar addition

Abstract

Anaerobic digestion (AD) is a key technology for the utilization of swine manure, but the complex pollution of heavy metals and antibiotics in manure is catching more attentions. In this study, AD of swine manure loading with four types of biochar was performed in a 1 L-frosted jar with the total fresh weight of 840 g, in which the effects of biochar on the AD stability and methane yields were focused, and the removal of antibiotics and migration of heavy metals were investigated as well. The results showed that the removal efficiencies of sulfadimidine and tylosin were remarkable, which were up to around 70% and 100%, respectively. The maximum methane yield of 146.98 mL/ (g VS) was noted in the digester added with the biochar derived from paper mill sludge (BPMS) which contained 87.35% of ash, having a high pH PZC of 8.95 and more mesopores and macropores. In this reactor, 12.40% of Cu was moved to the solid phase, and 70.26% of Zn and 82.80% of As were migrated to the solid digestate. Compared to the control, the content of the acid soluble Cu in the digester loaded with BPMS was decreased to 7.99%, and no acid soluble Zn was found along with a drop of 29.20% for the reducible Zn, and the residual As content was increased by 16.60%. It revealed that BPMS had a great potentiality to remove As and Zn in wastewater and synchronously mitigate the bioavailability of Cu/Zn/As in the digestate. Herein, applying BPMS in the AD of swine manure could reduce the complex pollution of heavy metals and antibiotics, and obtain a higher methane yield simultaneously. • Paper mill sludge biochar had high pH PZC and was rich of ash, macropores and mesopores. • Around 70% of SDM and 100% of TYL were degraded in AD. • Highest methane yield was noted in the digester loaded with paper mill sludge biochar. • 70.26% Zn and 82.80% As migrated to solid digestate via paper mill sludge biochar adsorption. • Paper mill sludge biochar could reduce the eco-toxicity of Cu, Zn, As in the digestate.