Jointly reducing antibiotic resistance genes and improving methane yield in anaerobic digestion of chicken manure by feedstock microwave pretreatment and activated carbon supplementation

Abstract

Antibiotic resistance genes (ARGs) stemming from animal manure pose adverse impacts on human health and ecology and consequently cost more to treat the anaerobic digestate after manure fermentation. To jointly reduce the ARGs and improve the methane yield during anaerobic digestion (AD) of chicken manure, microwave pretreatment of manure and activated carbon supplementation were simultaneously applied and evaluated in an anaerobic digester (R1). For comparison, three other digesters, a digester (R2) fed with raw chicken manure without activated carbon, a digester (M1) fed with microwave-pretreated chicken manure and without activated carbon, and a digester (M2) fed with raw chicken manure supplemented with activated carbon, were operated in parallel. The results showed that after 47 days of AD operation, R1 achieved an 87–95% ARGs removal rate, significantly higher than that of R2 (34–58%). As the loading rate was 5.8–7.0 g volatile solids (VS)/L, the average methane yield of R1 was 0.287 L/g VS, which was 1.4-fold, 1.3-fold and 1.1-fold higher than that of R2, M1 and M2, respectively. The increased methane yield was ascribed to the combined effect of feedstock microwave pretreatment and activated carbon supplementation. Pyrosequencing analysis showed that the dominant bacterial phyla were Firmicutes, Bacteroidetes and Proteobacteria while the dominant archaeal genus were Methanosarcina, Methanothrix, Methanolinea, Methanomassiliicoccus, Methanospirillum, Methanoregula and Methanobacterium. The KEGG cluster analysis and functional analysis of genome from archaeal communities demonstrated that the dominant functions enhanced by substrate microwave pretreatment and activated carbon supplementation were linked to amino acid metabolism, carbohydrate metabolism, cell communication, energy metabolism, signaling molecules and interaction, and signal transduction.