Impacts of biochar on anaerobic digestion of swine manure: Methanogenesis and antibiotic resistance genes dissemination.

This work aimed to study the effects of biochar on methanogenesis and antibiotic resistance genes (ARGs) fate during anaerobic digestion (AD) of swine manure (SM) was investigated. Under the optimal biochar dosage of 5-10%, methane yield was significantly improved by 25%, ascribing to the enhancement of direct interspecies electron transfer (DIET). Biochar addition alleviated the need of cytochrome-c as interspecies electron connection components and enriched the microbes involved in DIET. Defluviitoga, Thermovirga and Cloacibacillus were dominant with biochar addition and might participate in DIET together with Methanothrix. The abundance of parC, tetX, bla, bla, aac(6')-Ib-cr, ermB and tetW were significantly reduced in biochar treatments and intI1 removal increased by 15% in B-5% than the control. Structural equation models demonstrated that intI1 (λ = 0.59, P < 0.001) had the most standardized direct effects on ARGs, while biochar indirectly affected ARGs by changing intI1 (λ = 0.41, P < 0.01) and microbial structure (λ = -0.24, P < 0.05).