Comprehensive study of the combined effects of biochar and iron-based conductive materials on alleviating long chain fatty acids inhibition in anaerobic digestion

Abstract

This study investigated the feasibility of alleviating the negative influence of long-chain fatty acids (LCFAs) on anaerobic digestion by biochar, micron zero-valent iron, micron-magnetite (mFe₃O₄) and their combination. The results demonstrate that co-addition of biochar and 6 g/L mFe₃O₄ (BC+6 g/L mFe₃O₄) increased cumulative methane production by 50% as suffered from LCFAs inhibition exerted by 2 g/L glycerol trioleate. The BC+6 g/L mFe₃O₄ did best in accelerating total organic carbon degradation and volatile fatty acids conversion, through successively enriching Bacteroides, Corynebacterium, and DMER64 to dominant the bacterial community. The proportion of acetotrophic Methanothrix that could alternatively reduce CO₂ to methane by accepting electrons via direct interspecies electron transfer (DIET) was 0.09% with BC+6 g/L mFe₃O₄, nine times more than the proportion in control. Prediction of functional genes revealed the enrichment of the bacterial secretion system, indicating that BC+6 g/L mFe₃O₄ promoted DIET by stimulating the secretion of extracellular polymeric substances. This study provided novel insights into combining biochar and iron-based conductive materials to enhance AD performance under LCFAs inhibition.

Keywords: Anaerobic digestion; Biochar; Direct interspecies electron transfer; Long-chain fatty acids; Micron zero valent iron; Micron-magnetite.