Biochar stimulates growth of novel species capable of direct interspecies electron transfer in anaerobic digestion via ethanol-type fermentation

Abstract

The study presented here was to evaluate the effects of combining biological ethanol-type fermentation pretreatment (BEFP) with biochar on the growth of novel species capable of direct interspecies electron transfer (DIET) and methanogenesis in anaerobic co-digestion (AcoD) of kitchen wastes (KWs) and waste activated sludge (WAS). The results showed that, after BEFP, the genera capable of extracellular electron transfer to Fe(III) oxides or the elemental sulfur, such as Geobacter, Sphaerochaeta and Sporanaerobacter species, were detected, which however were not detected in the seed sludge. In the presence of biochar, their abundance was further increased, suggesting that biochar stimulated their growth. With biochar, methane production rate increased by about 44% and the effluent concentration of total organic substrates further declined, compared with that without biochar. With biochar, methane production efficiency reached 241.6 mL/g-COD, more than 30% higher than that without biochar (185.0 mL/g-COD), suggesting that more energy from the oxidation of organic substrates was converted into methane. Analysis of Fourier transform infrared spectroscopy (FT-IR) and three-dimensional excitation emission matrix (3D-EEM) showed that decomposition of complex organic compounds in KWs and WAS was enhanced, since the novel species might proceed DIET with methanogens and participate in the metabolism of complex organic compounds.