Methane production from algae in anaerobic digestion: Role of corncob ash supplementation

The recycling and utilization of waste has attracted increasing attention due to the requirement of sustainable development. This study proposed a novel waste reuse technology using crop incineration waste (i.e., corncob ash) as an additive to enhance the methane production from anaerobic digestion of algae. Biochemical methane production tests demonstrated that corncob ash (0.6, 0.9 and 1.2 g/g TS (Total Solids)) enhanced methane production from algae, and the maximal methane production was 75.8 ± 1.2 ml CH4/g VS (Volatile Solids) achieved at 0.6–0.9 g/g TS of corncob ash addition, representing the relative increase of 35–37% compared to that without corncob ash. By monitoring the transformation of metabolic intermediates, corncob ash was confirmed to be beneficial to the solubilization, hydrolysis and methanogenesis processes during anaerobic algae digestion. This was supported by the microbial analysis results that corncob ash enriched the related key microorganisms, e.g., Longilinea sp. and Methanosaeta sp.. Moreover, mechanism studies revealed that corncob ash alleviated ammonia inhibition and improved the electron transfer efficiency for methane production, which was probably attributed to the porous structure and high redox characteristics of corncob ash. The anaerobic digestion residue with corncob ash rich in inorganic elements (e.g., potassium, calcium and magnesium) could also be used as a potential agricultural fertilizer for soil. The novel strategy proposed in this study might provide a new paradigm of an integrated waste-control by waste to bring significant economic and environmental benefits to waste disposal.