Enhancing methane production and removing long-chain fatty acids via calcium-based granules generation under high-solid anaerobic digestion of kitchen waste

In this study, calcium was added to remove long-chain fatty acids (LCFAs) inhibition and improve biogas yield performance for the anaerobic digestion (AD) of kitchen waste (KW). The granules with diameters of 1-2 mm were observed formation in completely stirred tank reactors. The microstructure and chemical composition of the pellets were analyzed and 10 LCFAs were identified. Three mechanisms of pellet formation in a mesophilic AD were identified: lipid hydrolysis, crystallized nucleus formation, and granule growth. Further, the effect of different ratios of Ca2 + to LCFAs (Ca/LCFAs) on methane production and LCFAs removal efficiency in AD was investigated. The results indicated the maximum total methane production of 212.7 mL center dot g- 1 (VS) was obtained at Ca/LCFAs of 4:1. The appropriate Ca/LCFAs were between 2:1 and 4:1, and the removal efficiency of LCFAs was also improved by increasing the Ca/LCFAs within this optimal range. The formation process of granules in a mesophilic AD was conducted. It is technically applicable to add calcium to obtain optimal Ca/LCFAs for AD of KW, which was of great benefit to alleviating LCFAs inhibition and improving biogas yield simultaneously.