Insight into Na+ assistant anaerobic fermentation of waste activated sludge from carbon migration, bio-transformation and recovery perspectives

Abstract

Short-chain fatty acids (SCFAs) produced from anaerobic fermentation of waste activated sludge (WAS) have been regarded as the preferred carbon source, however the carbon migration pattern has rarely been reported. This work elucidated that the Na+ assistant anaerobic fermentation could facilitate carbon source release and bio-transformation towards carbon recovery from WAS. Obvious disintegration of sludge flocs and property variation of solid–liquid interface were triggered with Na+-regulation, leading to extracellular polymeric substance disruption and microbial cell apoptosis by protein structure loosening and osmotic pressure stress. Thereby, extracellular and intracellular carbon source (e.g. proteins, carbohydrates) were simultaneously solubilized, contributing to considerable carbon migration from sludge solid into liquid phase (up to 20.43 %). Meanwhile, 61.30 % of the released carbon source was bio-transformed with the improved sludge acidification in 4-day Na+ assistant anaerobic fermentation. Substantial SCFAs of 61.39 mg C/g VSS was produced, which was mainly composed by acetate and propionate (69.07 %). As such, the overall carbon recovery rate of 12.51 % was achievable. The carbon source bio-availability in fermentative liquid indeed created economic benefits and carbon-emission reduction depending on alternative carbon source utilization and residual carbon source reduction in fermented sludge disposal.