Stepwise alkaline treatment coupled with ammonia stripping to enhance short-chain fatty acids production from waste activated sludge

To recover resource from waste activated sludge (WAS) is of great significance. This study proposed a promising way, i.e., stepwise alkaline treatment coupled with ammonia stripping, to remarkably enhance short-chain fatty acids (SCFAs) production from WAS anaerobic digestion. The maximal production of SCFAs, with the value of 323 mg COD/g volatile suspended solid, was obtained with first initial pH = 10 adjustment followed by second initial pH = 10 adjustment on third day coupled with ammonia stripping. Mechanistic studies showed that solubilization of both extracellular polymeric substances and cells could be accelerated by stepwise initial pH = 10 adjustment. However, without ammonia stripping, the activities of either acidogens or methanogens could be inhibited by free ammonia formed under alkaline conditions; positively, anaerobes related to SCFAs production were enriched with ammonia stripping. Moreover, the proposed strategy can simultaneously achieve nitrogen and carbon recovery, providing some solutions for the carbon–neutral operation of wastewater treatment plants.