Divalent cation chelation enhancing carbon migration and recovery from anaerobic fermentation of waste activated sludge

Recently, the short-chain fatty acids (SCFAs) production with carbon recovery from waste activated sludge has received increasing attention. Despite that numerous approaches have been investigated, the divalent cation chelation towards enhancing anaerobic fermentation and the carbon migration fates has been rarely reported. This work attempted to chelate structural divalent cations from sludge flocs by sodium pyrophosphate (SP) at the dosages of 0-0.6 g/g SS, facilitating sludge disintegration and hydrolysis with particulate organic matters sol-ubilization. At the optimal SP dosage of 0.4 g/g SS, the chemical oxygen demand (COD) and carbon source content in sludge solid were reduced by 45.24 % and 35.50 % within 1-day treatment, leading to considerable sludge hydrolysis and carbon release performances with soluble COD/total COD of 23.21 % and carbon release rate of 26.94 % in 2-day anaerobic fermentation, respectively. Numerous SCFAs of 237.43 mg COD/g VSS were produced by 4-day anaerobic fermentation, with the overall carbon recovery rate of 21.19 %, which were dominantly composed by acetate and propionate. Meanwhile, the SP-inhibited biogas generation also contrib-uted to SCFAs accumulation. The divalent cation chelation obviously improved rate constant and equilibrium performances of anaerobic fermentation process, which were 1.81-5.21 and 1.36-2.82 times higher than those without SP, respectively. The carbon migration pattern was proposed by interphase carbon source balance and the mechanism was also illustrated. The crucial novelty was to propose an innovative and economic sludge hydrolysis pattern by divalent cation chelation towards improving carbon recovery.