The start-up and saline adaptation of mesophilic anaerobic sequencing batch reactor treating sludge from recirculating aquaculture systems

► Digestion and methanogenes occur in ASBR treating sludge from RAS without external carbon source. ► The average daily gas production was between 0.013 and 0.022 L/g TCOD. ► Average removal of TCOD, TSS and VSS were higher than 97%, 96% and 91% during gas production period. ► Gas production stopped when the salinity of the effluents was higher than 8.7 ppt. ► The TSS of the mixed liquor in the ASBR remained stable until day 20 while the salinity was below 4 ppt.