In situ and short-time anaerobic digestion coupled with alkalization and mechanical stirring to enhance sludge disintegration for phosphate recovery

•Anaerobic digestion coupled with alkalization and mechanical stirring was studied.•Initial pH pretreatment was effective for disintegration with greater SOP release.•Chemical effects has a more significant role than bacterial ones with pH increase.•Alkalization transformed all NAIP and most of the IP into phosphate in supernatant.