Sludge lime stabilization supernatant (SLSS) was reused to treat reject water.
High content of calcium and alkalinity in SLSS favors P removal from reject water.
SLSS supplemented alkalinity and carbon for biological N removal from reject water.
SLSS raised sludge flocs, and mitigated fouling of MBR for reject water treatment.
Adding SLSS increased microbial abundance and biodiversity, and enriched nitrifiers.