Influence of sludge retention time at constant food to microorganisms ratio on membrane bioreactor performances under stable and unstable state conditions

► Effect of SRT (20 and 50 d) at constant F/M ratio on MBR performances was assessed. ► Autotrophs and heterotrophs showed higher exogenous activities at SRT of 50 d. ► Higher soluble microbial products (SMP) release was observed at SRT of 50 d. ► SMP were composed at 49% of polysaccharides at SRT of 50 d.