Influence of hydraulic retention time on the nature of foulant organics in a high rate membrane bioreactor

► A change of HRT of an MBR alters the biomass characteristics and fouling propensity. ► Shorter HRT led to rapid rise in TMP due to sludge addition and biopolymer formation. ► A longer HRT favoured more biopolymer in the foulant on the membrane surface. ► A shorter HRT favoured more humics in the foulant. ► UV spectra can be used as an initial tool to monitor the fouling that occurs.