Contribution of planktonic bacteria to MBR fouling

Dissolved extracellular polymeric substances (EPS) are often mentioned as the main foulant in membrane bioreactors (MBR). However, single bacterial cells may be the most important foulant but are often erroneously measured as EPS in traditional spectrophotometric analysis. Raw sludge and sludge supernatant with varying concentrations of planktonic cells was filtered, and showed a direct correlation between the planktonic cell count and rate of flux decline. Thus, high concentrations of single cells result in membrane fouling. DNA fingerprinting of activated sludge samples from a full scale MBR wastewater treatment plants (WWTP) was applied to determine the identity of the most abundant single cells. Several bacteria genera were observed to be enriched in the water phase, many of them known to be abundant in influent wastewater and these may influence fouling propensity in MBR systems.