The effects of biocarriers on the mixed liquor characteristics, extracellular polymeric substances, and fouling rates of a hybrid membrane bioreactor

In this research, the influence of biocarriers on the mixed liquor characteristics, extracellular polymeric substances (EPS), and fouling rates of a hybrid membrane bioreactor (HMBR) were examined during greywater reclamation. The addition of the biocarriers increased the relative abundance of filamentous bacteria within the HMBR, which decreased the settleability of the sludge, but did not affect its dewaterability or filterability. Settleability was found to be strongly correlated to the biocarrier filling ratio (R2 = 9.0). The biocarriers appeared to have no effect on the total concentration or protein-to-polysaccharide (PN/PS) ratio of the mixed liquor EPS. However, an analysis of the fouled membranes revealed that the PN/PS ratio of the cake layer EPS was significantly reduced in the presence of the biocarriers. It was also found that the biocarriers reduced the fouling rate of the HMBR and extended its operating time by up to 40% (or 11 days). This rate reduction could not be attributed to any mechanical scouring mechanism, since the biocarriers were prevented from contacting the membrane module during operation.