Does fouling in MBRs depend on SMP?

Fouling is still one of the major issues of the membrane bioreactor (MBR) research. Most attention is currently paid to extracellular polymeric substances (EPS) in either bound or soluble/colloidal (soluble microbial products, SMP) form. While several trends or correlations were reported, the comparability of results is still limited by the numerous differences in plant set-up and analytical methods. The aim of this study is to compare polysaccharide concentrations and their respective fouling potentials in different MBRs operated under different conditions using the same analytical and evaluation tools and considering all relevant differences. The results are also compared to the literature findings in an attempt to come to more generally valid conclusions. The results indicate that SMP influence fouling only under certain conditions such as low sludge age and large pore size.

SMP concentrations and fouling rates were determined over several months of operation in three MBR plants of different size equipped with flat sheet ultrafiltration modules and operated under different conditions. In contrast to several literature studies, no correlation between PS concentration and membrane fouling was observed. This was attributed mainly to the fact that literature correlations were found for microfiltration membranes where pores are more susceptible to penetration by PS. The results in the current study which were obtained at rather high SRT (20–30 d) also confirm recent literature indications that as SRT increases, the relevance of SMP for filtration resistance and fouling decreases. The results indicate that SMP influence fouling only under certain conditions such as larger pore size and low sludge age.