Extraction and analysis of extracellular polymeric substances in membrane fouling in submerged MBR

The extraction and analysis of EPS in active biomass and membrane fouling were performed to investigate the influence of extracellular polymeric substances (EPS) on membrane fouling of MBR. The new membrane and fouling membrane surface morphology was characterized by EDX analysis. The results show that membrane contaminant is mainly composed of organic compounds. EPS in active biomass and membrane pollutant were extracted by method of alkaline regular centrifugation. Most of EPS were found to have high molecular weight over 12,000 D, which is very difficult to degrade. The total EPS contents in the extracted solution and the contents of polysaccharide protein and DNA in EPS were respectively analysed with TOC analysis and by phenol-sulfuric acid method, modification of the Bradford method and the fluorometric method. The analytical results indicate that the content of EPS in membrane fouling is about four times as much as that in active biomass, and polysaccharide is the most important pollutant on membrane, as well as protein’s role in membrane fouling is not negligible, whereas the DNA is not important in membrane fouling because of its content (non-dialysis) in membrane contaminant being less than that in the active biomass. In addition, the results in electrophoresis experiment provide the information about the concentrated distribution of molecular weight of large fragment DNA in both membrane contaminant and the biomass.

1. The new membrane and fouling membrane surface morphology were characterized by EDX analysis. The results show that the majority of membrane contaminants are organic substances, whereas the proportion of inorganic substances to organic substances in membrane contaminant is very low. 2. The measured TOC value for membrane contaminants is about three times larger than that for the biomass in the mixed liquor. This means that EPS is the main contaminant in membrane fouling. And most of EPS in membrane fouling have a high molecular weight — over 12,000 D— because the differences between the measured polysaccharide, protein and DNA contents before dialysis and after dialysis are small. 3. From the results in EPS analysis, polysaccharide and protein were found to be the main polymers in EPS and the polysaccharide is a key component in membrane fouling because of its high viscosity and its content in EPS from membrane contaminants being 3–4 times larger than that in EPS of biomass in mixed liquor. 4. The proportion of the measured DNA (nondialysis) to EPS from membrane fouling is less than that from the biomass. But DNA attached to membrane surfaces is mainly composed of long sections. The information provided by electrophoresis suggests that the length of large fragments of DNA in both the membrane contaminant and the biomass is focused on about 200–300 bp.