Study of the extracellular polymeric substances (EPS) in different types of membrane bioreactor (MBR) effluents

One of the problems involved in operating membrane bioreactors (MBR) is membrane fouling. This is caused by the presence of wastewater constituents such as colloids, mineral particles, ionic components, micro-organisms and basically because of extracellular polymeric substances (EPS). EPS are high-molecular weight compounds secreted by microorganisms into their environment, and they are mostly composed of proteins and polysaccharides. An exhaustive study of EPS concentration is essential to improve MBR operation. In this paper, a comparative study of the most frequently used EPS extraction methods has been done: extraction using a cation exchange resin (CER) (Dowex 50X8), using formaldehyde (36.5%) + NaOH 1M and by heating. The best results were obtained when the CER was used, extracting in almost all experiments more than double the EPS extracted by the other two techniques. Additionally, determination of the optimum amount of CER required was carried out. The obtained value was 70 g CER/g VS. Afterwards, EPS determination of four different types of effluent using the same method was carried out. The wastewaters used were the following: a) young age sludge coming from an ice cream factory; mixed liquor from the municipal wastewater plant "Rincon de Leon", Alicante; mixed liquor obtained from the pilot membrane bioreactor of "Rincon de Leon", Alicante; mixed liquor obtained from a full scale MBR plant.