Characteristics and effects of extracellular polymeric substances and soluble microbial products in membrane bioreactor

Abstract

In recent years, however, stricter environmental legislation and the growing costs of wastewater treatment have increased the attractiveness of the high and reliable degree of purification that can be achieved with membrane bioreactor. However, the problem of membrane fouling is as old as membrane filtration itself. In this study, the phenomenon of membrane fouling was extensively studied at various microbial conditions, influent conditions, airflow rates, sludge retention times and soluble organic concentrations. Moreover, the pilot-scale membrane bioreactors were operated to prove the results obtained from lab-scale reactor. The role of extracellular polymers on microbial surface characteristics and on adhesion of microorganisms to membrane surface was investigated on chapter 3. The surface charge was linearly increased with the increase of carbohydrate to protein ratio in the EPS (EPSc/EPSp), which weaken the bonding force between microorganisms and multivalent cations. Higher negative surface charge of microorganisms also induced the easy adhesion to the membrane surface which was negatively-charged and hydrophilic. As the result, the portion of cake resistance to total resistance increased with the increase of negative charge of membrane surface. The ratio of EPSc/EPSp could be used as the indicator of potential biofilm formation on the membrane surface. The investigation of characteristics of microorganisms and their soluble microbial products (SMP) at various influent conditions showed that the sludge concentration was proportional to the organic concentration of the influent and sludge retention times (SRT). On the other hand, total amount of EPS and the composition of EPS were not so much different at different influent conditions. The concentration of soluble microbial products (SMP) was similar despite of influent COD concentration, however, the hydrophobicity or specific UV absorbance was inversely proportional to the influent COD concentrat...