Removal of emerging micropollutants by activated sludge process and membrane bioreactors and the effects of micropollutants on membrane fouling: A review

Recently, emerging contaminants such as micropollutants presence in water poses significant challenge to regulators, engineers and scientific community. Micropollutants are introduced in the aquatic environment primarily from discharge of treated effluent from wastewater treatment plants (WWTP). Advanced treatment processes: reverse osmosis, and membrane bioreactor (MBR) can achieve higher and more consistent micropollutants removal. Despite the used technology, the removal of micropollutants depends on phsyico-chemical properties of micropollutants and the treatment conditions. Several advantages make MBR to be recognized as the next generation for wastewater treatment. However, its efficiency is limited due to the presence of micropollutants, causing peculiar membrane fouling. This review compares MBR and conventional activated sludge (CAS) for wastewater treatment and discusses problems arising from the presence of emerging micropollutants, such as the low removal efficiency for certain types of compounds. Mechanisms of micropollutants removal are summarized and related to MBRs operational conditions based on the vast literature existing in this topic. Adsorption and subsequent biodegradation of the micropollutants have been identified as the dominant removal processes, and they are influenced by operational conditions such as solid retention time, biomass concentration, temperature, redox conditions and pH. The review also provides a detailed overview of the effects of micropollutants on microbial activities, since microorganisms respond to environmental stress by producing different polysaccharides and proteins that have a direct impact on membrane fouling. Finally, pertinent issues that must be addressed in order to increase the market share of MBR in the removal of emerging micropollutants are highlighted.