Effects of microplastics on wastewater and sewage sludge treatment and their removal: A review

Microplastics are widely used and inevitably released into the environment, which can be easily enriched in wastewater treatment plants. This review assesses their potential effects on wastewater and sludge treatment and the methods for removing microplastics from wastewater and sludge. Firstly, recent advances of the methods for purification and detection of microplastics in wastewater and sewage sludge environment were reviewed. Then, the effects of microplastics on wastewater and sludge treatment and the mechanisms were discussed. It can be seen that when the size of microplastics reached the nanometer level, they infiltrated into the biofilm and produce ROS, which showed acute inhibitory effect on microbial community, key enzymes, metabolic intermediates and final products. Due to their large specific surface area and hydrophobic surface, persistent organic pollutants, metals and pathogens could be easily adsorbed on the surface of microplastics. As various additives were added in the production of plastics, the adsorption of environmental micropollutants and the exudation of additives made the mechanism of microplastics affecting sewage and sludge treatment more complicated. Also, the methods for removing microplastics from wastewater and sludge were reviewed and their removal efficiencies were compared. Finally, the problems that need to be addressed in the future were pointed out, and the key points for future investigation were proposed.