Micro- and nanoplastics removal mechanisms in wastewater treatment plants: A review

In recent years, the intensification in environmental pollution with micro and nano-plastics (MNPs) has become a global environmental concern. MNPs are some of the emerging contaminants that appear as new challenges to the scientific community because of their adverse effect on human health and environment. Conventional wastewater treatment plants (WWTPs) can efficiently remove the MNPs from the wastewater. The reduction of MNPs from WWTPs has attracted much attention in the past decades. Despite the efficient removal, WWTPs are considered one of the key routes through which MNPs have been introduced to the environment, through the large volumes of effluent continually released to the water bodies. Therefore, a detailed understanding of the behavior of MNPs and their removal mechanisms in WWTPs is highly essential. Nevertheless, an inclusive review of the MNPs treatment techniques in WWTPs is infrequent. So, we review the treatment processes presently employed for MNPs removal in WWTPs to upgrade the existing designs further. In addition, the effectiveness of advanced treatment processes, such as membrane technologies, advanced oxidation process, electro-coagulation, nano technology, etc., in eliminating MNPs are presented and discussed. However, possible toxic microbial biotransformation of MNPs during biological treatment steps in WWTPs needs to be taken care of via further in-depth research. As a basic knowledge of removal mechanisms in WWTPs could reduce the environmental pervasiveness of MNPs, this review is likely to offer helpful information in establishing an efficient approach to control and minimize environmental pollution from MNPs.