Microplastics removal technologies from aqueous environments: a systematic review.

Purpose: Pollution of the environment with all kinds of plastics has become a growing problem. The problem of microplastics is mainly due to the absorption of stable organic pollutants and metals into them, and as a result, their environmental toxicity increases. The main purpose of this study is to investigate the appropriate and efficient methods of removing microplastics from aqueous environments through a systematic review. Methods: Present study designed according to PRISMA guidelines. Two independent researchers followed all process from search to final analysis, for the relevant studies using international databases of PubMed, Scopus and ISI/WOS (Web of Science), without time limit. The search strategy developed based on the main axis of "microplastics", "aqueous environments" and "removal". This research was carried out from 2017 until the March of 2022. All relevant observational, analytical studies, review articles, and a meta-analysis were included. Results: Through a comprehensive systematic search we found 2974 papers, after running the proses of refining, 80 eligible papers included to the study. According to the results of the review, the methods of removing microplastics from aquatic environments were divided to physical (12), chemical (18), physicochemical (27), biological (12) and integrated (11) methods. In different removal methods, the most dominant group of studied microplastics belonged to the four groups of polyethylene (PE), polystyrene (PS), polypropylene (PP) and polyethylene tetra phthalate (PET). Average removal efficiency of microplastics in different processes in each method was as: physical method (73.76%), chemical method (74.38%), physicochemical method (80.44%), biological method (75.23%) and integrated method (88.63%). The highest removal efficiency occurred in the processes based on the integrated method and the lowest efficiency occurred in the physical method. In total, 80% of the studies were conducted on a laboratory scale, 18.75% on a full scale and 1.25% on a pilot scale. Conclusion: According to the findings; different processes based on physical, chemical, physicochemical, biological and integrated methods are able to remove microplastics with high efficiency from aqueous environments and in order to reduce their hazardous effects on health and environment, these processes can be easily used.