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  1. Journal of Environmental Health Science and Engineering https://doi.org/10.1007/s40201-023-00872-z RESEARCH ARTICLE Microplastics removal technologies from aqueous environments: a systematic review Arman Arbabi1 · Mitra Gholami1,2  · Mahdi Farzadkia1,2 · Shirin Djalalinia3,4 Received: 5 March 2023 / Accepted: 4 July 2023 © The Author(s), under exclusive licence to Tehran University of Medical Sciences 2023 Abstract Purpose Pollution of the environment with all kinds of plastics has become a growing problem. The problem of microplas- tics 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 micro- plastics 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 Sci- ence), 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 stud- ies, 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) meth- ods. In different removal methods, the most dominant group of studied microplastics belonged to the four groups of poly- ethylene (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%), physi- cochemical 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. Keywords Microplastic · Nanoplastic · Microplastic removal methods · Aqueous environment 2 Mitra Gholami gholamim@iums.ac.ir; gholamimitra32@gmail.com Research Center for Environmental Health Technology, Iran University of Medical Sciences, Tehran, Iran 3 Shirin Djalalinia shdjalalinia@gmail.com Development of Research and Technology center, Deputy of Research and Technology Ministry of Health and Medical Education, Tehran, Iran 1 Department of Environmental Health Engineering, School of Public Health, Iran University of Medical Sciences, Tehran, Iran 4 Non-Communicable Diseases Research Center, Endocrinology and Metabolism Population Sciences Institute, Tehran University of Medical Sciences, Tehran, Iran 1 3

  2. Journal of Environmental Health Science and Engineering Introduction treatment with new filtration methods such as: ultrafiltration (UF), membrane (MBR), reverse osmosis (RO) and carbon filters can separate these harmful substances from drinking water, effectively [12]. With respect to investigations on various methods show the application of a wide range of different physical, chemi- cal and biological processes to remove microplastics from aqueous environments, which are mainly carried out on a laboratory and full scales. Due to different harmful effects of MPs on the human health and environment such as; envi- ronmental toxicity, long shelf life and bioaccumulation of microplastics in nature, and public concern due to their adverse effects on aquatic organisms and may be carriers for many pathogens and sorbents for many toxic, the main purpose of this study is to investigate various appropriate and efficient methods of removing microplastics from aque- ous environments through a systematic review. Recently, microplastics (MPs) have become a controversial issue, mainly due to the adsorption of persistent organic pollutants and metals to them, and as a result, their envi- ronmental toxicity is intensified [1]. In fact, plastic waste is currently considered as one of the biggest environmen- tal problems because millions of tons of plastic are pro- duced annually in the world and many of the plastic wastes that pollute the aquatic environment are microplastics [2]. Microplastics are small plastic parts, fibers and granules that are defined in different sizes with a diameter less than 5 millimeters [3]. The main concern about these particles is related to their ability to collect large amounts of two patho- genic substances called PCBs and PAHs and adsorption of these substances by the tissues of the digestive system. Due to the long shelf life and bioaccumulation of microplas- tics in nature, the World Health Organization has classified these particles as emerging pollutants [4]. Today, there are two main categories for microplastics, which are defined as primary and secondary microplastics. The first category is plastic pieces or particles that are less than 5 mm in size before entering the environment, such as microfibers from clothes, small grains, and plastic tablets. When larger pieces of plastic materials enter the environment through natural weather changes, they are affected by the sun’s UV rays and physical factors, etc., after which physical, mechanical, photolytic or biological decomposition occurs, so they cre- ate the secondary type of microplastics [3, 5]. The wide- spread presence of MPs in various water bodies, for example oceans and urban waters (lakes, rivers, sewage and drinking water), has caused scientific and public concern due to their adverse effects on aquatic organisms [6]. Many effects of plastic waste have been reported on the marine environ- ment. Every year, 5800 artificial waste particles are swal- lowed by each person, most of which comes from tap water. Both micro- and nanoplastics (NPs) may have severe con- sequences of chronic toxicity in aquatic life; However, due to their ability to penetrate the membranes of living organ- isms, NPs may be carriers for many pathogens and sorbents for many toxic [7, 8] and hydrophobic organic pollutants such as heavy metals, pesticides, polychlorinated biphenyls, polyaromatic hydrocarbons due to their high level and have more threat potential [9–11]. Review of previous studies show that in general, different methods have been used to remove microplastics from water sources. In recent years, many researches have been conducted all over the world to remove microplastics from ocean water, replace microbeads with natural materials and use less plastic materials, but there is still little information about the removal of micro- plastics from drinking water. However, considering that the size of these particles is between 1 and 5 microns, water Materials and methods This study is a systematic review that examines “methods for removing microplastics in aqueous environments”. In this research, a comprehensive and complete search of sci- entific documents published in PubMed, Scopus and ISI/ WOS (Web of Science) databases was conducted. The main criteria are based on the words “microplastics”, “aqueous environments” and “removal”, and all related keywords are based on these three axes were considered. The strategy of searching articles according to the keywords selected in this research, is depicted in Table 1. Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) strat- egy was used in this study. The PRISMA statement was published in 2009 to improve the quality of systematic review and meta-analysis reports [13]. PRISMA strategy consists of four stages including identification, screening, eligibility and inclusion. in the first step, the articles related to the subject are identified in the relevant databases. In the second stage (screening), articles that are not related to the topic in terms of the title and abstract are removed from the study. In the third stage (eligibility), articles are carefully examined from the point of view of content, and articles that are not related to the subject in terms of materials, methods, and results are discarded. And finally, in the last stage (Included), the articles that do not match the subject in terms of data extraction and compliance with the qualita- tive evaluation criteria will be removed and the remaining articles will be chosen as selected articles. The keywords used in this search were combined with the medical subject indexes (Mesh) and with the abstract and title. To retrieve all related articles, searching in databases was combined with selected keywords and their synonyms by “AND” and 1 3

  3. Journal of Environmental Health Science and Engineering Table 1 The strategy of searching articles according to the keywords selected in this research Pubmed ((((((“MPs“[Abstract]) OR Nanoplastic*[Abstract]) OR Plastic*[Abstract]) OR Microplastics [MeSH Major Topic])) AND (((“aquatic environment“[Abstract]) OR “Aque- ous Environment“[Abstract]) OR water[Abstract])) AND ((((Removal[Abstract]) OR Elimination[Abstract]) OR Degradation[Abstract]) OR treatment[Abstract]) Scopus ( ( ( TITLE-ABS-KEY ( microplastic* ) OR TITLE- ABS-KEY ( “MPs” ) OR TITLE-ABS-KEY ( nanoplas- tic* ) ) ) AND ( ( TITLE-ABS-KEY ( “aquatic environment” ) OR TITLE-ABS-KEY ( “Aqueous Environments” ) OR TITLE-ABS-KEY ( water ) ) ) ) AND ( ( TITLE-ABS- KEY ( removal ) OR TITLE-ABS-KEY ( elimination ) OR TITLE-ABS-KEY ( degradation ) OR TITLE-ABS-KEY ( treat- ment ) ) ) AND ( EXCLUDE ( SUBJAREA , “COMP” ) OR EXCLUDE ( SUBJAREA , “DENT” ) OR EXCLUDE ( SUB- JAREA , “NEUR” ) OR EXCLUDE ( SUB- JAREA , “NURS” ) OR EXCLUDE ( SUBJAREA , “ARTS” ) ) ISI/WOS TOPIC: (Microplastic*) OR TS=(“MPs”) OR TS=(Nanoplastic*) Indexes = SCI-EXPANDED, SSCI, A&HCI, CPCI-S, CPCI-SSH, BKCI-S, BKCI-SSH, ESCI Timespan = All years TOPIC: (“aquatic environment”) OR TOPIC: (“Aqueous Environ- ments”) OR TOPIC: (water) Indexes = SCI-EXPANDED, SSCI, A&HCI, CPCI-S, CPCI-SSH, BKCI-S, BKCI-SSH, ESCI Timespan = All years TOPIC: (Removal) OR TOPIC: (Elimination) OR TOPIC: (Degra- dation) OR TOPIC: (treatment) Indexes = SCI-EXPANDED, SSCI, A&HCI, CPCI-S, CPCI-SSH, BKCI-S, BKCI-SSH, ESCI Timespan = All years Indexes = SCI-EXPANDED, SSCI, CPCI-S, CPCI-SSH Times- pan = All years methods (e.g., integrated method). Then the results were written in the respective tables and according to the divided methods. In these tables, the information extracted from the studies were divided into columns including: the purpose of the study, the name of the first author and the year of publication, the name of the country, the model and design of the study, the type of microplastic, the treatment method, the removal efficiency, the summary of the study and the points obtained. Results and discussion The review of the studies conducted on the methods and processes of removing microplastics from aqueous envi- ronments shows that different physical, chemical, physi- cochemical, biological and integrated methods have been used to remove them. Among the important and major pro- cesses used in removing microplastics from aqueous envi- ronments, can be mentioned to physicochemical processes like, filtration [12, 15–17], adsorption [18, 19, 8], adsorp- tion with biochar [9, 20] and flotation with dissolved air [21], chemical coagulation [9, 22–30], electrocatalysis, car- bon nanotubes [7], electrocoagulation [31], application of radiation [32, 33], electro-oxidation [34]; coagulation and filtration [4, 10, 35, 36], adsorption and thermal degrada- tion [37], coagulation and flocculation [4, 38], coagulation and sedimentation [39], precipitation [40], photo-catalysts [41–45], centrifuge [46], flotation [1, 47, 48], coagulation and clarification [49] and carbon nanotubes [50]; Biological methods include activated sludge [51–53], use of fungi [5, 54], microbial consortium [55], microalgae [56], sea shells [57, 58], biofilm [59], Biofilter [60], and wetlands [61, 62] and integrated processes such as water and wastewater treatment plants [63–66]. First, an advanced search was performed from the three databases mentioned above and according to the truth table designed based on valid keywords, and a total of 4157 arti- cles were found. All found articles were entered in EndNote software. After first stage removal of duplicate studies in the EndNote software, the number of articles decreased to 2974. Then, the number of articles was reduced to 2436 in the second stage removal of duplicate studies in EndNote. In the next step, unrelated articles were screened according to the available titles and reduced to 212 according to the related titles. At the stage of review of abstracts, the number of selected articles for full text review reached 93 articles. Then, in the review of complete articles, the number of selected articles by checking the desired references, finally reached 80, which were selected as the selected articles of the present study. The steps of selection and screening of articles are given in Fig. 1 by PRISMA method. “OR” operators. In order to increase the sensitivity in the search, the operator “OR” was used between synonyms of keywords. Therefore, for this reason, more articles were found in the initial search from the selected databases, which at first glance, some of them had duplicate and unrelated titles. In the next step, in order to increase the specificity or to make the searched titles specific, all the titles were care- fully checked twice from the point of view of repetition and relevance. At this stage, many articles that were not related to the research topic were removed from the list of searched sources, and only articles with related titles (methods for removing microplastics from aqueous environments) were selected for the next stage (abstract review). In this study, in order to determine the inclusion and exclusion criteria of various experimental studies in screening the full text of articles, the scoring method proposed by Cho et al. and Tim- mer et al. was used as a model for qualitative evaluation of quantitative studies [14]. As mentioned in the introduction section, in this research, the methods of removing microplastics in aqueous environ- ments are divided into four main methods; physical, chemi- cal, physicochemical, biological and a combination of these 1 3

  4. Journal of Environmental Health Science and Engineering Fig. 1 Flowchart of selection and screening of selected articles in this study (PRISMA Flowchart) The number of articles and types of methods for remov- ing microplastics from the aqueous environment in this study are given in an overview in different years in Table 2; Fig. 2, respectively. By examining the available studies in this research, the main microplastics removed in differ- ent removal methods with the processes used were in four groups: polyethylene (PE), polystyrene (PS), polypropyl- ene (PP), and polyethylene tetraphthalate (PET) (Table 3). Average removal percentages of different MPs from aque- ous environment in different removal methods is shown in Fig. 3. The purpose of this systematic review study was to investigate various methods of removing microplastics from aqueous environments. From the point of view of the scale of the studies conducted in this research, it shows that 64 of the studies are on a laboratory scale (80%), 15 are on a full scale (18.75%) and one is on a pilot scale (1.25%). Among the 80 selected articles during frame times from 2017 to 2022, 15% of articles were assigned to the physical, 22.5% to the chemical, 33.75% to the physicochemical, 15% to the biological, and 13.75% to the integrated methods. There- fore, it can be concluded that, on the one hand, research on the methods of removing microplastics is new and has accelerated in recent years due to their health importance (e.g., 2.5% in 2017, 3.75% in 2018, 12.5% in 2019, 30% in 2020, 47.5% in 2021 and 3.75% in 2022). It should be noted 1 3

  5. Journal of Environmental Health Science and Engineering Table 2 The number of articles according to the types of methods for removing microplastics from the aqueous environment in the present study No. Removal Method Removal process Major microplastic Year of publication 2020–2022 Country Number of articles 12 1 Physical Adsorption, filtration, flotation with dissolved air Polystyrene, polyethylene, polyamide India, China, Spain, Indonesia, Switzerland, Finland, Taiwan China, Australia, South Korea, Switzerland, Sweden, America, Canada China, Sweden, Amer- ica, Canada, Malaysia, India, Mexico, Ger- many, Spain, Iran China, South Korea, Canada, Iceland, Denmark, Italy, Saudi Arabia China, South Korea, Finland, Italy, Spain, Belgium, Turkey 2 Chemical Coagulation, electrocatalysis, elec- trooxidation, nanocarbon, UV Polystyrene, polyethylene, polypropylene, polyvinyl chloride 2018–2022 18 3 Physico-chemical Coagulation and filtration, adsorp- tion and thermal degradation, photocatalyst, magnetic carbon nanotubes Biological Using fungi, bacterial consortium, microalgae, biofilter, biofilm Polystyrene, polyethylene, polypropylene, polyvinyl chloride, polyamide 2019–2021 27 4 Polystyrene, polyethylene, polypropylene, polyvinyl chloride, polyamide, poly- ethylene tetraphthalate Polystyrene, polyethylene, polypropylene, polyvinyl chloride, polyamide, poly- ethylene tetraphthalate 2017–2021 12 5 Integrated biological membrane (MBR), Rapid sand filter (RSF), oxidation channel system and rapid sand fil- ter (RSF), oxidation channel (OD) and membrane bioreactor (MBR), A2/O, secondary sedimentation, denitrification, UF, O3, UV 2017–2021 11 Fig. 2 Number of selected articles in different years according to different removal methods Comparing the removal efficiency of various types of microplastics from the aqueous environment that the low number of articles in 2022 is due to the comple- tion of the search by the end of March 2022. On the other hand, the methods used are diverse and include physical, chemical, physicochemical, biological and integrated meth- ods with different processes (Table 2; Fig. 3). According to the studies conducted in this research, among the various studied microplastics (including: polyethylene, polystyrene, polypropylene and polyethylene tetra phthal- ate, microfibers, polyamines, polyvinyl chlorides, poly- methyl methacrylate, cellulose acetate) in different methods 1 3

  6. Journal of Environmental Health Science and Engineering Table 3 Comparison of the removal methods of polyethylene, polysty- rene, polypropylene and polyethylene terephthalate microplastics in different removal processes Removal Method Removal process of removal, the most dominant group of removed micro- plastics belonged into four groups: polyethylene, polysty- rene, polypropylene and polyethylene tetraphthalates. In the methods used to remove polyethylene microplas- tic, the removal efficiency of integrated, physical, physi- cochemical, chemical, and biological methods were 90%, 82.5%, 81%, 72%, and 69%, respectively. In the study that was done by Kim and Park (2020) for the advanced removal of polyethylene microplastics from wastewater using elec- trocoagulation and granular activated carbon with thermal regeneration; Granular activated carbon (GAC) has been able to remove more than 92% of all polyethylene particles in the influent. On the other hand, electrocoagulation was able to increase the removal efficiency in 30 min after coag- ulation. The results of this study show the good efficiency of the integrated method in removing polyethylene micro- plastics [67]. In the methods used to remove polystyrene microplastic, the removal efficiency of integrated, biological, physical, physicochemical and chemical methods were 90%, 85.5%, 75%, 74.5%, and 72%, respectively. The study conducted by Wang et al. (2021) for the removal of polyethylene and polystyrene microplastics using lagoons constructed with vertical flow showed that this process as an integrated method was succeeded in removing polyethylene micro- plastics with the efficiency 98% [68]. In the methods used to remove polyethylene tetraphthal- ate microplastic, the removal efficiency of physicochemical, integrated, physical, chemical, and biological methods were 99%, 97%, 80%, 74%, and 45%, respectively. In a study by Hamzah et al. (2021) for the removal of polyethylene tetra phthalate microplastics using ferrofluid function; this method is considered as a physico-chemical method with an efficiency of over 99%, a high efficiency process to remove this microplastic [69]. In the methods used to remove polypropylene microplas- tics, the removal efficiency of physicochemical, integrated, biological and chemical methods were 93%, 90%, 85.5% and 77%, respectively. In a study conducted by Sturm et al. (2021) for the removal of polypropylene microplastics, it was shown that the new method of organosilanes has a great potential to remove this microplastic on a technical scale, and the chemical composition and surface chemistry of microplastics have a great impact on removal and physi- cal interaction with organosilanes process [70]. Therefore, this process as a physicochemical method has been highly effective in removing this microplastic. Removal efficiency (%) PE PS NA 81 96 90 NA 54 PP NA NA NA PET 100 NA NA Physical Adsorption Filteration Adsorption using biochar flotation with dissolved air Coagulation Electrocoagulation Electrooxidaition VU radiation of zinc oxide nanotubes 69 NA NA 61 Chemical 64 82 NA NA 85 NA 60 NA NA 90 NA NA 74 - NA NA Physico-chemical Coagulation and 57 NA NA NA filtration Coagulation and sedimentation Coagulation and flotation Coagulation and floc- culation and sedimenta- tion and filtration Adsorption and thermal degradation Photocatalytic Thermophotocatalytic Afran coagulating gas Magnetic carbon nanotubes Organosyls Laser beam and sunlight Ferrofluid Nano ferrofluid Activated sludge process Zalerion maritimum mushroom Wetland Shell Membrane biological reactor Rapid sand filter (RSF) Extended activated sludge Oxidation ditch and RSF Wetland with vertical flow Adsorption and electrocoagulation A2/O, secondary sedi- mentation, denitrifica- tion, UF, O3, UV NA 80 NA NA 89 NA NA NA 90 90 NA NA NA 97 NA NA 83 NA NA 100 NA NA 94 NA NA 89 NA NA NA NA NA NA 97 NA 58 54 97 NA NA NA NA 49 98 NA 49 NA NA NA 98 99 NA 17 Biological 43 NA NA NA NA 66 86 73 NA 84 73 NA 86 73 NA 98 Integrated 75 90 75 NA 75 90 NA NA 97 97 97 97 98 98 98 NA 92 NA 92 NA NA 95 95 95 PE: Polyethylene; PS: Polystyrene; PP: Polypropylene; PET: Polyeth- ylene terephthalate; NA: Not available 1 3

  7. Journal of Environmental Health Science and Engineering Fig. 3 Removal percentages of different MPs from aqueous environment in different removal methods Comparing the removal of microplastics from the aqueous environment based on removal methods and conventional activated sludge with screening and grit removal, rapid sand filter and disc filters, respectively. By calculating the removal efficiency of microplastics in each of the physical, chemical, physicochemical, biologi- cal and integrated methods for different and major groups of microplastics, the removal efficiency in the integrated, physicochemical, physical, biological and chemical, meth- ods were 88.63%, 80.44%, 76.73%, 74.38%, 75.23%, respectively;that the highest efficiency of removing micro- plastics occurred in the processes based on the integrated method and the lowest efficiency occurred in the physical method. In a study conducted by Olmos et al. in Spain in 2019, the effectiveness of combined processes for removing low- density and high-density polyethylene, polypropylene, and nylon were investigated. These processes were a combina- tion of extended aeration activated sludge process (ASP), rapid sand filter (RSF) and membrane bioreactor (MBR). The reduction of microplastics from primary effluent to final effluent was 90.2% for ASP, 93.8% for RSF, and 96.2% for MBR, respectively [71]. In a study conducted by Yang et al. in 2019 under the title “removal of microplastics in urban wastewater from China’s largest water treatment plant”, the most common microplastics of polyethylene tetra phthalate, polystyrene and polypropylene were removed by the A2/O process, secondary sedimentation, denitrification, UF, O3, UV with an efficiency of over 95% [66]. These two studies show two types of studies of integrated methods with the highest efficiency in removing microplastics from the aque- ous environment. Examining the performance of different processes in removing different types of microplastics from aqueous environments shows the different efficiency of these pro- cesses in removing these pollutants. For example, in the In comparison of the removal efficiency of the processes based on physical methods, the filtration, the adsorption, the adsorption with biochar, and the flotation with dissolved air have the highest removal efficiency of a set of domi- nant microplastics, respectively. In the processes based on chemical methods, the highest removal efficiency were electrocoagulation, coagulation, electrocatalysis, zinc oxide nanotubes visible light irradiation process, electrooxidation process and carbon nanotubes process, respectively. The removal efficiency of processes based on physicochemi- cal methods, the highest removal efficiency were magnetic carbon nanotubes, sedimentation, ferrofluid, adsorption and thermal degradation process, artificial foams, afran coagu- lant gas, filtration and centrifugation, Coagulation and flota- tion, thermophotocatalytic process, photocatalytic process, coagulation and flocculation process with sedimentation and filtration, coagulation and sedimentation process, coag- ulation and filtration process, organocells, laser beam and sunlight and nano-ferrofluid, respectively. In the processes based on biological methods, the highest removal efficiency were sequencing batch reactor, activated sludge process, wetland process, oyster, periphytic biofilter and Zalarion- maritimum mushroom, respectively. Also, in the compari- son of the removal efficiencies of the processes based on integrated methods, the highest removal efficiency were the wetland with vertical flow, A2/O, secondary clarifier, denitri- fication, UF, O3, UV, flotation with dissolved air, adsorption and electrocoagulation, activated sludge, extended aera- tion, membrane biological reactor process, oxidation chan- nel system and rapid sand filter, trash removal, granulation 1 3

  8. Journal of Environmental Health Science and Engineering Conclusion study of “Performance of single media rapid sand filter to remove microplastics” that uses rapid sand filter (RSF) with silica sand to remove plastic bags and pieces of rubber, with sizes from 10 to more than 500 micrometer; the removal efficiency in this method for different effective sizes (ES) of filter media varied from 90.6 to 97.7% [15]. Also, in a study conducted by Wang et al. in 2020 on the use of filters containing biochar and sand filters in the filtration of spheri- cal polystyrene microplastics; for all biochars, the filter effi- ciency for removing spherical microplastics was higher than 95% [17]. The study conducted by Shen et al. in 2022 on “Removing microplastics from wastewater by electrocoag- ulation process” showed that the electrocoagulation is used to remove microplastics of polyethylene, polymethyl meth- acrylate, cellulose acetate and poly Propylene with efficien- cies of 82%, 74%, 92% and 90%, respectively, introduced this method as a high efficiency process to remove micro- plastics [31]. The study of Tang et al. in 2021 on the use of magnetic carbon nanotubes (M-CNT) method to remove microplastics from aqueous solutions showed that the effi- ciency of removing microplastics along with increasing the dose of M- CNTs increased and reached nearly 100% within 180 min. The analysis of the mechanism clearly showed that the adsorption of M-CNTs by polyethylene is due to the strong hydrophobicity of microplastics. Therefore, accord- ing to the specified characteristics of M-CNT, it shows that they can be used as an efficient, economical and environ- mentally friendly material to remove microplastics in aque- ous environment recovery and wastewater treatment [50]. In a study conducted by Lee and Kim in 2018 in biologi- cal wastewater treatment facilities to remove microplastics; showed that more than 98% of microplastics were removed in the A2/O, SBR and bioreactor [52]. Among the strengths of this study compared to previous studies, the following can be mentioned: The removal efficiency of the four dominant types of micro- plastics, polyethylene, polystyrene, polypropylene and poly- ethylene tetraphthalate, were compared in selected studies, and the most effective methods used to remove polyethylene microplastics were integrated, physical, physicochemical, chemical and biological methods, respectively. Regard- ing the removal of polystyrene microplastics, the methods of integrated, biological, physical, physicochemical and chemical were highly efficient, respectively. In the removal of polyethylene tetraphthalate microplastic, the methods of physicochemical, integrated, physical, chemical and bio- logical and for the removal of polypropylene microplastic, the methods of physicochemical, integrated, biological and chemical showed high performance, respectively. Examining the average removal efficiency of microplas- tics in each of the physical, chemical, physicochemical, biological and integrated methods for different groups of microplastics, the removal efficiency in the processes based on the integrated method is 88.63%, in the physicochemical method 80.44%, in the biological method 75.23%, in the chemical method 74.38% and in the physical method equal to 73.76%. Also, due to lack of quantitative data informa- tion for some subgroups of removal method categories, it will be difficult to summarize the best removal method in all categories. Therefore, with respect to that point, we have concluded that the “integrated methods” as the best removal method based on the average removal efficiencies in differ- ent types of MPs. Therefore, highest efficiency of removing microplastics was in the processes based on the integrated method (PE, PS, PP using wetland with vertical flow and PET using membrane biological reactor), and the lowest efficiency was in the physical method. Finally, it can be concluded that dif- ferent processes in physical, chemical, physicochemical, biological and integrated methods are able to remove differ- ent microplastics with high efficiency from aqueous envi- ronments and in order to reduce their hazardous effects on health and environment, these processes can be easily used. ● In the present study, all the processes used in the selected articles to remove microplastics in aqueous environ- ments are classified according to the type of process into physical, chemical, physicochemical, biological, and integrated methods, and different methods were com- pared based on the efficiency of microplastic removal; ● In this study, the most appropriate and practical pro- cesses and methods for removing microplastics from aqueous environments until 2022 were investigated, summarized and presented. Limitations and strengths of the study Some of the limitations of the study are given below: ● Publication bias resulting from the exclusion of some types of study designs from the systematic review; ● Lack of access to articles or full version of articles in databases. 1 3

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Biodegradable and re-usable sponge materials made from chitin for efficient Among the strengths of this study compared to previous studies, the following can be mentioned: 4. ● In the present study, all the processes used in the selected articles to remove microplastics in aqueous environ- ments were categorized based on the type of process into physical, chemical, physicochemical, biological and integrated methods, and their removal efficiency was compared ; ● In this study, the best processes and different methods for removing microplastics from aqueous environments were summarized and presented by comparing the effi- ciency of removing processes; ● In this study, the latest technologies used in the removal of microplastics from aqueous environments in the world and Iran were examined in detail; ● Low cost of the study process. 5. 6. 7. 8. 9. Acknowledgements The authors gratefully acknowledge the assis- tant of Department of Environmental Health Engineering, School of Health, Iran University of Medical Sciences (IUMS). Authors’ Contributions A.A. conducted the experiments and wrote the manuscript, M.Gh. supervised and supported and edited the manu- script, Sh.Dj. designed methodology and advised epidemiological and statistical methods, M.F. observed and advised the scientific content of the paper. All authors have read and agreed to the published version of the manuscript. Funding Not applicable. Data Availability All data generated or analyzed during this study are included in this published article. Declarations Ethics approval and consent to participate this study has been ap- proved by the ethical committee of The Iran University of Medical Sciences (IUMS). Consent for publication Not applicable. Conflict of interest The authors declare no conflict of interest. References 1. Esfandiari A, Mowla D. 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