Phytoremediation of Microplastics from Industrial Wastewater

Microplastics (MPs) have truly penetrated every ecological niche and have become near ubiquitous in the environment. This has been possible because of their small size, low density, and a large surface area compared to volume. One of the major contributors to microplastic pollution (MPPs) in the environment has been the humongous quantity of wastewater generated from industries such as textile, chemical, food, leather, dairy, automobile, electronic, construction, etc., daily. Out of this, only a fraction of wastewater is treated by wastewater treatment plants (WWTPs). Even after efficient wastewater treatment, a small number of MPs are released into the environment which significantly contributes to MPPs. These MPs can easily be colonized by pathogenic microbes, forming biofilms and serving as vectors of pollutants in the aquatic environment. This has necessitated the removal of MPs with an efficient yet cost-effective remediation strategy. Many strategies such as the physical segregation of plastic items at the primary stage, valorization of plastic waste, and bioremediation using microbial enzymes have been proposed and studied. Among them, aquatic phytoremediation of wastewater using macrophytes is one such strategy that has been gaining interest in recent years. Simply put, in phytoremediation macrophytes absorb MPs out of contaminated water or soil by trapping and depositing them around the root zone and allowing them to form clusters on root tips. These MPs are then taken up and translocated throughout the plant body, accumulating them in various parts. However, the fate of the MPs is uncertain as there is very little evidence suggesting the degradation of MPs after getting absorbed. Moreover, weak adhesion, desorption, or runoffs due to various environmental factors often make plants the source of MPs. An extensive literature review suggests that some species of aquatic macrophytes have been used for phytoremediation of wastewater out of which few studies have solely focused on MPs removal in a controlled environment. Some studies have also focused on the potential of mixed plant assembly to effectively sequester MPs with careful consideration for the type of macrophyte used, and a few studies investigated the toxic effects of MPs on the macrophytes. This chapter focuses on the aquatic macrophytes and microalgae which have been studied for the removal of MPs from treated wastewater, the mechanisms employed by those species to sequester MPs, various parameters contributing to the adhesion of MPs to the macrophyte, effect of macrophyte planting systems, and the role of microbial biofilm formation in phytoremediation.