The wastewater with high microplastics concentrations: characteristics of microplastics and removal methods

ABSTRACT

(i) Four main wastewater sources of high microplastics concentration, including laundry wastewater, wastewater from plastic recycling processes, leachate from landfills and sludge from wastewater treatment plants. (ii) Four main microplastics types, including polyethylene, polypropylene, polystyrene, and polyester. (iii) Four main shapes, including fibers, fragments, films, and pellets. (iv) Six main physicochemical processes, including membrane, filtration, flotation, flocculation-coagulation, adsorption and advanced oxidation-photodegradation. (v) Three main biological processes, including microalgae, bacteria, and marine organisms.

Microplastics (MPs) pollution from wastewater presents a global challenge, causing detrimental impacts on human health and ecosystems. This review initially focuses on the occurrence and distribution of MPs, their potential negative impacts, and characteristics of four main wastewater sources (namely wastewaters from laundry, plastic recycling processing, landfill leachate, and wastewater treatment plant sludge). This review then critically analyzes existing technologies for MPs removal, their efficiency, feasibility, and limitations. For MPs sources, sewage sludge is identified as the largest source of MPs waste entering the environment. Recent studies show that MPs could be removed effectively by physicochemical methods (coagulation, adsorption, filtration, flotation, advanced oxidation, and membrane filtration) under suitable environmental conditions. However, MPs are not removed effectively by the conventional biological method in wastewater treatment facilities. Membranes can achieve very high removal efficiency for all MP sizes, especially when combined with other treatment methods. The performance of flotation and sand filtration, conversely, is highly dependent on MP sizes. The main challenges of flotation and flocculation/adsorption are the operation's complexity and residual management, respectively. This review proposes recommendations to enhance the effectiveness of MPs removal methods and emphasizes the need for standardized MPs sampling and analysis protocols.