Surfactant-assisted air flotation: A novel approach for the removal of microplastics from municipal solid waste incineration bottom ash.

The potential for the presence of microplastics (MPs) in municipal solid waste incineration bottom ash (MSWI-BA) has not been fully explored. In this study, surfactant-assisted air flotation separation in aqueous media was used to examine the removal of MPs and other pollutants from different particle size fractions of MSWI-BA. The use of 1 mmol L-1 sodium dodecylbenzene sulfonate (SDBS), at a liquid-solid ratio of 60:1, increased by 66 % the quantity of MPs floated from the MSWI-BA 0-0.3 mm fraction, as compared to pure water. The four most common shapes of the floated MPs were pellets, fragments, films and fibers, and the major polymers were polypropylene, polyethylene, polymethyl methacrylate, and polystyrene (approximately 450 µg g-1 BA). The flotation of <10 µm MPs increased by up to 7 % using this method compared to flotation in saturated NaCl solution. Reuse of the flotation solution with the SDBS concentration maintained resulted in reduced MPs removal abundance by 22 % in the fourth use as compared to the first use. MPs removal correlated positively to SDBS concentration and negatively to turbidity. Precipitation from the fourth flotation solution was evaluated using polyacrylamide (PAM) and polyaluminium chloride (PAC) for the purpose of promoting the regeneration and recycling of the flotation solution. This treatment reduced MPs abundance, turbidity, and potential heavy metals in the recycled flotation solution. It is estimated that 3.4 kg of MPs could be removed from each ton of MSWI-BA. The findings of this study contribute to a better understanding of the redistribution of MPs during MSWI-BA pre-use treatment and provides a reference for the practical application of surfactant-assisted air flotation separation.

Microplastics contamination associated with low-value domestic source organic solid waste: A review.

Waste activated sludge and food waste are two typical important domestic low-value organic solid wastes (LOSW). LOSW contains significant organic matter and water content resulting in the transboundary transfer of liquid-solid-gas and other multi-mediums, such that the complexity of microplastics (MPs) migration should be of greater concern. This article provides a review of the literature focusing on the separation and extraction methods of MPs from LOSW. The occurrence and source of MPs are discussed, and the output and impact of MPs on LOSW heat and biological treatments are summarized. The fate and co-effects of MPs and other pollutants in landfills and soils are reviewed. This review highlights the migration and transformation of MPs in domestic source LOSW, and future perspectives focused on the development of a unified extraction and analysis protocol. The objective of this review is to promote the technological development of decontamination of MPs in LOSW by sufficient understanding of the fate of MPs, their interaction with coexisting pollutants and the development of targeted preventive research strategies.

Transfer of microplastics in sludge upon Fe(II)-persulfate conditioning and mechanical dewatering.

Sewage treatment plants act as both sinks and sources of microplastics with elevated concentrations of microplastics accumulating in the sludge. Consequently, the effects of sludge conditioning and dewatering processes on the fate of microplastics need to be clarified. Microplastic characteristics in sludge, before and after advanced oxidation Fe(II)-activated persulfate conditioning were studied using a microplastics dynamic flotation separator (MDFS). In the unconditioned sludge (no dewatering), white and transparent microplastics dominated and seven types of plastic polymer were detected with polyethylene (30.3%) and polypropylene (23.9%) being the main ones. Pellet microplastics were found to be the dominant morphology, accounting for 67.0% of the total number of microplastics. The abundance of microplastics extracted using the MDFS device from the unconditioned (no dewatering) sludge was 320 ± 3 particles g-1 dried sludge, which was greater by 37% than extracted using microplastics static flotation separation. Due to the release of the adsorbed microplastics from the destroyed sludge flocs after conditioning, the abundance of extractable microplastics increased by 19 ± 2% as compared to the unconditioned sludge (both with no dewatering). After filter presses (plate-frame filter, vacuum filter) and centrifuge dewatering, 81-90% of the microplastics were present in the filter cake, of which microplastics <500 µm accounted for more than 80% of the total number. The abundance of microplastics per unit volume of filtrate after filter press dewatering was significantly smaller than after centrifuge dewatering (3.2-4.4 × 103 cf 13.0 × 103 particles L-1, respectively). The difference increments in relative abundance of <10 µm microplastics in the centrifuge filtrate was about twice that of the filter presses. The surface morphology of the microplastics did not change in the conditioning process. This study highlights the need to assess the application of advanced oxidation conditioning which has significant influence on the microplastics distribution via the subsequent sludge dewatering.