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Fate, characteristics, and potential threat of microplastics in sludge under various dewatering treatments
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Researchers compared four different sludge dewatering treatments used at wastewater plants and examined how each process affected the microplastics trapped in the sludge. They found that advanced oxidation treatments altered the surface properties of the microplastics and increased their ability to absorb heavy metals. The findings raise concerns that certain sludge treatment methods could make microplastics more environmentally hazardous when the treated sludge is disposed of or reused.
Microplastics (MPs), an emerging environmental pollutant, have been found in wastewater sludge with increasing frequency. Their occurrence, surface properties, and adsorption characteristics may be altered during various sludge dewatering processes. This study explored and compared the performance of four types of sludge dewatering processes (FeCl + CaO, Fe + HO + CaO, Fe + peroxymonosulfate (PMS) + CaO, and Fe + CaO + CaO) in improving sludge dewaterability, the fate and characteristics of MPs during treatments, and their effect on the adsorption of heavy metals by aged MPs. Results showed that iron-based advanced oxidation processes (Fe-AOPs) indicated superior performance in improving sludge dewaterability compared to conventional FeCl + CaO treatment, as evidenced by the water content of sludge cakes being reduced to below 54.0 % (w/t) in Fe-AOPs. Fe + PMS + CaO and FeCl + CaO effectively reduced MPs concentrations in both dewatered sludge and filtrate, thereby mitigating potential environmental risks. The potential risk associated with heavy metal adsorption onto treated MPs was greater for Fe + PMS + CaO than for FeCl + CaO. In summary, Fe + PMS + CaO offered a feasible method for sludge dewatering and MPs removal, particularly suited to sludge with low heavy metal concentrations. FeCl + CaO treatment effectively mitigated co-toxicity between heavy metals and MPs, proving more suitable for sludge with high heavy metal content. This study offers new insights into the selection of appropriate sludge treatments regarding MPs.
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Researchers studied how mechanical dewatering of sewage sludge affects the microplastics embedded within it, including their physical changes and leaching behavior. They found that the dewatering process roughened microplastic surfaces, reduced particle sizes, and altered their chemical properties due to dewatering agents and mechanical forces. The study also showed that leachates from these processed microplastics could negatively affect activated sludge performance in treatment systems.
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Researchers evaluated how sludge drying and dewatering processes affect microplastic abundance and characteristics at two wastewater treatment plants in Morocco, collecting samples across multiple treatment stages. The study identified specific sludge processing steps that concentrate or transform microplastics, with implications for managing microplastic emissions when treated sludge is land-applied.
The Effects of Microplastics on Floc Formation, Nutrient Removal and Settleability in Wastewater Treatment
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Researchers examined the interactions of microplastics with activated sludge in wastewater treatment plants, investigating effects on floc formation, nutrient removal efficiency, and settleability to understand how microplastic contamination may compromise treatment performance.
Transfer of microplastics in sludge upon Fe(II)-persulfate conditioning and mechanical dewatering
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Researchers investigated how Fe(II)-persulfate conditioning and mechanical dewatering of sewage sludge affect microplastic fate, finding that these processes can fragment larger plastic particles, increasing the number of smaller microplastics that may subsequently be released during sludge land application.
Transport and accumulation of microplastics through wastewater treatment sludge processes
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Researchers tracked microplastic concentrations through each stage of wastewater treatment sludge processing — including thickening, anaerobic digestion, and dewatering — finding that each step altered MP abundance and size distribution, with digestion fragmenting some particles into smaller pieces rather than eliminating them.
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