Microplastics are generated from plastic waste in landfills due to physical, chemical, and biological effects, and eventually enter into the leachate. Leachate is a potential source of environmental microplastics which has not been emphasized. Here, we summarized the investigation of microplastics in leachate in 9 countries from 28 papers, provided a comprehensive review of the sampling, detection, and separation of microplastics in leachate, and elaborated on the quality control in each process. There are more than forty types of microplastics in leachate, with diverse shapes, wide size distribution, and concentrations of 0–25 items/L. Commonly used techniques are FTIR, Raman, SEM, and py-GC–MS for characterizing microplastics, while standardization of micro- or nanoplastics for leachate with a complex composition should be further studied. We also discussed in depth the degradation mechanism of microplastics in advanced oxidation processes (AOPs). Microplastics can be decomposed into small molecules such as aldehydes and ketones, and some can even eventually be degraded into CO₂ and H₂O in AOPs, which may be further implemented in leachate treatment plants. This review provides the scientific fundamentals for understanding the microplastics in landfill leachate and proposes removal strategies for future research.

Chemical precipitation using magnesium salt is an effective technology for recovering phosphorus and ammonium nitrogen from wastewater. Effects of pH, Mg/P ratio, stirring rate, and seed crystal (SC) dosage on phosphate removal efficiency (PRE) and average particle diameter (APD) of precipitates were investigated for reject water from sludge thickening and dewatering process in municipal wastewater treatment. Response surface methodology was applied to understand the significance and the interactive effects of reaction factors. The increases in Mg/P ratio, stirring rate, and SC dosage were in favor of phosphate removal from reject water. pH is the dominant factor for phosphate removal by magnesium, followed by Mg/P and stirring rate, while SC dosage has the least effect on PRE and APD. Kinetic analysis showed that both pH regulation and SC addition could accelerate the reaction rate. The optimum conditions were obtained at pH 10.4, Mg/P of 2.0, stirring rate of 150 rpm, and SC dosage of 26.7 mg/L, with PRE of 95.9%, APD of 104 μm, and final mass of precipitate of 936.3 mg/L. X-ray diffractometer analysis revealed that the increase in pH resulted in the increase in crystallinity and the conversion of struvite to calcium pyrophosphate, and the precipitates of reject water were struvite at pH < 10.5.