Distribution characteristics of microplastics in storm-drain inlet sediments affected by the types of urban functional areas, economic and demographic conditions in southern Beijing.

A storm-drain inlet is an important link in the transport of microplastic pollutants in urban rainwater runoff. In three functional districts (agricultural, commercial, and residential) from Beijing South 2nd Ring Road to South 6th Ring Road, microplastics in storm-drain inlet sediments were analyzed for abundance and characteristics. The abundance of microplastics in the collected samples ranged from 1121 ± 247 items kg-1 to 7393 ± 491 items kg-1. Among the sample areas, the commercial area had the greatest abundance (11094 items kg-1), while the agricultural area had the lowest (833 items kg-1). The microplastics in the samples were mainly fragments, accounting for 50.4%. Microplastics of less than 1 mm accounted for 74.8%. The color of microplastics was diverse, with colored MPs accounting for 26% and transparent ones for 47.8%. Most of the polymers detected were PET, PS, and PP, which are the most commonly used polymers. Overall, the results provide baseline data on microplastic pollution and its associated risks, in addition to guidelines for controlling runoff pollution.

Improving sludge dewaterability via Fe2+ chelated citrate activated peroxydisulfate oxidation.

Citrate (Ct) was chosen as a typical chelator used in the Fe2+-peroxydisulfate (PDS) process to improve sludge dewaterability. The PDS-Fe2+-Ct process exhibited better performance in sludge dewatering than PDS-Fe2+. Specifically, with a PDS dosage of 1.2 mmol/g VS, the molar ratio of PDS/Fe2+ and Ct/Fe2+ were 4:5 and 1:4, respectively, the capillary suction time decreased from 155.8 to 24.8sec, and the sludge cake water content decreased from 82.62% to 64.11% (-0.06MPa). The oxidation led to a reduced negative charge and a decrease in particle size. The enhanced sludge dewaterability and changes of sludge properties were attributed to the decomposition of extracellular polymeric substances, and it was explored by protein, polysaccharide, 3D-EEMs, and FT-IR. Additionally, the quenching experiments of radical species demonstrated that SO4-• played a more important role than •OH, and its productivity was improved with the addition of Ct. Moreover, the reasons for the improved productivity of radicals with the addition of Ct were discussed. The results of this study could serve as a basis for improving sludge dewatering using the PDS-Fe2+-Ct process and suggest that the addition of Ct may improve the productivity of SO4-• in the activation of PDS via Fe2+.