Wastewater treatment plants (WWTPs) are generally considered to be an important source of microplastics (MPs) release into the aquatic environment. When MPs are combined with other pollutants in water, they may cause great harm. However, MPs are not ideal for removal in WWTPs, where they escape and eventually accumulate in the environment. As for the transport and fate of MPs in different treatment stages of WWTPs, there are some differences in existing studies. Meanwhile, there is still a lack of comparative study on the removal effect of MPs in WWTPs, and there is no clear definition on the source of MPs in WWTPs and the proportion of each source. 

Researchers from Wuhan Botanical Garden conducted a detailed investigation of the MPs in and out of water and sludge from two WWTPs in the urban and suburban areas of Wuhan. By comparing the occurrence and removal of MPs in two WWTPs in Wuhan city, the characteristics of MPs in toothpaste, facial cleanser and laundry wastewater were clarified in order to evaluate the potential sources of MPs in urban wastewater.  

The abundance of MPs in the wastewater of two WWTPs dropped sharply, which can be attributed to the wastewater sources and treatment technologies used in WWTP. The fiber, fragment, and microbead presented in the three sources of household wastewater (toothpaste, facial cleanser and laundry wastewater) and WWTPs had similarity in shape, and further the main component of MPs in household wastewater and WWTPs was polyvinyl chloride through Raman spectrum analysis. 

Interestingly, large amounts of microbeads were only found in frosted cleansers, but no microbeads in toothpaste. Fibers in laundry waste mostly made up the bulk of MPs in household wastewater. It has further been estimated that the daily discharge of MPs from household wastewater to WWTPs in China is 9.1×10¹⁰.  

Results indicate that the MPs in household wastewater mainly contribute to the MPs in wastewater of WWTP, therefore, the use of MPs in the personal care products should be banned or alternatives of primary MPs use in these products must be developed. 

This work was supported by the National Natural Science Foundation of China. Relevant research results have been published in Science of the Total Environment entitled "Microplastics in wastewater treatment plants of Wuhan, Central China: abundance, removal, and potential source in household wastewater". 

Photographs of MPs particles in WWTPs laundry wastewater and household wastewater (a, b, c, d: MPs from WWTPs; e, f, g, h: MPs from household wastewater) (Image by TANG Na)