Abundance of Microplastics in Wastewater Treatment Sludge

Wastewater treatment plants (WWTPs) have been regarded as feasible interceptors of microplastics, which have now contaminated all spheres of the environment. The microplastics removed from WWTPs are frequently trapped in the sludge produced. This article aims to examine the abundance of microplastics in the sludge of WWTPs in different regions by reviewing the relevant scholarly papers published between 2016 to 2022. The papers were retrieved from three databases, namely Web of Science, Scopus, and ScienceDirect. WWTPs receive influents containing microplastics whose abundance differs significantly in relation to the population density, urbanization level, and land use of the areas served. Depending on the water treatment strategies and the efficiencies of the WWTPs, a large proportion of the microplastics in the influents is trapped in the sludge, giving a common sludge-to-influent abundance ratio of 0.02 to 0.77, though a ratio of 3.4 has been reported for recycled activated sludge. Sludge treatment affects the final abundance of microplastics therein. However, a relationship between the abundance of microplastics in influents and that in sludge cannot be established. The reutilization of sludge as fertilizer introduces microplastics back into the environment and significantly compromises the potential of WWTPs as interceptors and sinks of microplastics. This review calls for strategies and technologies to reduce, if not remove microplastics in the sludge of WWTPs. It suggests that future research could take this path to optimize the role of WWTPs as sinks of microplastics. Doi: 10.28991/HEF-2022-03-01-010 Full Text: PDF