Microplastic abundance and removal via an ultrafiltration system coupled to a conventional municipal wastewater treatment plant in Thailand

A wastewater treatment plant is one of the land-based sources of microplastics in freshwater environments. A conventional wastewater treatment plant alone is not designed for microplastic removal. This study evaluates the abundance and microplastic removal efficiency of a conventional wastewater treatment plant and the load daily released to water environment. It also investigates the effect of coupling a pilot-scale ultrafiltration system. Samples were collected at each unit operation by grab sampling. Sludge samples were collected from return activated sludge after the final clarifier to find microplastic pollution levels that might contaminate agricultural soil. The results showed that on average, 77 +/- 7.21 particles/L were found in the influent, and 10.67 +/- 3.51 particles/L were discharged with the final effluent, resulting in 86.14% overall removal efficiency in a traditional treatment system. When an ultrafiltration unit was taken into consideration, the number of microplastics in the effluent reduced to 2.33 +/- 1.53 particles/L, which increased the removal efficiency up to 96.97%. The abundance of microplastic particles in sludge samples generated from the final clarifier was 2.63 +/- 1.26 x 10(4) particles/kg (dry weight). The most dominant group was 0.05-0.5 mm, and fibers accounted for more than 60% of total microplastics at every sampling point. The results from spectroscopic analysis showed that polyethylene terephthalate (PET) was the major type of microplastics, followed by polyethylene (PE) and polypropylene (PP). This study shows that advanced technology in tertiary treatment plants could substantially remove microplastic pollution in wastewater. Moreover, the absence of primary sedimentation tank can also influence removal of microplastics.

Automated summary

This study evaluates the abundance and removal efficiency of microplastics in a conventional wastewater treatment plant, finding an overall removal efficiency of 86.14%. Additionally, the use of a pilot-scale ultrafiltration system increases the removal efficiency to 96.97%.