Microplastic pollution in wastewater treatment plants in the city of Cádiz: Abundance, removal efficiency and presence in receiving water body

Abstract

Wastewater treatment plants (WWTPs) have been appointed as one of the main sources of microplastics (MP) into marine ecosystems. The aim of this research work has been to study the influent and effluent of two WWTPs, both located in Cádiz, with different wastewater source (industrial and urban), as well as the receiving water bodies where the facilities discharge their sewage. MP were collected, extracted from wastewater matrixes and analysed according to the abundance, shape, size, and type of polymer, along with the removal rates of MPs in the plants. Subsequently, the data obtained on both WWTPs were compared, the main difference among the WWTPs was the amount of microplastics found in the wastewater, as well as the presence of polymers with resins from industrial activities. The results from this study established that the most representative form was fibers; about the size, 100–355 μm fraction was the most abundant, followed by 355–1000 μm and finally the size among 1000–5000 μm. Regarding to the type of polymers, 17 were identified using attenuated total refraction Fourier-transformed infrared spectroscopy (ATR-FTIR). Further, PVC, PE, EAA and HDPE were the largest found polymers. The presence of MPs in the influent varied from 645.03 ± 182.24 MPs/L to 1567.49 ± 413.18 MPs/L in the urban and industrial WWTP respectively; in the effluent, it varied from 16.40 ± 7.85 MPs/L to 131.35 ± 95.36 MPs/L. The removal rate overcome the 90% in all the samples. Receiving water bodies presented heterogeneous abundance of microplastics 6.64 ± 2.71 MPs/L and 0.83 ± 0.26 MPs/L in the zones close to IWWTP and UWWTP discharge point. The results obtained shows that despite the elimination efficiency in the WWTPs studied, these facilities act as a significant source of MPs into aquatic ecosystem due to large flow of water discharged.