Evaluating the effects and removal efficiency of microplastics at Daasport wastewater treatment plant: the case of Gauteng province, South Africa

Abstract

High concentrations of microplastics (MPs) are discharged into the nearby surroundings via the wastewater treatment plant (WWTP), which is the major cause of environmental pollution. Therefore, this study focused on the investigation of the MPs removal efficiency of WWTPs at the Daasport WWTP in the Gauteng province in the Republic of South Africa. The water samples were collected and placed into glass conical flasks, to which 30% hydrogen peroxide and 0.05 M iron sulfate were added to facilitate the breakdown of organic matter. The mixtures were then heated to 75 °C for digestion, and a density separation was carried out using a saturated sodium chloride solution for a duration of 12 to 24 h to isolate the MPs. Under the characterization of MPs using Fourier transform infrared (FTIR) spectroscopy, four polymers were detected: polyamide (PA), polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET). The MPs were mainly found as fibers, fragments, and films, comprising 70%, 23%, and 7% of the total MPs, respectively. The size ranges of the MPs detected in the WWTP varied from 198 to 3400 μm. The findings indicated that the average concentration of MPs entering the WWTP was 69 ± 13 MP/L, whereas the amount of MPs in the discharged effluent was found to be 13 ± 8 MP/L. Predominantly, about 80% MPs removal rate was noted, with the majority being eliminated at various stages of the WWTP. However, some MPs were still found in the effluent and released into the environment. Therefore, these findings provide insight into WWTP management strategies for MPs removal, and post-treatments of the effluent are recommended before being released into the environment.