Identification and quantification of microplastics in wastewater treatment plants by spectroscopic and microscopic techniques in Johannesburg East, South Africa

Abstract

The occurrence of microplastics in water, their chemistry, physical characteristics, and the efficiency of public wastewater treatment work (WWTW) processes in the removal of microplastics are investigated. Samples were collected from the period 2021 December to 2022 September from two WWTWs in Johannesburg East using 24-h autosamplers. The microplastics were imaged using polarised optical microscopy (POM) and the images were processed using image J 1.53 K to determine the particle counts. The total concentration of microplastics at WWTW A was 3,098 MP/L while WWTW B had 3,561 MP/L. The microplastics identified across the seasons were dominated by angular, fibres, fragments, and films. Fourier transforms infrared (FTIR) spectroscopy identified the polymers such as polyethylene, acrylic, polyethylene terephthalate, and polystyrene in WWTW A and B influent while identifying the polymers such as polystyrene, polyacrylamide, polypropylene, polycarbonate, acrylonitrile butadiene styrene, poly(ethyl cyanoacrylate), carboxyl, poly(ethylene terephthalate), polyethylene, poly(methyl methacrylate), and cellulose in the final effluent. Scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDX) identified Cr, Ca, Fe, Al, Na, Mg, Zn, Cl, P, S, and silicon as additives to microplastics with high-intensity peaks of oxygen and carbon. It is recommended to monitor and regulate microplastics in discharged effluents from WWTWs to minimise environmental pollution.