Characterization and removal efficiency of microplastics in sewage at a conventional facultative pond

Abstract Research on microplastics in wastewater has largely focused on conventional and advanced wastewater treatment plants, with little emphasis on oxidation ponds. This study examines the fate and characteristics of microplastics in a wastewater oxidation pond in Penang, Malaysia. Microplastics were monitored at all treatment stages by collecting 40 litres (L), 60 L, and 165 L of raw influent, preliminary effluent, and final treated effluent, respectively, using a stainless-steel bucket as an improvised volume-reduction sampling equipment. The microplastics concentration in the raw influent was 1.78 MPs/L, which was reduced to 0.67 MPs/L in the final treated effluent, resulting in a removal rate of 62.36%. The microplastic shapes detected in the pond were fibres, films, foams, and fragments, with fibres being the dominant type (42.25%) in the raw influent. Similarly, fibres and films had an equal distribution in the preliminary effluent, while fibres remained the dominant shape in the final treated effluent. The polymer composition of the detected microplastics consisted of polypropylene (PP) and Acrylonitrile Butadiene Styrene (ABS), with PP being the dominant polymer at all treatment stages in the pond. Among the seven identified microplastic colours, black had the highest proportion (28.17%) in the raw influent, transparent microplastics were dominant (28.12%) in the preliminary effluent, and red accounted for 45.45% of microplastics in the final treated effluent.