Average daily flow of microplastics through a tertiary wastewater treatment plant over a ten-month period

Abstract

Microplastics (MPs, <5 mm in size) are classified as emerging contaminants but treatment processes are not designed to remove these small particles. Wastewater treatment systems have been proposed as pathways for MPs pollution to receiving waters but quantitative and qualitative data on MP occurrence and transport remains limited, hindering risk assessment and regulation. Here, for the first time, the stepwise abundance and loading of MPs (60-2800 µm) in a tertiary wastewater treatment plant in the UK was assessed by sampling from May 2017 to February 2018. Microplastics were found in all sampling campaigns, with an average inflow of 8.1 x 10 8 (95% CI, 3.8 x 10 8 to 1.2 x 10 9 ) items day -1 . Their prevalence decreased from influent to final effluent. Overall abundances decreased on average by 6%, 68%, 92%, and 96% after the pre-treatment, primary, secondary, and tertiary treatment stages respectively, although considerable variability occurred throughout the year. Sufficient particles remained in the treated effluent to generate an average discharge of 2.2 x 10 7 (95% CI, 1.2 x 10 7 to 3.2 x 10 7 ]) particles day -1 to the recipient river. Secondary MPs were predominant, while primary MP abundances were minimal. Fibres comprised 67% of all items, followed by films (18%) and fragments (15%). Chemical characterisation confirmed the presence of different types of polymers, with polypropylene fibres and fragments most abundant (23%). This research informs understanding of how wastewater effluent may channel MPs to the natural environment and their composition, and helps understand control points for optimising advanced treatment processes.

Presence and fate of microplastics in the water sources: focus on the role of wastewater and drinking water treatment plants

“…Conclusively, influent load of MPs to WWTPs and their characteristics seem to be possibly influenced by various factors: source of MPs (industrial, domestic…), population served, sewage collecting system, [87].…”

The Effect of Wastewater Treatment Plants on Retainment of Plastic Microparticles to Enhance Water Quality—A Review

“…, isolation and quantification difficult[117]. There are but few studies that address the MP flux through a WWTP over a long period of time[91] [111]. Additionally, most studies have solely looked at MP concentrations in the WWTP influent and final effluent, but only few studies have investigated the MP concentrations at the different treatment stages[90] [117].…”

Optimising sample preparation for FTIR-based microplastic analysis in wastewater and sludge samples: multiple digestions

“…In comparison, the body of knowledge in terrestrial and freshwater ecosystems is limited, although several studies addressed this issue in recent years [6,[14][15][16][17]. Among several other land-based sources of MP pollution, wastewater treatment plants (WWTPs) have received attention as they have been identified as terrestrial pathways of MP emissions into aquatic ecosystems [4,5,[18][19][20][21][22][23][24][25][26][27]. Therefore, assessment of the presence and quantification of MPs in effluent discharges and sewage sludge applied to land is a high priority, to enable the risks to be assessed.…”