Involved Member: Prof. Paul Kwan Sing LAM
In recent decades, marine microplastic pollution has attracted extensive attention from scientific community and the public. Wastewater treatment plants (WWTPs) that are designed to treat industrial and municipal sewage via physical, chemical, and biological processes have been identified as one of the major pathways that transfers microplastics to the aquatic environment. At present, the majority of available studies of WWTPs have focused on analyzing the fates and removal efficiencies of microplastics as a whole, or by each individual treatment process, by measuring their contents in the WWTP influent, effluent, and sludge. It is plausible that the presence of anthropogenic microplastics in sewage may also be prone to change over time. Nevertheless, intra-day variations of microplastic in WWTPs have not drawn much attention. Many researchers have investigated microplastics in WWTP influent by sampling wastewater during a specific time period or by using average data for a few days of sampling, which may lead to estimation errors in actual microplastic abundances, as well as in daily microplastic loads in WWTPs. Hence, a representative secondary WWTP in Hong Kong was selected to investigate the characteristics and intra-day variations in the WWTP influent and to evaluate the daily microplastic loads. Results show that the average microplastic abundances increased from 7.1 ± 6.0 to 12.8 ± 5.8 particles/L and then dropped to 11.6±2.9 particles/L over time. Approximately 80% of the microplastics in samples collected from 9:30–15:00 were polyethylene and polyester, while most samples collected at 17:00 were polypropylene and polyurethane. Microplastic loads exhibited large intra-day variations ranging 6.60 × 108–1.16 × 109 particles/day, indicating that calculated daily microplastic loads based on a specific sampling period may inaccurately estimate the actual daily load.
Reference:
Cao, Y., Wang, Q., Ruan, Y., Wu, R., Chen, L., Zhang, K., & Lam, P. K. (2020). Intra-day microplastic variations in wastewater: A case study of a sewage treatment plant in Hong Kong. Marine Pollution Bulletin, 160, 111535.
