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A Comprehensive Modeling of Microplastic Emission from Wastewater Treatment Plants to the Sea via Rivers in China
Summary
Researchers built a comprehensive model of microplastic emissions from over 10,000 wastewater treatment plants across China, estimating that treated wastewater releases roughly 45 million kilograms of microplastics annually. Remarkably, untreated sewage contributes a comparable amount, indicating that expanding treatment capacity is critical. After accounting for river retention, an estimated 41 to 82 million kilograms of microplastics still reach the sea each year.
Wastewater treatment plants (WWTPs) are significant sources of microplastic (MP) emissions. In order to quantify the potential MP emission from WWTPs, a database of more than 10,000 WWTPs in China with an estimated MP emission rate was built. The MP riverine retention after emission was also estimated based on Stokes' law for both fragments and fibers. The results show that the mass of MPs discharged from WWTPs is (4.48 ± 7.48) × 107 kg, yet the amount of MPs released from untreated sewage is (4.55 ± 3.00) × 107 kg, which is comparable to that of treated wastewater, indicating the capacity of wastewater treatment should be further strengthened. The flux of MPs into the sea after river interception is between 4.08 × 107 kg and 8.20 × 107 kg with 14-27% being directly discharged to the sea within 20 km from the shore.