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Onsite wastewater treatment changes the microplastics that escape retention

In Beijing, onsite treatment installations serving two toilets trapped many microplastics, while outgoing particles shrank and acquired less regular shapes. A peer-reviewed field study also found surface oxidation and changes in plastic additives. The work follows physical and chemical transformations alongside particle counts, within the size range that the instruments could measure.

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An open green wastewater-treatment tank with visible water and pipework stands beside a brick public toilet block in a sunlit tree-lined courtyard.

Two onsite systems retain many plastic particles

A field investigation published as a single peer-reviewed study measured microplastic changes during onsite toilet-waste treatment in Beijing, China. The installations served residents and visitors in the Fangshan and Pinggu districts. Researchers sampled water entering and leaving the systems and classified plastic particles using laser infrared imaging. The measured particles were larger than twenty micrometres.[1]

Retention ranged from 53.7 per cent to 77.1 per cent. Material can move into solid compartments, and sludge was periodically taken to another treatment facility. The installations differed: anaerobic and aerobic treatment took place in one stage at the first site and in two stages at the other.[1]

Surviving particles become smaller and more irregular

The outgoing water contained smaller particles with less regular shapes. Their surfaces showed oxidation. Mass-spectrometry screening examined candidate plastic additives, and separate measurements confirmed increases in some phthalates. Statistical analyses linked chemical profiles with particle properties. The work therefore followed the state of the surviving plastic alongside changes in particle abundance.[1]

Treatment conditions differ between the installations

Water remained in the two systems for approximately five days and two and a half days. During the initial operating period, the advanced units for ultraviolet and electrochemical treatment remained inactive. These different configurations and residence times frame the comparison between the facilities. The findings cover two installations and the measured size range; human exposure and health effects were not assessed.[1]

References

  1. News sourceNature CommunicationsOnsite wastewater treatment retains microplastics while changing survivors↩1↩2↩3↩4
Space and explorationEnergy transition and climate

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