The course of microplastics before and after UK WWTPs and their release into the environment.

Plastic has become an invasive material in modern human lifestyle and is heavily relied upon as an essential resource. It is identified as one of the chief environmental problems. Although identified primarily into marine environments, the main source of the plastics is from land and is discharged into our shores via rivers. To be able to lessen their impacts into the ocean, it is important to understand how to reduce their production upstream. This research is focussing on the fate of the secondary microplastics (MP) from when they leave the household with the greywaters to when they are released via the WWTP (wastewater treatment plant) discharges into our urban rivers.

The household laundry of synthetic textiles has been recognised as one of the largest sources of MP production. This counts for most of the MPs leaving our home via greywaters to reach urban WWTPs. Consequently, the study has focussed on MPs released from 24 washing machine loads, consisting of well-catalogued and weighed various combinations of synthetic garments, under “normal wash conditions”. It was determined that an average load can produce up to 93,000 MP fibres per kg, but it was found that heavier loads released fewer MP fibres. Using a full washing load can reduce the number of fibres produced by up to 70%.

To estimate the release of MPs into freshwater rivers from WWTPs, six discharges from urban plants from middle size towns around Greater London have been sampled and analysed. It was found that although MP quantities are very high the numbers vary greatly due to the age and the size of those sites, but also the technique that is used. It results in a range between 0.5 and 18 million MP per hour being released. This highlights that WWTPs are not advanced enough to remove MP pollution, making these discharges the main source into the freshwater environment.

Furthermore, the MP release from plant discharges into rivers is not the main secondary source as up to 98% of the MPs passing through WWTPs might end up as sludge that can later be applied to improve agricultural land for higher crop yields. This creates a major source of MP fibres into our rural rivers upstream of the urban hubs. Not only does this introduce microplastics to terrestrial habitats but it also creates a direct secondary pathway for microplastics to enter surface waters. This study highlights the urgency to update wastewater treatment and disposal practices to tackle the various issues of fibres getting into surface and groundwaters.