Microlitter in sewage treatment systems

A Nordic perspective on waste water treatment plants as pathways for microscopic anthropogenic particles to marine systems

image of Microlitter in sewage treatment systems

The report presents results from a study on the role municipal sewage treatment plants (STPs) have as entrance routes for microplastics and other microlitter particles to the marine environment. Microlitter concentrations were analysed in waste water before and after treatment in the STPs, and in the recipient waters where the treated waste water is discharged.

Municipal waste water was found to contain a substantial amount of microlitter, but in STPs equipped with chemical and biological treatment most of the litter particles were retained in the sewage sludge. This reduces the impact on the recipient water, but if the sludge is used as fertilizer on farm land the microlitter will still reach the environment. Efforts to reduce the microlitter concentrations should therefore preferably be done in households and other locations where the waste water is originally being formed.




The purpose of the present study was to investigate the importance of STPs as gateways for microlitter particles to the environment. The work was divided into two parts carried out in separate years, 2014 and 2015. The first year concentrations and composition of microlitter in waste water at six STPs in Sweden, Finland and Iceland was investigated. The second year studies were done on microlitter in the recipient water for one of the STPs from each country. The investigated particles included microplastics the litter group that generally is considered to be the most problematic, but also non-synthetic anthropogenic fibres e.g. cotton, viscose, wool, were analysed since these are commonly found in field samples.


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