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.




Litter is not only all those visible objects that are found most everywhere in both urban and rural areas, but it also includes the minute non-visible, microlitter. Microlitter particles may be composed of fragments of larger litter objects or they may be particles that were intentionally produced in a microscopic size. What materials are included in the term litter may be debated, but the litter in the marine environment has been defined by the group of experts that work on litter in relation to the Marine Strategy Framework Directive (2008/56/EC): “Marine litter is any persistent, manufactured or processed solid material discarded, disposed of or abandoned in the marine and coastal environment. Marine litter consists of items that have been made or used by people and deliberately discarded or unintentionally lost into the sea and on beaches including such materials transported into the marine environment from land by rivers, draining or sewage systems or winds. For example, marine litter consists of plastics, wood, metals, glass, rubber, clothing, paper etc. This definition does not include semi-solid remains of for example mineral and vegetable oils, paraffin and chemicals that sometime litter sea and shores” (Galgani et al., 2010). Many plastic polymers are extremely resistant to degradation, and once released into the environment they might remain for decades or even centuries.


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