Guidance on concrete ways to reduce microplastics in stormwater and sewage

In this report, we have provided an overview of (1) current stormwater management systems and techniques in the Baltic Sea Region, based on mostly Swedish experience, (2) concrete ways to reduce microplastics from stormwater and waste water and (3) simple methodology to monitor riverine inputs of microplastics.

Main findings:
- Constructed free water surface wetlands of varying shapes, age, flow rates and sizes can be very efficient in reducing microplastics from effluents of WWTPs to the water bodies. These new results adds to their already known benefits, such as e.g. pharmaceutical removal, nutrient removal and protection for unwanted releases of untreated water.
- The high MP concentrations found in urban stormwater call for concerns due to the often large and untreated stormwater volumes released to recipient waters.
- Stormwater ponds used as end of pipe solutions show good removal efficiency for microplastics.
- There are relatively simple and verified methods for sampling and analyzing microplastic contents in water.
- If microplastics are to be analyzed for stormwater or sewage it’s very important to include particle sizes smaller than 300 μm, due to their abundance.
CCB proposals:
- wetlands should be considered as an end of pipe solution to reduce microplastic entering the streams, rivers and sea
- monitoring of outgoing water from urban areas stormwater must be developed and implemented
- all WWTP should establish testing of plastic particle content of outflowing water