This study on the removal of microplastics during different wastewater treatment unit processes was carried out at Viikinmäki wastewater treatment plant (WWTP). The amount of microplastics in the influent was high, but it decreased significantly during the treatment process. The major part of the fibres were removed already in primary sedimentation whereas synthetic particles settled mostly in secondary sedimentation. Biological filtration further improved the removal. A proportion of the microplastic load also passed the treatment and was found in the effluent, entering the receiving water body. After the treatment process, an average of 4.9 (±1.4) fibres and 8.6 (±2.5) particles were found per litre of wastewater. The total textile fibre concentration in the samples collected from the surface waters in the Helsinki archipelago varied between 0.01 and 0.65 fibres per litre, while the synthetic particle concentration varied between 0.5 and 9.4 particles per litre. The average fibre concentration was 25 times higher and the particle concentration was three times higher in the effluent compared to the receiving body of water. This indicates that WWTPs may operate as a route for microplastics entering the sea.

Activated carbon (AC) is an effective adsorbent in water treatment but its production method has significant emissions to the environment. This study aims to quantify the environmental impacts of various AC types and determine whether raw material selection could reduce the footprint of AC. A cradle-to-gate life cycle assessment (LCA) was conducted on coal, coconut shell, wood, peat, and reactivated coal ACs. The different types of raw materials were selected to reflect typical global and local availability in the selected location. Life cycle data was collected from the Ecoinvent database, scientific literature, and an industrial producer. Using CML 2001 as a characterization method, potential environmental impacts were calculated for 12 categories. The direct emissions of AC production and electricity production were the largest contributors to environmental impacts. Coal AC had the highest impact in ten out of the twelve categories. On the other hand, reactivated coal and coconut AC had the lowest impacts in three and five categories, respectively. The comparison in carbon footprints between the AC types were found to be dependent on inclusion or exclusion of biogenic emissions: When including biogenic carbon emissions, the Global Warming Potential (GWP) of reactivated coal AC was 72-80% lower than for the virgin ACs. When biogenic carbon emissions were excluded, the GWPs of the residual biomass ACs (coconut shell and wood) were found to be about 50% lower than that of reactivated coal AC. The results demonstrate that raw material choice and production method significantly affect the environmental impact of AC. To minimize site-specific impacts of AC application, technical feasibility of AC and use phase emissions need to be assessed.