The effectiveness of nature-based hybrid solutions for the removal of nitrogen and emergent pollutants from municipal wastewater in cold climate conditions

Arctic aquatic environments are especially sensitive to nutrient (nitrogen and phosphorous) and emergent pollutant discharge, which commonly enters water systems through wastewater effluents. To remove nutrients and emergent pollutants from the municipal wastewater in a small village in northern Finland, we evaluated a hybrid nature-based treatment system designed to complement an existing conventional wastewater treatment facility. The system included a moving bed bioreactor installed within the existing facility to improve nitrification; a sedimentation basin, moss unit, fungi-woodchip unit, and two woodchip bioreactors were also placed in the former drainage ditch after the facility to increase nutrient and emergent pollution removal. System performance was monitored for 5 years across all seasons to assess treatment efficiency. The treatment facility went from leaching of total nitrogen prior to implementation of the hybrid system to an average of 31 % removal efficiency after the system was implemented. Of the 129 emergent pollutants analyzed, 58 were below the detection limit, 20 showed no removal through the treatment process, and 51 compounds showed changes in concentration throughout the hybrid treatment system. Of the 51 compounds which showed changes in the system, 20 showed clear removal trends throughout the entire hybrid treatment system (normal wastewater treatment system + moss and fungi units and woodchip bioreactors), and 8 showed clear removal only in the woodchip bioreactor. Temperature did not appear to have a noticeable impact on the removal efficiency of these compounds. In view of the findings of this study, future research should be directed at further system optimization (in this case by better optimizing the MBBR), increasing, if possible, the number of sampling times and points for the emergent pollutants, and investigating in more detail the interaction between microbes and pollutant removal in cold climatic conditions.