Current practices in wastewater management lead to inefficient recovery and reuse of nutrients and can result in environmental problems. Source separation systems have been shown to be an efficient way of recovering nutrients and energy from wastewaters, both in rural and urban context. Studies on nutrient recovery potential and life cycle impacts of source separation systems are mainly limited to small systems (for example a few households) while the impacts of upscaling source separation to a regional level have hardly been studied, especially in sparsely populated areas where the cost of the connection to a main treatment plant is higher. This study examines the regional nutrient balance of two source separation scenarios—black water separation and urine diversion—and compares them to the existing conventional wastewater system. The analysis comprises three sparsely populated regions of northern Finland and Sweden, including rural, peri-urban and urban areas. In addition, climate impacts are assessed based on existing life cycle assessment (LCA) studies. According to the results, by source separation it is possible to achieve a significant increase in the recovery rate of phosphorus (41–81%) and nitrogen (689–864%) compared to the conventional system. Depending on the region up to 65% of the mineral phosphorus and 60% of mineral nitrogen fertilisers could be theoretically replaced. Furthermore, the climate and eutrophication impacts would decrease with the implementation of such systems, but an increase in acidification may occur. However, even if the benefits of source separation systems are undisputed in terms of nutrient recovery, the implementation of such systems would to a large extent require an entire system change of the wastewater treatment sector and a wide paradigm change towards a circular economy.

In this study, life cycle assessment (LCA) and life cycle costing (LCC) methods were applied for the new city district of Hiedanranta, where source-separating sanitation systems are being considered. Two source-separating systems were compared to the conventional sanitation system with a centralized wastewater treatment plant (WWTP). With a separating system, three to 10 times more nitrogen could be recovered compared to the conventional system. If the nutrient potential of the reject water of the sludge digestion were to be utilized, the recovery rate would be even higher. For phosphorus, the recovered amount would be at the same level for all the alternatives. However, the plant availability of phosphorus is higher in separating systems. Based on the environmental impacts of separating systems with improved nutrient recovery, the climate and eutrophication impacts could be reduced, but the acidification impact may be higher. However, the actual climate benefits depend on how the avoided emissions will be realized, which is highly dependent on the policy and decision-making processes in the society. The life cycle costs of the alternative source-separating systems are higher at current prices. Source-separating sanitation produces new recycled nutrient products of human origin that contain fewer contaminants and could therefore be more easily accepted for end use when certain boundary conditions are met.

Biogas production is seen as one of the key measures in circular economy providing several benefits for the environment. In practice, however, these benefits may not be achieved if the production is not implemented and managed in ways that reduce gaseous emissions. Thus, this study aimed at highlighting how different management practices impact the climate during the life cycle of biogas production in comparison to management without biogas production (reference). Advanced, more emission-reducing practices resulted in 97-107% and conventional practices in 57-75% less emissions when biogas was utilized as transport fuel. If biogas was utilized in CHP (combined heat and power production), the emission reductions were 67-74% and 13-30%, respectively. This reflects the fact that inefficient practices can lead to minimal emission reduction without achieving the desired climate benefit in comparison to the reference. On the European level, this may also mean that the emission reduction demands of RED II (Renewable Energy Directive) regulation are not met. Therefore, when supporting biogas production with public funds, assurance of using emission-reducing practices should be made a prerequisite.

Sewage sludge monitoring data on many harmful organic pollutants is scarce. In this study, 23 contaminants of environmental concern were identified, including: Per- and polyfluoroalkyl substances (PFAS), pharmaceuticals and personal care products, hormones, and flame retardants. First, concentration data in sludge from the Nordic countries, was compiled. Several data gaps on concentration data were found, particularly in personal care products and flame retardants groups. There were also large differences in data availability between the countries. Second, removal efficiency of the selected pollutants was reviewed. Three different treatment methods were considered: anaerobic digestion, composting, and pyrolysis. Pyrolysis emerged generally as the most efficient removal method, whereas there were large differences in the reported removal efficiencies in anaerobic digestion and composting. Overall, the most recalcitrant pollutants in sludge in this study were PFAS, certain antibiotics, and estrogens. Several factors behind the variation were identified, such as diversity in plant design, operational and seasonal parameters, and challenges in sampling and analysing the sludge matrix. Coherent study designs are needed to compare removal efficiencies more transparently. Legislative requirements are usually the main drivers for carrying out monitoring, andurrent EU legislation regulating hazardous substances in sewage sludge is outdated. There is great variation in national regulations between the Nordic countries. The lack of regulatory requirements hinders informed/science-based long-term decision-making to protect the environment. Sludge utilization is a complex question requiring consideration from regulative, technological, and societal perspectives. Monitoring contaminants is vital in both assessing risks of sludge-based fertilizers and contaminant removal efficiencies in sludge treatment.