Abstract
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.
Highlights
Nutrient recovery is one of the key drivers promoting sustainability in wastewater management and the circular economy (Hoffmann et al, 2020; Larsen et al, 2021a)
This can potentially increase the social acceptance of wastewater-based nutrients in agriculture, the presence of pharmaceuticals and hormones are often regarded as limiting factors, even though it has been suggested that they are likely to be degraded during the growing season (Viskari et al, 2018)
This study showed that in sparsely populated areas such as northern Finland and Sweden, implementing source separation both in rural and peri-urban areas would significantly increase the potential for nutrient recovery from wastewaters and reduce the overall climate and eutrophication impact of wastewater management, but lead to increase in acidification
Summary
Nutrient recovery is one of the key drivers promoting sustainability in wastewater management and the circular economy (Hoffmann et al, 2020; Larsen et al, 2021a). Wastewater contains, among other substances, phosphorus and nitrogen, which are vital nutrients for food production. Current practices in wastewater management lead to inefficient recovery and reuse of wastewater-based nutrients and can result in environmental problems such as eutrophication, contribute to climate change, and undermine global food security (Kjerstadius et al, 2017; Skambraks et al, 2017; Wielemaker et al, 2018; Hoffmann et al, 2020; Öberg et al, 2020). The production of nitrogen fertilizers is responsible for about 0.8% of global greenhouse gas emissions due to its high energy consumption (Brentrup, 2009)
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