The Baltic Sea is particularly vulnerable to waterborne nutrient loadings because of its large catchment in relation to the sea area, a long renewal time and limited water exchange with the North Sea. The ecological status of the open water in the Baltic Sea is poor and affected by eutrophication [1]. The spatial extent of open water eutrophication in the Baltic Sea has increased in recent years [2], despite measures to decrease emissions. The primary cause of eutrophication is increased primary production as a result of increased loading of inorganic nutrients from terrestrial sources, followed by an increase in organic matter loading [1].
The major sources of nutrient emissions to the Baltic Sea are diffuse, mostly agricultural, followed by point sources, mostly from municipal wastewater treatment plants [3]. Both nitrogen and phosphorous biogeochemical cycles are considered planetary boundaries, within which humans can be safely sustained by the earth systems [4]. The global nitrogen cycle has severely overstepped its threshold, and fixation of nitrogen from the atmosphere should be reduced [4, 5]. Additionally, fixation of atmospheric nitrogen by the Haber–Bosch process to produce nitrogen fertilizer is very energy consuming, leading to fossil fuel originated emissions [6]. Phosphorus, naturally occurring in the earths’ crust, is a non-renewable resource on its way to depletion [4]. The European Commission has identified phosphate rock and phosphorus as critical raw materials with high economic importance and supply-risk [7].
Cornejo et al. [8] found that nutrient recovery from wastewater can, by substituting mineral fertilizers, reduce the eutrophication potential by up to 8% and total carbon footprint by up to 4%, depending on the size of the treatment plant. The study also showed that by integrating recovery of water, nutrients and energy the eutrophication potential could decrease by 18% and carbon footprint by 34% when treating wastewater from 100,000 people [8]. Recycled nutrients from waste and wastewater could substitute mineral nitrogen and phosphorous fertilizers in agriculture. There are also other uses for nutrients in industry and other resources in waste that could be utilized. For example, Mihelcic et al. [9] estimated, based on data for the year 2009, that phosphorus in the excreta of the whole human population could satisfy 22% of global phosphorous demand.
Utilizing resources in waste is a sustainable practice and central in a circular economy [10]. The wastewater treatment of today could provide multiple benefits to society if integrated with resource recovery [11]. There exists a number of technologies to recover nutrients, and other resources, from wastewater. There is a growing interest in recovering resources, such as energy and plant nutrients, from wastewater. The conventional treatment of wastewater is focused on the removal of nutrients and carbon, but it seems to be shifting towards recovery [12, 13]. However, there is no systematic overview of the literature on technologies to recover nutrients and carbon from wastewater sources done to date.
In order to focus the study, the concept of ecotechnology was used. The term ‘ecotechnology’ describes combinations of practices relating to the environment and technical innovation. It has been used since the early 1970s, but a recent systematic review and thematic synthesis of the research literature shows it has been used as a buzzword with few explicit definitions [14]. We have based our definition of ecotechnology on theirs:
“Eco-technologies are human interventions in social-ecological systems in the form of practices and/or biological, physical, and chemical processes designed to minimise harm to the environment and provide services of value to society” [14]
We use this broad definition, which encompasses both technologies and practices, so as to remain conservative and broadly relevant. For this map, we add on to the definition that the ecotechnologies should be related to wastewater management and facilitate the reuse of carbon and/or nutrients.
