Restoring nutrient circularity across scales is important for ecosystem integrity as well as nutrient and food security. As such, research and development of technologies to recover plant nutrients from various organic residues has intensified. Yet, this emerging field is diverse and difficult to navigate, especially for newcomers. As an increasing number of actors search for circular solutions to nutrient management, there is a need to simplify access to the latest knowledge. Since the majority of nutrients entering urban areas end up in human excreta, we have chosen to focus on human excreta and domestic wastewater. Through systematic mapping with stakeholder engagement, we compiled and consolidated available evidence from research and practice. In this paper, we present ‘Egestabase’ – a carefully curated open-access online evidence platform that presents this evidence base in a systematic and accessible manner. We hope that this online evidence platform helps a variety of actors to navigate evidence on circular nutrient solutions for human excreta and domestic wastewater with ease and keep track of new findings. 

Ecotechnologies have the potential to reduce the use of finite resources while providing a variety of co-benefits to society, though they often lack in market competitiveness. In this study, we investigate the sustainability of ecotechnologies for recovering carbon and nutrients, and demonstrate how a so-called “bottom-up” approach can serve as a decision-making instrument. Based on three case study catchments with a focus on domestic wastewater in Sweden and Poland, and on manure, grass and blackwater substrates in Finland, we apply a cost–benefit analysis (CBA) on system alternatives derived from a participatory process. After drawing on an initial systematic mapping of relevant ecotechnologies, the scope of the CBA is determined by stakeholder suggestions, namely in terms of the considered assessment criteria, the physical impacts and the utilised data. Thus, this CBA is rooted in a localised consideration of ecotechnologies rather than a centralised governmental approach to systems boundaries. The key advantage of applying such a bottom-up approach is that it has gone through a robust participatory selection process by local stakeholders, which provides more legitimacy to the decisions reached compared with traditional feasibility studies. Despite considering the revenues of the recovered products as well as the provision of the non-market goods CO2 mitigation and reduced eutrophication, findings from this study indicate that the benefits of the considered ecotechnologies are often outweighed by their costs. Only anaerobic digestion of agricultural wastes appears to be economically feasible under the current conditions, highlighting that further efforts and incentives may be required to mainstream ecotechnologies. © 2021, The Author(s), 

There exist numerous ecotechnologies for recovery and reuse of carbon and nutrients from various waste streams before they are lost to runoff. However, it remains largely unknown how growing implementation of such ecotechnologies affect nutrient emissions to surface waters at catchment scale. Here, this knowledge gap is addressed by application of SWAT model in three case study catchments draining to the Baltic Sea: Vantaanjoki (Finland), Fyrisån (Sweden) and Słupia (Poland). Sustainability analysis with Multi-Criteria Analysis was applied in the stakeholder workshops in the case study areas to assess different ecotechnology alternatives. The following ecotechnologies received the highest sustainability scores: in Vantaanjoki anaerobic digestion, based on mostly agricultural residues; in Fyrisån source-separation of wastewaters; in Słupia nutrient extraction within the wastewater treatment process. The effect of application of digestate on agricultural soils in the Vantaanjoki catchment was simulated by adjusting the model parameters describing the organic carbon content and physical properties of soil. The results showed small reductions of nutrient loads to the Gulf of Finland. Larger reductions of nutrient loads to Lake Mälaren in Sweden and the Baltic Sea in Poland were achieved as a result of the wastewater treatment upgrades. In the Fyrisån catchment, higher relative reductions were simulated for TN than TP, and in dry years than in wet years. Although the studied ecotechnologies did not show as high effectiveness in nutrient load reduction as combinations of traditional Best Management Practices reported in literature, they do have other multiple benefits including crop yield increase, electricity, heat and bio-based fertilizer production.

Research and Innovation Agenda for Recovery of Nutrients from Wastewater

Projects funded on the topic of nutrient recovery and reuse in Sweden over the past years have been scattered, lacking a coherence in direction and coordination between the numerous research funding organizations. This agenda has been developed with the purpose of creating a framework and common understanding of what research and innovation is necessary to move forward in a transition to a circular nutrient economy. The goal was to identify and prioritize the R&I needs in order to enable a productive dialogue between investors, researchers and other crucial societal actors including organizations, the public sector and the industry.

The results and conclusions presented in this report are mainly drawn from a workshop in September 2019, with around 40 participants representing the water and wastewater sector, municipalities, academia, the agricultural sector, the industry and Swedish national agencies.

In the transition to a more circular management of nutrients including waste streams, several challenges were identified. The identified challenges in a nutshell:

- Current system solutions are not optimized, there is a lack of holistic approach- Business models and incentives to choose products based on recovered nutrients on the market are missing- Technology needed for circular management of nutrients are in general on a low technology readiness level- Recovered nutrient products must maintain a uniform and high quality in order to compete on the market and the requirements should be the same for all fertilizers.

The agenda concludes that the research and innovation actions to meet the challenges should follow a holistic approach that includes the entire value chain of nutrient management in the food system. All essential nutrients in the food system and other resources in its waste streams should be considered, to maximize efficient and circular nutrient management. Based on this understanding, that a holistic approach is of such importance to target the identified challenges, the research and innovation needs were identified as:

- Develop a national plant nutrient management strategy that describes holistically how to manage nutrients overall in a circular economy- Develop goals and targets for nutrient recovery from wastewater based on this nutrient management strategy (the Swedish inquiry on sludge management suggested a requirement of 60 % phosphorus recovery from wastewater treatment plants, this should just be the beginning and goals should also be set for other nutrients)- A larger interdisciplinary R&I effort regarding the recovery goals should be coordinated to analyze how the transition to a circular management of nutrients best can be accomplished on a systems level- Provide support to develop business models for optimal collaboration between different actors in different parts of the value chain and maximized resource efficiency- Technology development and demonstrations aligned with the holistic approach for circular management of nutrients in the suggested national nutrient management strategy

The Swedish project P-to-Product focused on developing and adapting methods to promote recirculation of phosphorus (P) products extracted from sewage and sewage sludge. The project consisted of three work packages: 1) market introduction, 2) environmental impacts and 3) agricultural requirements. In wp 1 opportunities and barriers were identified and policy recommendations developed. This was done through interviews, surveys and workshops with stakeholders from sewage utilities, innovation companies, the fertilizer industry, the federation of Swedish farmers and national authorities. In wp 2 a simplified Life Cycle Assessment (LCA) was developed focused on nutrient recycling, global warming potential and energy use. In addition to this a chemical checkpoint was formulated with chemical analysis of a wide range of pollutants. For the development of methods in wp 2, granulated or pelleted nutrient products from the companies EkoBalans (a struvite based product with nitrogen and potassium added) and Outotec (a P-product with origin from incinerated sewage sludge) were used as case products. These products were also used in wp 3 where physical properties were evaluated and spreading tests were executed using existing machinery. The project provided a useful set of methods which soon will be complemented with methods to assess plant nutrient efficiency.

Small on-site sanitation systems are widely present in suburban and rural areas in many countries. As these systems often underperform and have an impact on receiving waters, understanding their overall sustainability is of interest for policy and decision-makers. However, the definition and estimation of indicators defining sustainability are challenging, as it is finding the methodological approach to combine qualitative and quantitative indicators into one comprehensive assessment. In this study, twelve indicators defined by environmental, economic, social, technical and health-related criteria were used to compare nine alternatives of on-site sanitation for single households. A non-compensatory method for multi-criteria decision analysis, ELECTRE III, was used for the assessment together with weights assigned to each indicator by a reference group. Several scenarios were developed to reflect different goals and a sensitivity analysis was conducted. Overall, the graywater-blackwater separation system resulted as the most sustainable option and, in terms of polishing steps for phosphorus removal, chemical treatment was preferred over the phosphorus filter, both options being implemented together with sand filters. Assessing the robustness of the systems was a crucial step in the analysis given the high importance assigned to the aforementioned indicator by the stakeholders, thus the assessment method must be justified. The proposed multi-criteria approach contributes to aid the assessment of complex information needed in the selection of sustainable sanitation systems and in the provision of informed preferences. © 2019 The Royal Society of Chemistry.

The purpose of this study was to compare the energy use and climate impact of extracting phosphorus (P) from sewage sludge, compared with mineral phosphorus from mining. The two processes that are studied are struvite precipitation and extraction of phosphorus from sludge ash (AshDec). We also looked at the potential recycling rate of plant nutrients in the different systems.

In the study, we have calculated the environmental impact of introducing the processes for P-recovery, related to a conventional sewage treatment plant with chemical precipitation. It is therefore only the differences that arise in comparison with the reference plant that are included in the calculations. You can think like this: there is an existing sewage treatment plant, where you introduce P recycling. All changes in environmental impact that arise in connection with the investment in this new process are burdens the new P-product.

The results show that the AshDec scenario has the best recovery rate of phosphorus and energy balance, while the struvite scenario shows the best return rate of nitrogen and the lowest climate impact. However, the sensitivity analyzes show that the results are strongly influenced by different assumptions. For the AshDec scenario, assumption about nitrous oxide emissions from incineration of sludge as well as the handling of energy surplus is crucial. For the struvite scenario, assumptions around the reconstruction of the sewage treatment plant to biological phosphor cleaning is of great significance, especially if the biogas production is affected.

This report is written within the framework of the state's public inquiries M 2018:08, committee directive 2018:67 "Non-toxic and circular recycling of phosphorus from sewage sludge". One of the tasks in the directive is a task about mapping the technological development for phosphorus recovery, which this report highlights.

The methodology for answering the question has been to examine scientific articles published in recent years, and to review documentation from recent years' conferences, seminars and EU projects (completed and ongoing) in the field. Among the sources available on the internet, the German, Swiss and European phosphorus platforms have been the most important. A selection has been made of relevant processes, where the selection criteria are reported in the report. The starting point for recovering phosphorus is inside the waste water treatment plant (WWTP) where the sludge occurs. The reported processes have been subdivided on the basis of where in the process scheme they have their starting point, which is also the most common classification according to the literature.

The result is that the choice of method must be a balance of what one wants to achieve because no method meets all the wishes. A vast majority of processes meet the criterion of depollution, ie the degree of detoxification is very high, which is an important driving force for introducing them. The recycling potential of the processes is very variable, from 20 % of incoming phosphorus to the WWTP (usually struvite processes etc.) to just over 95 % of incoming phosphorus (usually thermal processes, e.g. biokol and extraction from ash), since it involves the whole sludge stream. In order to achieve a high recovery rate when internal processes are applied, it is also required that the phosphorus in the remaining dewatered sludge is recycled.

Only one category of processes is assessed to be fully developed, namely the struvite processes. All other processes are considered "new technology" or "promising innovations". Most of the internal processes in WWTP do not fit well in Sweden because most Swedish WWTPs use chemical precipitation of phosphorus instead of biologically.

An important aspect from the system- and economic point of view is in what form the phosphorus comes out of the process, which is highly variable for the processes studied. The processes in which phosphorus comes out in a form known to the agriculture (or industry) are considered to have the greatest potential to be viable in the long term. It has been difficult to obtain costs for introducing the studied processes, this because the processes are under development. It is often pointed out that phosphorus recovery processes are very expensive, but compared to today's costs that WWTPs has to get rid of the sludge, it is unclear how large the cost difference actually becomes.

The report also highlights the environmental impacts from a life-cycle perspective. The general conclusion is that it is difficult to obtain knowledge because most of the processes are under development, and that it is difficult to draw any clear results from the analyzes that have been fulfilled.

Three different ways of taking care of the entire sludge flow have been identified; bio-coal, ash and ash extraction. The first means that the entire sludge amount is dried and pyrolyzed and the remainder is a bio char which should be regarded as a carbon-sink and a long-term phosphorus source. The second way is to burn ash and direct spread of this ash. The third way involves the extraction of phosphorus from this ash in different ways and here there are three methods of this type that are at approximately the same level of development. Two other methods that are regarded as promising innovations are about HTC processes (hydrothermal carbonization) and extraction using CO2. Assessed advantages and disadvantages for these and other categories of processes can be found in the report.