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• Cities benefit from nutrient circularity integrating waste and local agriculture. • Significant benefits from biogas generation and avoiding mixed waste treatment. • Nutrient concentrations in urban agricultural soils limit application of compost. • Local regulations and soil quality hinder nutrient circularity in urban areas. Cities face the challenges of supplying food and managing organic municipal solid waste (OMSW) sustainably amid increasing urbanization rates. Urban agriculture (UA) can help with this effort by producing local crops that are fertilized with nutrients recovered from compost generated from OMSW. This research aims to determine the potential of OMSW compost to supply the nitrogen-phosphorus-potassium (NPK) demand of UA and the environmental benefits of replacing mineral fertilizer from a life cycle perspective. The Metropolitan Area of Barcelona (AMB) serves as the case study given its commitment to reuse biowaste according to the Revised Waste Framework Directive and to promote UA as a signing member of the Milan Urban Food Policy Pact. Based on crop requirements and farmer surveys, we find that the annual NPK demands of the agricultural fields of the AMB that cover 5,500 ha and produce 70,000 tons of crops are approximately 769, 113, and 592 tons of NPK, respectively. Spatial material flow analysis and life cycle assessment were applied to found that the current waste management system can potentially substitute 8 % of the total NPK demanded by UA with compost, reduce the impacts by up to 39 % and yield savings in global warming of 130 %. The more ambitious future scenario of 2025 can potentially substitute 21 % of the total NPK demand and reduce environmental impacts up to 1,049 %, depending on the category considered. Avoiding processing of mixed OMSW, mineral fertilizer replacement and cogeneration of electricity from biogas are the major contributors to these environmental savings. [ABSTRACT FROM AUTHOR]

Sustainable management of lakes requires us to overcome ecological, economic, and social challenges. These challenges can be addressed by focusing on achieving ecological improvement within a multifaceted, co-beneficial context. In-lake restoration measures may promote more rapid ecosystem responses than is feasible with catchment measures alone, even if multiple interventions are needed. In particular, we identify restoration methods that support the overarching societal target of a circular economy through the use of nutrients, sediments, or biomass that are removed from a lake, in agriculture, as food, or for biogas production. In this emerging field of sustainable restoration techniques, we show examples, discuss benefits and pitfalls, and flag areas for further research and development. Each lake should be assessed individually to ensure that restoration approaches will effectively address lake-specific problems, do not harm the target lake or downstream ecosystems, are cost-effective, promote delivery of valuable ecosystem services, minimize conflicts in public interests, and eliminate the necessity for repeated interventions. Achieving optimal, sustainable results from lake restoration relies on multidisciplinary research and close interactions between environmental, social, political, and economic sectors. This article is categorized under: Science of Water > Water Quality Water and Life > Stresses and Pressures on Ecosystems Water and Life > Conservation, Management, and Awareness [ABSTRACT FROM AUTHOR]

Policymakers and researchers have discussed mission-oriented innovation policies (MIPs) as one way to tackle the grand challenges of modern societies. Our contribution to MIP research is to provide a case analysis of the unfolding of such a policy from a hybridity perspective. Hybridity refers to the amalgamation of public policies, private efforts, and voluntary activities when pursuing societal aims. In practice, hybridity integrates value propositions from governments, markets, and civil society. Our case study subject is the Finnish nutrient recycling (NR) policy. The NR policy aims to supersede the dominance of chemical fertilisers with organic fertilisers. We analysed forms of hybridity and hybrid constellations of actors that were initiated as part of the Finnish NR policy. Subsequently, we analysed how the value-creation mechanisms of legitimising, compromising, and mixing appear in the NR policy. As a result, we conceptualised what the process of hybridisation entails in the context of MIPs. [ABSTRACT FROM AUTHOR]

The evolution of environmental policy is increasingly driven by the emergence and interaction of policy concepts and the frameworks, knowledge, and ideas they employ. We argue that policy actors' creative use of policy concepts often leads to their combinatorial development. In this policy process, the concepts interact and shape each other's policy relevance and future development under the influence of ideas, knowledge, and political factors. We formulate this new research approach using ideational and policy process theories. In particular, we explicate internal and contextual combinatory elements that enable policy change resulting from mutual development of policy concepts. For an empirical demonstration, we analyze the conceptual innovation, rise, and ramifications of nutrient recycling as a new segment of Finnish environmental policy. [ABSTRACT FROM AUTHOR]

Aquaculture has grown rapidly to play a crucial economic and social role and meet the increasing global demand for seafood. As aquaculture intensifies, there is increasing pressure to find more sustainable practices that save resources and reduce waste. Major wastes and by-products from aquaculture were quantified across a full range of farming types. Key opportunities for wastewater treatment and by-product recovery include nutrient recycling through a combination of biofilters, bioaccumulation and multitrophic systems. To support a sustainable intensification of aquaculture, improvements in by-product harvesting, accumulation and processing methods require further investigation. Likewise, energy generated from by-products can potentially support intensified production through land-based recirculating aquaculture systems (RAS). Future challenges faced by the reuse of side streams include control of food safety and gaining consumer acceptance. Combined with increases in resource use efficiency across the aquaculture sector, from feeding methodologies to product storage, nutrient recycling can enable aquaculture to contribute sustainably toward the nutritional requirements of billions of people over the next century. [ABSTRACT FROM AUTHOR]

[Display omitted] • Sewage sludge can be used as substitute for conventional fertilizer resources; • Organo-mineral fertilizers optimized for maize and sunflower crops were produced; • The share of waste materials in organo-mineral fertilizers was 49–54%; • Fertilizer production based on waste allows for organic matter and nutrient recycling. The depletion of natural resources, energy consumption and environmental issues relating to fertilizer production processes are driving a move towards a more sustainable use of resources and the recycling of nutrients. With regard to the fertilizer industry, this gives the opportunity to use the fertilizing potential of alternative raw materials. This paper evaluates the possibility of using dried sewage sludge in the manufacture of organo-mineral fertilizers. Fertilizers based on sewage sludge with an addition of poultry litter ash and mineral fertilizers were developed and characterized in the study. It was possible to produce multicomponent organo-mineral fertilizers with optimized compositions for maize and sunflower crops, characterized by total nutrient content over 20%. Moreover, they contained beneficial secondary nutrients and micronutrients originated from waste materials. The fertilizers were free of pathogens and fulfilled the requirements related to heavy metal content according to Polish legislation. The method of manufacturing organo-mineral fertilizers based on waste materials is a simple waste management solution offering organic matter and nutrient recycling in line with the circular economy and reducing reliance on imported raw materials. [ABSTRACT FROM AUTHOR]

The circular economy (CE) is currently generating considerable expectations. The concept describes an aspired future but does not provide clear guidance for policy-making. As policy outcomes often rest on initiatives generated in a bottom-up fashion, our attention must be directed to the ways policies are made accessible and interesting to those who might take the initiative. We claim that on-line publicity plays a key role in this. Our findings from a hyperlink analysis focusing on a government funding call for nutrient recycling in Finland show how multiple versions of the policy topic unfold online, as emergent hyperlink clusters prioritize specific agents, material circuits, and policy visions over others. The topic becomes connected with activities and agendas to create path dependencies and to strengthen existing divisions rather than to advocate change. Thus, we argue that CE policy design must recognize the way policy is shaped through online publicity creation. [ABSTRACT FROM AUTHOR]

The circular bio-based economy offers great untapped potential for the food industry as possible valuable products and energy can be recovered from food waste. This can promote more sustainable and resilient food systems in Europe in follow-up of the European Commission's Farm to Fork strategy and support the global transition to more sustainable agri-food systems with the common agricultural and fisheries policies. With its high nutrient content, waste and by-products originating from fish and seafood industry (including aquaculture) are one of the most promising candidates to produce alternative fertilising products which can play a crucial role to replace synthetic mineral fertilisers. Whereas several studies highlighted the opportunities to recover valuable compounds from fishery waste, study towards their potential for the production of fertilising products is still scarce. This study presents an extensive overview of the characteristics of fishery waste and by-products (i.e., fish processing waste, fish sludge, seafood waste/by-products), the state-of-the-art nutrient recovery technologies and recovered nutrients as fertilising products from these waste streams. The European Commission has already adopted a revised Fertilising Products Regulation (EU) 2019/1009 providing opportunities for fertilising products from various bio-based origins. In frame of this opportunity, we address the quality and safety aspects of the fishery waste-derived fertilising products under these criteria and highlight possible obstacles on their way to the market in the future. Considering its high nutrient content and vast abundance, fish sludge has a great potential but should be treated/refined before being applied to soil. In addition to the parameters currently regulated, it is crucial to consider the salinity levels of such fertilising products as well as the possible presence of other micropollutants especially microplastics to warrant their safe use in agriculture. The agronomic performance of fishery waste-derived fertilisers is also compiled and reported in the last section of this review paper, which in most cases perform equally to that of conventional synthetic fertilisers. • Fish processing waste/wastewater/sludge has high protein and lipid contents. • The choice of technology depends on the raw material and desired end-product. • Salinity and microplastics are potential critical parameters. • Fish sludge has a great potential but should be treated/refined before application. • Fishery waste-based fertilisers perform equally to commercial synthetic fertilisers. [ABSTRACT FROM AUTHOR]

Carbon emissions and associated global warming have become a threat to the world, the major contributor being the extensive use of fossil fuels and uncontrolled generation of solid wastes. Energy generation from renewable energy sources is considered an alternative to achieving carbon neutrality. Anaerobic digestion (AD) is a sustainable technology that has been endorsed as a low-carbon technology complimenting both waste management and renewable energy sectors. The AD technology recovers the volatile matter from waste biomass as much as possible to produce biogas, thus reducing carbon emission as compared to open dumping or burning. However, there is a need of compilation of information on how each subsystem in AD contributes to the overall carbon neutrality of the entire system and chances of achieving a circular economy along with it. Therefore, this article aims to clarify the associated internal and external factors that determine the low carbon characteristic of anaerobic digestion technology. From this review, the potential of AD system for energy-atmosphere-agriculture nexus has been explored. Carbon emission mapping of the potential entities involved in AD were identified and perspective to life cycle assessment and future research direction has been pointed out. Climate change impact and acidification potential are the two entities that can influence the overall environmental sustainability of an AD system. It was recognized that each stage of AD system starting from substrate supply chain, biogas production, upgradation, utilization, and digestate application had a remarkable effect on the overall carbon emission potential based on its design, operation, and maintenance. Selection of suitable substrates and co-digesting them together for improved biogas production rate with high methane content and proper digestate post-processing and storage can vastly reduce the carbon emission potential of the AD technology. Further, a case scenario of India was assessed considering the utilization of major surplus biomass available through AD. Re-routing the three major substrates such as agricultural crop residues, animal wastes and organic fraction of municipal solid wastes through AD can reduce at least 3.5–3.8 kg CO 2-eq per capita of annual carbon emission load in India. Furthermore, the pathways in which the policy and legislations over establishment of AD technology and how to explore linkages between achieving circular economy and low carbon economy for Indian scenario has been highlighted. • The carbon recovery potential of anaerobic digestion (AD) technology is reviewed. • The benefits of AD for energy-agriculture-atmosphere nexus are discussed. • Coverage area and digestate handling segments significantly influences the low carbon nature of AD. • With the current research, AD has the potential to reduce up to 4 kg per capita of CO2-eq. • The role of AD for creating a low carbon circular economy model is highlighted. [ABSTRACT FROM AUTHOR]

Managing organic waste streams is a major challenge for the agricultural industry. Anaerobic digestion (AD) of organic wastes is a preferred option in the waste management hierarchy, as this process can generate renewable energy, reduce emissions from waste storage, and produce fertiliser material. However, Nitrate Vulnerable Zone legislation and seasonal restrictions can limit the use of digestate on agricultural land. In this paper we demonstrate the potential of cultivating microalgae on digestate as a feedstock, either directly after dilution, or indirectly from effluent remaining after biofertiliser extraction. Resultant microalgal biomass can then be used to produce livestock feed, biofuel or for higher value bio-products. The approach could mitigate for possible regional excesses, and substitute conventional high-impact products with bio-resources, enhancing sustainability within a circular economy. Recycling nutrients from digestate with algal technology is at an early stage. We present and discuss challenges and opportunities associated with developing this new technology. [ABSTRACT FROM AUTHOR]

The polychaete Hediste diversicolor is known to recycle side streams from aquaculture and biogas production. We conducted a feeding experiment to evaluate whether rearing temperature or mixtures of these two side streams enhances biomass production and fatty acid composition. We reared H. diversicolor along a 5-temperature gradient ranging from 5.8 °C to 17.1 °C and a 4-step gradient form 100% aquaculture sludge to 100% solid biogas digestate. Formulated fish feed served as a control diet. Polychaetes increased growth rate with increasing temperature, ranging from 0.01 at 5.8 °C to 0.14 at 17.1 °C, while survival was inversely affected by temperature with 100% survival at 5.8 °C and 70% survival at 17.1 °C. Diet had a less pronounced effect on polychaete survival, and no significant effect on growth rates. Contrasting to growth, the fatty acid composition of the polychaetes was not affected by temperature but was highly influenced by diet, as polychaetes did not cluster by rearing temperature but by the diets they received. In conclusion, H. diversicolor can be utilized as a recycler of aquaculture and biogas side streams, and production temperature can be optimized for growth without compromising fatty acid composition and quality of the polychaetes. • We cultivated polychaetes along a temperature and food quality gradientby mixing aquaculture sludge and biogas digestate • Temperature had a significant effect on growth and survival of the polychaetes but not on fatty acid profiles • Diet had a pronounced effect on fatty acid composition of the polychaetes, but not on their growth and survival • We found an absence of homeoviscous adaptation in H. diversicolor • Cultivation temperature can be optimized for polychaete growth rates without compromising their nutritional value. [ABSTRACT FROM AUTHOR]

Boron (B) fertilizers are essential for global crop production. Sustainable B use demands a higher efficiency of B fertilizers through controlled B release and an enhanced B recycling from secondary sources, e.g. B-impregnated cellulose fiber insulation (CFI) waste. In this study, thermochemical treatments based on combustion and pyrolysis were investigated for processing CFI waste into a slow-release B fertilizer. Hot-water extractions of obtained materials confirmed that slow-release properties were achieved, and material characterization with XRD, FTIR and 11B-NMR showed that these were largely the result of formation of sparingly soluble Ca–B phases. A seedling toxicity test with fodder rape demonstrated the benefit of this slow-release B in comparison with conventional soluble B to circumvent toxicity, suggesting potential for B application via seed coatings. Finally, a fertilization trial with fodder rape and poppy seed showed that most slow-release B compounds were equally effective as soluble B at recommended B doses, while slow-release B can still benefit from reduced B leaching losses. [Display omitted] • Thermochemical processing of B-rich cellulose fiber insulation (CFI) was tested. • Obtained combustion and pyrolysis products had slow-release B characteristics. • Slow-release B was largely the result of formation of sparingly-soluble Ca–B phases. • B toxicity to plants could be avoided using treated CFI instead of soluble B. • In a plant fertilization trial, treated CFI was equally effective as soluble B. [ABSTRACT FROM AUTHOR]

Cycling of nutrients, such as phosphorus (P) and nitrogen (N), is essential for all life: Nutrients are crucial for securing societies' food systems and valuable raw materials for industrial processes. Recycling nutrients from various side and waste streams instead of virgin nutrients has attracted considerable interest in the society, particularly as geopolitical and epidemic issues have caused many nations to reconsider how they ensure flows of critical resources by increasing the Circular Economy (CE) principles. This study examines what drivers and barriers catalyze nutrient circulation in national settings, requiring diverse actors to support intentional nutrient recycling. By taking multidisciplinary and ecosystem approaches, we examine diverse sociotechnical drivers and barriers and the actor ecosystem involved. We conduct an extensive qualitative case study on nutrient circulation (P and N) in a Finnish context, analyzing over 150 documents and interviewing over 20 diverse actors (from diverse companies through ministries to farmers) involved in nutrient recycling, from biowaste through agricultural biomasses and sludge from municipal wastewater treatment plants. Our study 1) generates an ecosystem actor map uncovering diverse actors enabling nutrient recycling in society; and 2) exposes technological, business, organizational, regulatory, linguistic, visual, and psychological drivers and barriers shaping nutrient circulation. It explains the sociotechnical preconditions for different actor/stakeholder groups to adopt and advocate circular economy (CE) principles for nutrient recycling, which are generalizable to other critical resources. The study contributes to CE research and advises practitioners by providing a comprehensive catalyst toolbox to advance nutrient circulation and facilitate its acceptability and diffusion. [Display omitted] • Qualitative study analyzes drivers/barriers for recycling of critical resources, nutrients. • "Ecosystem" is applied as a metaphor for a multi-actor constellation enabling recycling. • Key actors for nutrient recycling ecosystem vary from farmers and businesses to policymakers. • Catalysts are technical, business, organizational, regulatory, linguistic, visual, and psychological. • A framework is developed for sociotechnical drivers advancing circular economy diffusion. [ABSTRACT FROM AUTHOR]

Anaerobic digestion of food waste within urban areas can generate decentralised renewable energy and support community enterprise activities, thereby contributing to closing the waste-energy-food loop. However, widespread uptake of small-scale, urban anaerobic digestion networks is limited by economic costs and the safe disposal of surplus digestate. This paper uses an interdisciplinary approach to assess the feasibility of anaerobic digestate management through the installation of hydroponics or algae cultivation systems, based on a case study of a micro anaerobic digestion system in London, England. Results show that installing a dewatering sifter together with a hydroponics system is a technically and economically feasible option for digestate enhancement in the urban environment. Its installation is, however, not currently justified for the system under consideration due to cost, regulatory, spatial, and contextual constraints identified using actor-network analysis. Nevertheless, if regulatory and wider contextual issues are accommodated, and more than 30 L of digestate are produced daily, a dewatering and vertical hydroponic system could result in a profit of approximately £100,000 over 10 years. While the microalgal system was also able to upgrade digestate, at present productivity is too low and the capital cost of photobioreactor technology is prohibitively expensive. This underlines the need for technical improvements and low-cost enhancement options to achieve justifiable paybacks until regulatory reforms and the wider economic situation are more favourable to anaerobic digestion treatment within cities. [ABSTRACT FROM AUTHOR]

With the ever-increasing size of anaerobic digesters (AD), the management and disposal of digestate have become a challenging task for AD operators. Anaerobic digestate is rich in nutrients and contaminants; thus, a suitable treatment is required to meet environmental legislation and protect the receiving environment. There has been a thrust among the research efforts in anaerobic digestate management in the last decade. Volarization of digestate into high-value products is necessary to make the AD process more cost-effective. Moreover, digestate utilization helps in recycling the already mined resources. Efforts have been made to use digestate as a feedstock to recover energy and value-added products such as nutrients (N, P), biochar, biofuels, polyhydroxyalkanoates (PHAs), and algal cultivation, which can arguably help to enable the circular economy in modern communities. This communication thoroughly examines the anaerobic digestate-based biorefinery concept and its linkages with the circular bio-economy. This review comprehensively summarized digestate management practices; recovery of renewable fuels and other value-added products from digestate, including bottlenecks and perspectives altogether in digestate management and treatment. The state-of-the-art of commercialization of anaerobic digestate valorization technologies has also been provided. Overall, this review could support decision-makers in identifying environmentally sound and sustainable solutions ahead of time. [Display omitted] • Critically review of the conventional and emerging digestate management practices. • Featured the commercialization of anaerobic digestate valorization technologies. • Key challenge & research needs in development of digestate valorization are explored. • Various pre-treatment methods can be used to improve the quality of nutrients recovered. • Presence of emerging contaminants is a major concern in digestate utilization. [ABSTRACT FROM AUTHOR]

In order to transition from a linear to a circular economy in the organic waste management sector, more of the elements in waste need to be recycled. Use of black soldier fly (Hermetia illucens L.; Diptera: Stratiomyidae) larvae (BSFL) for organic waste treatment has potential to harvest more complex molecules than conventional methods. Many organic waste substrates have high water content (>80%), but the impact on BSFL treatment efficiency of substrate water contents >80% is not known. This study evaluated the impact of high water content food waste on BSFL composting efficiency in terms of waste-to-biomass conversion ratio, material reduction, larval survival and the ventilation required for enabling dry separation of larvae from residue. In total, six water contents ranging from 76% to 97.5% were evaluated in two experimental trials. It was found that increasing water content reduced biomass conversion ratio and survival rate of the larvae, from 33.4% of volatile solids (VS) and 97.2% survival in 76% water to 17.5% of VS and 19.3% survival in 97.5% water. Furthermore, we found that the ventilation requirement for achieving dry separation of larvae from residue could be modelled by estimating the amount of water that would need to be removed, taking into account the water bound in the larvae, and knowing the specifics of the ventilation set-up of the modelled system. The findings could have implications on the waste management sector interested in implementing BSFL treatment, as the findings demonstrate that it is possible to treat wet substrates (such as fruit and vegetable wastes) without any pre-treatment other than grinding and attain an adequately dry residue for enabling dry separation of the larvae from the residue. Unlabelled Image • Impact of water content on fly larvae composting efficiency evaluated • Higher water content reduced process efficiency. • Possible to fly larvae treat substrates with water content 80–90% • Ventilation requirement for attaining dry residue predicted • Enables simple BSFL treatment of wet substrates such as veg & fruit peels [ABSTRACT FROM AUTHOR]

• TSP fertilizer mixed with MB produced an environmentally friendly fertilizer; • The addition of 12% of MB in the TSP had a positive effect on plant growth; • The addition of 30% of MB in the TSP impaired phosphorus diffusion. The cultivation of microalgae in wastewater allows to obtain a biomass concentrated in nutrients and organic material. This biomass added to phosphate fertilizers can promote a slow release of the nutrient and consequently a higher absorption of phosphorus (P). The objective of this study was to investigate P uptake by plants subjected to triple superphosphate (TSP) fertilization, added with microalgae biomass (MB) grown in wastewater. TSP was added with different MB proportions in order to verify if there would be a different behaviour in P release for millet (Pennisetum glaucum L.) plants. With the proportion that maximized P accumulation in plants, a second experiment was carried out to investigate whether MB exerts influence of P diffusion in the soil. Finally, a third trial was conducted in a greenhouse, where TSP and TSP + 12% MB were applied to the soil under different phosphorus doses in corn (Zea mays L.). The proportion of MB in TSP that maximized the increase of P content and concentration in plants was approximately 12% MB. From this proportion, a reduction in the values of the variables analysed in the plant with the increase of the proportion of MB in the biofertilizer was observed. Similar behaviour was observed when evaluating P diffusion in sandy and clay soils. Fertilizers TSP and TSP + 12% MB showed no difference in P diffusion in the soil, while the ratio of 30% MB clearly impaired P diffusion. In a greenhouse, the P content presented significant difference for the tests carried out with TSP and TSP + 12% MB fertilizer, in which the latter provided higher P recovery rate by plants. Therefore, MB added to TSP had a positive influence on plant development and its P recovery capacity when applied in a proportion of 12% MB to the fertilizer mass. [ABSTRACT FROM AUTHOR]