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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]

[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]

Promotion of the circular economy (CE) has become one of the key policy objectives in the EU in the late 2010s. The power of the concept lies in the promise of decoupling economic growth from the increasing usage of virgin resources by closing the material loops. In this article, we investigate the material politics of the CE by means of an in-depth case study of how one pioneering biogas company in Finland struggled to undo a disruptive regional manure surplus by turning it into a resource in energy and fertilizer production. We treat this novel nutrient recycling business model as a political technology that aimed to rearrange existing metabolic relations in order to solve the problem of intensive pig farming that generated too much manure for sustainable utilization in the area. At the same time, their business model clashed with the various categorizations and technologies of governance that stabilized the status quo. These clashes embody the underlying societal tensions of the CE transition, which do not manifest themselves as open conflicts in public arenas. We claim that these obstacles point to challenges of unmaking material surplus with CE business models when the surrounding economy leans on a linear material flows and keeps growth on track. [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]

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]

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]

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]

• Inorganic fertilizers account for 42 % of N and 90 % of P inputs to Ontario's food systems. • Ontario loses 298 kt-N/y (58 %) and 15 kt-P/y (29 %) of annual inflow to the environment. • Cropland erosion contributes 103 kt-N/y (35 %) and 14 kt-P/y (90 %) of total N and P losses. • A 30 % simulated increase in diversion rates reduced reliance on inorganic fertilizer by 28 kt-N/y and 9 kt-P/y. • Food waste, manure and biosolids management require technological and policy interventions. Resource scarcity, energy requirements, and environmental pollution resulting from the production and use of nitrogen (N) and phosphorus (P) fertilizer have spurred an interest in a circular approach to nutrient management. An analysis of N and P flows in Ontario's food systems was carried out to quantify relevant flows and stocks, evaluate alternative management scenarios and identify points of loss to the environment. The results showed that mineral fertilizers accounted for 42 % of N and 90 % of P inputs to Ontario's food systems. Of the total amount of food produced, 153 kt-N/y ± 27 % and 28 kt-P/y ± 21 % in grain and oilseed were fed to animals. About 58 % (298 kt-N/y) and 29 % (15 kt-P/y) of the annual supply of N and P were lost to the environment. Major nutrient losses were from the crop production system, through erosion, contributing 35 % (103 kt-N/y ± 10 %) and 90 % (14 kt-P/y ± 51 %) of the total N and P lost. Over half of the N and P in the waste subsystem was disposed of in landfills or incinerators, where further N losses occurred through leaching and volatilization. Ontario's reliance on inorganic fertilizer supply could reduce by 28 kt-N/y and 9 kt-P/y if the current waste diversion rates were to increase by 30 %. No single waste management scenario could effectively circularize N and P flows in Ontario's food system. However, investment in new technologies might help to recover nutrients from manure and wastewater treatment systems efficiently. [ABSTRACT FROM AUTHOR]