The food provisioning of European cities depends on the global food supply system. However, both economic crises, environmental pressure and climate change effects represent a risk for food chain stability. Urban agriculture (UA) increases the self-sufficiency and resiliency of cities and is able to deliver positive environmental and social benefits. However, its efficacy depends on several variables, including the type of UA and the geographical location of the city. This paper analyses ReFarmers’ pilot farm, a vertical high-yield hydroponic croft located in the urban area of Lyon, France, from a life cycle perspective. The results show that the hydroponic farm performs better than cultivations in heated greenhouses, and similarly to conventional open field farms. Moreover, the source of the electricity input is a determinant factor that, if carbon neutral (e.g. wind energy) allows vertical hydroponic production to outperform the two conventional types of agriculture. Read the paper here.

Solid-state fermentation (SSF) is a promising technology for producing bioproducts from organic wastes. The objective of this study is to assess the feasibility of using digestate as substrate to produce hydrolytic enzymes, mainly cellulase and xylanase, by exploring three different inoculation strategies: (i) SSF with autochthonous microbiota; (ii) non-sterile SSF inoculated with Trichoderma reesei and (iii) sequential batch operation to select a specialized inoculum, testing two different residence times. Native microbial population did not show a significant cellulase production, suggesting the need for a specialized inoculum. The inoculation of Trichoderma reesei did not improve the enzymatic activity. On the other hand, inconsistent operation was achieved during sequential batch reactor in terms of specific oxygen uptake rate, temperature and enzymatic activity profile. Low cellulase and xylanase activities were attained and the main hypotheses are non-appropriate biomass selection and some degree of hydrolysis by non-targeted proteases produced during fermentation. Read the paper here.

The circular economy concept offers a number of solutions to increasing amounts of biowaste and resource scarcity by valorising biowaste. However, it is necessary to consistently address the environmental benefits and impacts of circular biowaste management systems (CBWMS). Various decision support tools (DST) for environmental assessment of waste management systems (WMS) exist. This study provides a review of life cycle assessment based WMS-DSTs. Twenty-five WMS-DSTs were identified and analysed through a shortlisting procedure. Eight tools were shortlisted for the assessment of their applicability to deliver sustainability assessment of CBWMS. It was found that six tools model key properties that are necessary for assessing the environmental sustainability of CBWMSs, including waste-specific modelling of gaseous emissions, biogas generation or bioproduct composition. However, only two tools consider both waste-specific heavy metals content in bioproducts and the associated implications when applied on soil. Most of the shortlisted tools are flexible to simulate new technologies involved in CBWMS. Nevertheless, only two tools allow importing directly new background data, which is important when modelling substitution of new bioproducts developed in emerging biowaste refineries. Read the full paper here.

This study presents a comparative analysis of the environmental and economic performances of four integrated waste and wastewater management scenarios in the city of Aarhus in Denmark. The purpose of this analysis is to deliver decision support regarding whether (i) the installation of food waste disposers in private homes (AS1) or (ii) separate collection and transport of organic waste to biogas plants is a more viable environmental and economic solution (AS2). Higher environmental benefits, e.g., mitigation of human health impacts and climate change, are obtained by transforming the existing waste combustion system into scenario (ii). Trade-offs in terms of increased marine eutrophication and terrestrial ecotoxicity result from moving up the waste hierarchy; i.e., from waste incineration to biogas production at wastewater treatment plants with anaerobic sludge digestion. Scenario (i) performs with lower energy efficiency compared to scenario (ii). Furthermore, when considering the uncertainty in the extra damage cost to the sewer system that may be associated to the installation of food waste disposers, scenario (ii) is the most flexible, robust, and less risky economic solution. From an economic, environmental, and resource efficiency point of view, separate collection and transport of biowaste to biogas plants is the most sustainable solution. Read the paper here.

The main goal of this work is the production of a biopesticide through solid-state fermentation of biowaste digestate inoculated with Bacillus thuringiensis (Bt) at pilot scale using different configurations of reactors. Fermentations were carried out using insulated and non-insulated, stirred and non-stirred reactors at different scales (10, 22 and 100 L) in order to assess the influence of the reactor configuration on the biopesticide production process. A maximum temperature of 60 °C was reached in 10-L insulated non-stirred reactors where increments of Bt viable cells and spores with respect to initial values of 1.9 and 171.6 respectively, were attained. In contrast, when temperature was regulated by using 22-L non-insulated stirred reactors the increment of viable cells and spores were 0.8 and 1.9, respectively, at a stable temperature of 27 °C. When the non-insulated stirred reactor was scaled up to 100-L, the increase of viable cells and spore counts were 1.2 and 3.8 respectively, with an average temperature of 28 °C. These results demonstrated that the election of a proper reactor configuration is important when considering the development of a new SSF process, especially when dealing with non-conventional substrates as digestate. Read this paper here.

Food waste (FW) storage influences its physical–chemical characteristics and anaerobic digestion (AD) performance. In this work we present the results of two weeks long experiment where two types of FW were stored in dedicated cells (10 L and 300 L). Air was evenly flushed on the top surface of the substrates and then analyzed to identify and quantify possible gaseous emissions. Solid and liquid fractions were also periodically sampled and analyzed for total solid, volatile solid, ammonia and VFA contents. Results showed that storage initiated a hydrolysis process that modified the physical structure of FW, leading to the production of gases (CH₄, CO₂ and ethanol) and a partly liquefied FW. Depending on experimental conditions, a fraction between 61 and 70% of the initial substrate remained solid at the end of the storage period. In the liquid phase, a large proportion of lactic acid was measured with maximum contents of 5.9 and 14.8 g/kg_vs for the small-scale experiments with two different FW types and 3.0 g/kg_vs for the large-scale experiment, leading to inhibition of the biomethane potential (BMP) tests. In conclusion, this work showed that when storage of FW is needed before AD, the optimal time recommended to keep a high methane yield is one week. Read the paper here.

Digestate from biowaste was assessed as a potential source of bioproducts of commercial and industrial interest through solid-state fermentation. The targeted bioproducts were hydrolytic enzymes (cellulases and proteases from autochthonous microbiome), biosurfactants (sophorolipids produced from Starmella bombicola) and biopesticides (produced from Bacillus thuringiensis). Low cellulase production was observed within the range of 0.5–1.5 FPU g⁻¹ DM while protease production showed two discrete peaks of 66 ± 8 and 65 ± 3 U g⁻¹ DM at 3.5 and 48 h, respectively. Low sophorolipids production was also obtained, with a maximum yield of 0.02 g g⁻¹ DM using hygienised digestate supplemented with external sugar and fat sources. Biopesticides produced by B. thuringiensis were successfully at 72 h of operation, reaching a maximum spore production of 8.15 ± 0.04 (10⁷) CFU g⁻¹ DM and 2.85 ± 0.22 (10⁷) CFU g⁻¹ DM using sterile and hygienised digestate, respectively. These biopesticides could contribute to the substitution of chemically produced pesticides, moving towards a sustainable digestate management in a circular economy scheme. Read the paper here.

Innovative small scale treatments solutions are currently proposed to handle the growing need of biowaste valorization through a more circular economy. These new approaches are designed to be embedded in a decentralized treatment scheme which raises new challenges for the biowaste management at the territorial scale. This study, aimed at developing a method to design decentralized and micro-scale Anaerobic Digestion (mAD) networks in urban and peri-urban areas. A mixed integer linear program (MILP) was set up to identify the number of mAD, their sites and their capacities in order to minimize the payload-distances of biowaste and digestate transportation while taking into account the technical constraints of the system. A Geographic Information System (GIS) methodology was developed to feed the MILP model with very fine-scale data about (1) the location and the characterization of the biowaste sources and of the digestate outlets (agricultural areas), and (2) the location of the potential sites for mAD based on a multi-criteria analysis that includes environmental regulations, urban planning rules, site accessibility and heat outlets for valorization. The method was applied to the territory of The Grand Lyon Metropole (534 km²) in France. Optimized mAD networks were identified through the MILP according to different scenarios tested. Read the paper here.

A method aiming at improving source-separation performance of household food waste (FW) was investigated in two areas with different socio-economic characteristics in Lübeck, Germany. This included the
test of a new FW collection system including the distribution of small collection buckets to each household. In addition, an information event was organized and households were provided with information material including a waste sorting guide. The study also aimed at assessing the FW avoidance potential. A method for waste composition analysis for FW from households was applied for the assessment. Both areas showed an increase of the source-separation of FW from 17.4% to 60.3% (A, socio-economic low area) and from 16.6% to 65.7% (B, socio-economic medium area) respectively. Compared to the waste composition in the bio-waste (BW) bin prior the investigation, macroimpurities (including paper waste) reduced from around 6.1% to 0.6% (A) and from 13.6% to 1.2% (B). In this respect, the investigated collection system showed a significant improvement to the regular waste collection system. Read the paper here.

A novel aeration strategy has been developed at lab and bench-scale for Bacillus thuringiensis (Bt) derived biopesticides production through solid-state fermentation, using a mixture of digestate and biowaste as substrates. A Box-Behnken design was performed to select key parameters of the spore production process, being temperature and biodegradability the factors with a significant effect. Further tests confirmed the importance of oxygen content for spore production. Thus, a two-stage aeration strategy consisting of a microaeration phase followed by a high-rate aeration period was developed and tested. The production strategy was validated in a 22-L reactor using two different strains (Bt kusrtaki, Btk, and israelensis, Bti), demonstrating the robustness of the protocol. Maximum production of 1.3 × 10⁸ spores g^-1 dry matter for Btk and 4 × 10⁸ spores g^-1 dry matter for Bti were obtained, representing a final yield of 5 and 29 spores produced per initial CFU, respectively. Read the paper here.

This study presents a comparative analysis of the environmental and economic performances of four integrated waste and wastewater management scenarios in the city of Aarhus in Denmark. The purpose of this analysis is to deliver decision support regarding whether (i) the installation of food waste disposers in private homes (AS1) or (ii) separate collection and transport of organic waste to biogas plants is a more viable environmental and economic solution (AS2). Higher environmental benefits, e.g., mitigation of human health impacts and climate change, are obtained by transforming the existing waste combustion system into scenario (ii). Trade-offs in terms of increased marine eutrophication and terrestrial ecotoxicity result from moving up the waste hierarchy; i.e., from waste incineration to biogas production at wastewater treatment plants with anaerobic sludge digestion. Scenario (i) performs with lower energy efficiency compared to scenario (ii). Furthermore, when considering the uncertainty in the extra damage cost to the sewer system that may be associated to the installation of food waste disposers, scenario (ii) is the most flexible, robust, and less risky economic solution. From an economic, environmental, and resource efficiency point of view, separate collection and transport of biowaste to biogas plants is the most sustainable solution. Read the paper here

The biowaste refinery concept has received significant attention in recent years as a sustainable alternative the petroleum refinery, exploiting the biowaste for producing high value bioproducts. However, waste-based biorefineries mainly apply homogeneous waste streams from agriculture and food processing as feedstock. This paper presents the state of the art of mixed-biowaste biorefinery concepts. We identified 20 studies that use the organic fraction of municipal solid waste (OFMSW) as feedstock, producing enzymes, bioplastics, biopesticides and other high value products. Valorisation efficiency (output product per kg OFMSW) and potential revenue by valorising the OFMSW into different products (Euro/ton OFMSW) was analysed for the identified studies. It was found that enzymes have the highest potential revenue followed by biopesticides and bioplastics. Developing biorefineries applying OFMSW as feedstock presents a promising opportunity for moving up the waste hierarch through coupling the waste and production sector in a future circular bioeconomy. Read the paper here

Processing of food is linked to unavoidable and inedible food waste that, despite efforts to minimize waste, will persevere. It nevertheless represents a stable feedstock for the future bioeconomy value chains and products. This study presents a systematic review of 149 examples from the scientific literature using inedible, unavoidable food residues and wastes for the production of value-added bio-based compounds that could substitute synthetic chemicals production. The main high-value products investigated are organic acids, bioplastics, col-orants, enzymes and other platform chemicals. We found 44 examples of acid production with high variability in output (from 43 to 640 g kg −1 waste), 9 examples of bioplastics (from 0.28 to 49 g L −1), 26 examples related to colorants (from 0.04 to more than 400 mg per 100 g), 22 cases of enzyme production (from 6000 Ug −1), 4 examples of protein (23.6 to 38.5 %wt. DM) and 44 cases of other high-value molecules such as pectin and single cell oils. Our findings highlight fermentation as a key technology for the valorization of the studied feedstock, with 76 examples out of the 149 reviewed. The review process also uncovered important limitations related to the lack of standardized food waste definitions, a barrier that is discussed and for which solutions are proposed. At the light of our findings, we further proposed guiding criteria towards the sustainable development of future biorefineries based on food waste. This work touches upon several Sustainable Development Goals, in particular goals 8.2, 9.5, and 12.3. Read the paper here

tural causes (pests), v) inedible due to ineffective management and vi) not accounted for. Category I encompasses surplus food only; category II-V food waste and category VI food losses. Based on this, an updated pyramid for food waste hierarchy is proposed, distinguishing surplus food and a new category for material recycling, in order to reflect the future food waste biorefineries in the circular bioeconomy. Nutrient and energy recovery are two separate categories and the terms recovery and recycling are clarified. Finally, a circular economy framework is presented for food surplus and waste, considering closing the loop throughout the whole food supply chain, in connection with the concept of strong and weak sustainability. This is presented along with a review of key EU policies related to food waste and examples of initiatives from the Member States. Read the paper here.

Bioaccumulation of cadmium (Cd) in the agricultural soil constitutes a dangerous risk for the health of both the environment and humans. Especially in the European Union, a large amount of Cd in agricultural topsoil originates from mineral fertilizer application. In this context, the EU has recently adopted the Regulation (EU) 2019/1009 with the aim to establish stricter limits for Cd presence in fertilizer products and to promote a higher use of fertilizers from organic sources. This paper discusses the future implications of the new regulation to limit the presence of cadmium (Cd) in agricultural soils and food products. The Regulation (EU) 2019/1009 represents an important step of the EU circular economy action plan with its aim to encourage the production of low cadmium content fertilizers. This paper focuses on the limits of the Regulation (EU) 2019/1009 and on the need for complementary policy instruments to protect and conserve agricultural soil health. We highlight the recently proposed, and subsequently withdrawn, EU Soil Framework Directive (SFD) as a meaningful complementary policy tool in the context of a renewed effort to pursue protection and conservation of soil health. Read the paper here.

What are the effects, measured as flows of biogenic carbon, plant nutrients, and pollutants, of moving organic waste up the waste hierarchy? We present a case study of Denmark, where most of the organic fraction of household waste (OFHW) is incinerated, with ongoing efforts to increase bio-waste recycling. In this study, one-third of the OFHW produced in North Zealand, Denmark, is diverted away from incineration, according to the Danish Waste Resource Plan 2013–2018. Co-digestion of OFHW, and digestate application on agricultural soil, utilizes biogenic carbon, first for energy conversion, and the remainder for long-term soil sequestration, with additional benefits for plant nutrient composition by increasing the N:P ratio in the digestate. We show a dynamic model of the biogenic carbon flows in a mix of OFHW co-digested with livestock manure and sewage sludge, addressing the contribution of OFHW to long-term carbon sequestration compared to other agricultural residues and bio-wastes over a time span of 100 years. In addition, we trace the associated annual nutrient and cadmium loads to the topsoil. At constant annual input rates and management practices, a diversion of 33% of OFHW would result in an increased organic carbon build-up of approximately 4% over the current amounts applied. The addition of OFHW, moreover, beneficially adjusts the N:P ratio of the digestate mix upwards, albeit without reaching an ideally high ratio by that measure alone. Cd loads from OFHW remain well below regulatory limits. Read the paper here.

This paper reviews the literature relating to a type of local bio-based circular economy (BCE) where food waste (FW) is effectively recycled to advanced bio-refineries to produce multiple ecosystem services (ES) including energy, biofertilizer and other value-added products and services. The biofertilizer is applied within urban and peri-urban farms to close the bioresource loop. Such BCE concept has been proposed in several EU countries with varying degree of success in long-term operations. We systematically review the ES of BCE and identify the ES, which are not properly compensated by the market. On this basis, we further review the potential regulatory and supporting mechanisms, which could incentivize the successful implementation of BCE and overcome the market/policy failures. We find that single regulatory instrument at the government and authority level could be compromised by poor governance and practices at other levels, and therefore may not reach its full potential. Instead, we propose a multi-level regulatory and supporting system, which combines the strengths of top-down and bottom-up governances and motivates the self-governance of industry and citizens. We conclude by highlighting a need for multi-level governance research supporting urban sustainable transitions, with a focus on constructing ‘policy portfolios’ from a systems perspective to better engage government, firms, citizens and other stakeholders. Read the paper here.