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This page contains the scientific papers published throughout the DECISIVE project’s lifetime which reflect the work DECISIVE’s scientific project partners were doing in order to achieve the objectives of the project. The scientific papers also report on different stages of the project and the development of the technologies necessary for the innovative decentralised biowaste management scheme, such as DECISIVE itself.

The scientific papers are listed below chronologically, the expanded menu gives the abstract while the full paper is available through the link, included in each abstract.

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.

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/kgvs for the small-scale experiments with two different FW types and 3.0 g/kgvs 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.

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