But the valorisation rate is still very low (around 25%), and most common valorisation processes currently used generate low value products.
Therefore, many initiatives have been started to find solutions. Some of them are based on the improvement of the collection systems. The quality of the collected biowaste is key to its subsequent valorisation (better quality permits better applications). Other efforts are focused on the development of new processes able to get a higher value from biowaste.
SCALIBUR project
SCALIBUR is a Horizon 2020 project composed of 20 partners and coordinated by the research centre ITENE, aiming to develop new technologies for improving biowaste management. It started in November 2018 and finished in October 2022. Therefore, final results are available. They will be explained in this article.
The work in the project has been centred on three biowaste fractions. First, the Organic Fraction of Municipal Solid Waste (OFMSW), which is the material collected in the container for the selective collection of biowastes generated at home. Second, there is HORECA biowaste, which is the organic residue generated in hotels, restaurants, and cafés. Third, the sewage sludge, which is the bioresidue obtained after the treatment of waste water.
SCALIBUR had two main objectives: (1) to improve biowaste collection and management, (2) and to create high value products from biowaste. The improvement of biowaste collection and management in the project has been based on the introduction of innovative technologies to measure the quality of the organic matter, the optimization of collection routes and the implementation of innovative biowaste monitoring systems. The creation of high value products is based on the development of new biological and chemical processes able to degrade the residue for obtaining new raw materials.
Improvement of biowaste collection and management
Firstly, an innovative system of sensors was developed and tested in collection containers. This system not only measures the fill level, but also the degradation level of the organic matter. The measurement is done in real time. This allows to automatically know if the container needs to be collected urgently or if collection can be postponed. This information is useful to optimize collection routes, therefore saving time and fuel during collection. Moreover, it allows for the best quality in the organic matter collection, which is key to ensuring the necessary conditions in subsequent valorisation processes.
The information provided by the sensors, the decisions on collection (or not), and the connection with collection maps are all controlled by an IT platform that was also developed and tested in the project through real pilots.
Moreover, SCALIBUR worked on the development of innovative pre-treatment processes to prepare the organic materials for the subsequent treatments. Processes studied for the subsequent hydrolysis of OFMSW were monitoring, manual separation, trituration, trommel separation, electromagnetic separation, homogenization, stabilization, and drying.
As an example, a new system for the characterization of the quality of the OFMSW in the treatment plant was developed. This system permits the visualization and calculation of percentages of organic matter and rejected material. This allows for clear information to be used to decide in real time on the most adequate subsequent pre-treatment processes.
Furthermore, a deep study of the main problems occurring in the cities was carried out together with stakeholders. These problems were classified in several categories, which are: social awareness, collection, transport, sorting, pre-treatment, and characterization (see Table 1). Then, a list of best practices on each of these topics was developed together with partners, cities, and other companies and stakeholders.
In addition, a sheet was prepared for each best practice, including the description, instructions for implementation, an example, and the expected benefits (environmental, economic, and social). It should be noted that the contribution of the City of Lund (a partner in the project as an “example” city) was crucial for the development of these best practices.
All these innovations were tested in three pilot cities (Madrid, Spain; Albano-Laziale, Italy; and Kozani, Greece). The technologies tested in each pilot were slightly different. Madrid tested actions on social awareness, sorting, pre-treatment, and characterization, while Albano and Kozani implemented technologies on collection, transport, and characterization.
Results show important improvements in each city. In Madrid, the awareness and education campaigns led to an increase in the organic matter content from 2019 to 2022, from almost 75 percent to nearly 83 percent. In Kozani, due to the optimization of the routes, there was a 64% reduction in the distance travelled to collect 1 tonne of organic waste.
Finally, Albano Laziale reduced the total quantities of waste collected (-6.83%) while also increasing the quantity (and share) of organic fraction collected, from 25.59% to 29.49%. Regarding route optimization, Albano Laziale reduced by 15.15% the distance travelled during collection and therefore fuel consumption.
High value products from biowaste
Municipal solid waste is known to have a huge environmental impact in terms of greenhouse gas emissions, mainly because of the amount of waste that ends up being landfilled or incinerated. In the SCALIBUR project, biowaste valorization processes were developed to help implement the circular economy in the European Union by giving value to the organic fraction of municipal solid waste (OFMWS), HORECA waste, and sewage sludge from the water treatment plants. During the project, new sustainable products from the defined biowaste streams were developed.
HORECA and the organic fraction of municipal solid waste
The objective of the recovery of HORECA and municipal waste in the project was to develop new products from these residue flows, which are destined for landfill. For this, different processes were developed, such as the enzymatic hydrolysis of waste and insect rearing on the residues.
The valorisation of the organic fraction of the municipal solid waste (OFMSW) to extract the sugar fraction contained with the aim to manufacture different bio-based products (biopesticides and bio-based polyesters) starts with an enzymatic hydrolysis of the biowaste, where an enzymatic cocktail specifically designed to address the hydrolysis of the carbohydrate components in the OFMSW (cellulose and starch) was used. Then, an enzymatic hydrolysis process has been upscaled and validated using a high solid load for the production of a sugar enriched concentrated syrup. After this process, two products were produced; the solid fraction was used for the production of biopesticides, and the liquid fraction, enriched in sugars, was used for the synthesis of bio-based polyesters and biopesticides.
The concentrated sugar fraction obtained from the OFMSW’s conversion processes has been aimed at producing bio-based and biodegradable polyesters for both food packaging and collection bag waste. The production of these new products helps reduce the amount of virgin material while boosting the use of compostable end-of-life products. The use of compostable packaging will contribute to the success of good practices in OFMSW collection and management and its further valorization into highly valuable compost. Moreover, a territorial cluster of circular initiatives will accelerate the transition to a greener, more resilient economy, able to provide sustainable responses to the needs of the involved areas.
Furthermore, insects like black soldier flies (BSF, Hermetia illucens) can convert in a very efficient way kitchen and restaurant scraps, or simply organic materials, into biomass rich in proteins, lipids, and chitin.
Chitin and its derivatives represent a well-reviewed biopolymer with many beneficial applications. The preparations for chitin and its derivatives as a biomaterial vary according to process conditions and potential applications. However, their main sources are crustaceans, and research on alternative sources is still under development.
In the SCALIBUR project, chitin was optimally extracted from adult BSF through demineralization, deproteinization, and decolorization processes. The extracted chitin fraction was fully characterized, and then it was used to prepare nanofibres (Ch-NF) through a mechanical treatment. Therefore, the SCALIBUR project demonstrated the potential of black soldier fly insects to obtain chitin by chemical methods for the further development of nanofibres with potential interest in food, biomedical, or cosmetic applications.
Sewage sludge
In the case of sewage sludge, the objective was to develop processes to produce new products with high added value, such as biopolymers, biogas, and biopesticides.
Within the framework of the SCALIBUR project, a technological solution was designed and developed to increase efficiency in the anaerobic digestion process of sludge in a water treatment plant (WWTP), carried out in two stages.
On one hand, the dual digestion consists of a first reactor operated under thermophilic conditions where hydrolysis of the sludge to be treated occurs, producing hydrogen as a by-product. During this process, the concentration of volatile fatty acids (VFA) that have a high biodegradability is increased. Feeding hydrolyzed sludge to the second reactor operated under mesophilic conditions favours a drastic increase in biogas production compared to conventional digesters (increase of 38%).
During the anaerobic digestion process, a biogas stream rich in methane and carbon dioxide is produced. In SCALIBUR, a bioelectrochemical reactor was designed with the aim of reusing this current of carbon dioxide to transform it into products with high added value (acetic acid). During the piloting of the bioelectrochemical reactor (in the Czech Republic and Spain), acetic acid productions of 1.5 g/L have been achieved, demonstrating the capacity of new electrochemical technologies to reduce carbon dioxide emissions into the atmosphere while transforming them into valuable products.
On the other hand, municipal wastewater sludge is microbiologically active and is rich in bacteria that can store biopolymers, namely polyhydroxyalkanoates (PHAs). Furthermore, fermentation of the organic fraction of municipal solid waste (OFMSW), and/or wastewater sludges can yield VFAs as a substrate for bacteria to accumulate these valued biopolymers. The SCALIBUR project developed methods for demonstrating and upscaling PHA production and recovery using waste activated sludge and VFAs. PHA is a biodegradable polyester with thermoplastic properties similar to those of fossil fuel-based polymers. The PHA was produced in infrastructure at pilot scale, including the process steps of PHA accumulation, PHA-rich biomass dewatering, green solvent extraction, and post-treatment towards bioplastics with food contact quality.
PHA was produced for end-users to be able to evaluate their interest. PHA production methods were optimized to enable the production of a food packaging prototype, and the thermal properties obtained are similar to those of commercial PHBV. To obtain results on the processability of the developed material, pots were manufactured (see photo). The SCALIBUR PHBVs were used as a property modifier. They enabled the enhancement of critical mechanical properties (toughness) compared to the commercial PHB.
The SCALIBUR multi-stakeholder engagement approach
In addition to the technical dimension for improving biowaste management, the SCALIBUR project has also implemented a variety of multi-stakeholder engagement activities in three pilot cities, Madrid (Spain), Albano (Italy), and Kozani (Greece). Consortium partners implemented a tailored approach based on a quadruple-helix engagement model that included stakeholders from the realms of academia, industry, policy, and civil society.
At the core of this approach lies the Biowaste Clubs concept, a stakeholder-driven process building on a long-term, inclusive dialogue with all actors aiming to develop local leadership and trigger innovative strategies and policies. Throughout the project, the Biowaste Club’s ad-hoc meetings and activities (i.e., events, workshops, and trainings) have provided a neutral stage for key stakeholders to meet and discuss, and thus to keep track of stakeholders’ motivations, drivers, challenges, and needs, all of which contribute to the development of shared (bio)waste management and valorisation visions and roadmaps at the local, regional, national, and EU levels.
Furthermore, the SCALIBUR project aimed to foster social innovation through a better understanding of citizens’ knowledge and perceptions of (bio)waste as a resource. Interactive do-it-yourself workshops, surveys, campaigns, and exhibitions have been organized revolving around the concepts of the bio- and circular economies at the city and regional level. The aim was not only to increase knowledge around emerging technological solutions for the generation of bio-waste-based products, but also to enhance citizen and consumer acceptance of those specific types of products. In the short term, these activities have enabled the kick-off of innovative collaborations across cities, regions, and countries, leading to societal innovation in the long term.
The Biowaste Hub
To facilitate the connection between biowaste stakeholders, SCALIBUR also developed an interactive platform called The Biowaste Hub.This platform aims at connecting waste and wastewater management companies, business and local service providers, government municipalities, industry associations, academia, and the scientific community with end-users of bio-based and biodegradable polymers, developers of bioproducts, and generators of urban biowaste (retailers, hotels, restaurants, and individuals or professionals with interest in biowaste).
Moreover, the platform permits the transfer of all technologies developed within the project. Concretely, it lets users discover innovative processes and check for best practices. The objective of the platform is to grow even after the project in order to be the reference network on biowaste.
Environmental, technoeconomic, and social improvement
SCALIBUR also studied the sustainability of all technologies developed. This work was done in parallel with the technological development in order to identify potential aspects to be improved during development and testing. The study considered the three pillars of sustainability: environment, economy, and society. All these studies were done with a life cycle approach to consider all aspects affecting the whole value chain.
The environmental study showed that with the implementation of the value chains developed in SCALIBUR, some improvements in the environmental impact were achieved when compared to conventional treatments or conventional products:
- Biochemical conversion of the organic fraction of MSW (municipal solid waste) into biodegradable polyesters and biopesticides: In this value chain, when comparing the results of the climate change category for the conventional pesticide to the fermented solid pesticide developed in SCALIBUR, it can be concluded that the impact is reduced by about 28.5%.
- Insects to valorize organic waste from ROW (residue organic waste). The aim of this value chain is to obtain proteins. Therefore, the valorisation of ROW by insect rearing in order to obtain proteins that has been developed in SCALIBUR, was compared with a different type of production of proteins, such as those whose origin source are microalgae. The results indicated that the impact in the climate change category is reduced by around 60%.
- Bioconversion of sewage sludge and OFMSW through biochemical and bioelectrochemical routes: In this value chain, two routes can be followed, one that aims to obtain VFA and another that produces PHVB. In both cases, when comparing the results of these routes with the conventional treatment, the environmental impacts get reduced, especially in the climate change category. In this category, the impacts decrease by 98% for the VFA production and 49% for the PHBV production.
In relation to the social-LCA (life cycle assessment) that was also carried out, it was proven that there is potential for creating new job opportunities through the establishment of these new value chains. The study showed that in 65% of the companies involved in SCALIBUR, new jobs were created. Also, great results were obtained in the social acceptability of the bioproducts, demonstrating higher levels of acceptability among citizens, workers, and value chain actors.
Conclusions
The SCALIBUR project worked for four years on the development of new technologies able to improve the collection as well as obtain high value products such as bioplastic films, biopesticides, biomaterials, and food and feed products.
The introduction of these technologies in the market is an opportunity not only for a better treatment of biowaste but also for the development of new value chains and industrial opportunities, especially taking into account the amount of biowaste generated, which can be considered raw materials for these processes. Therefore, SCALIBUR represents a step forward on the road to a circular economy.
