THE PROJECT
«Management and Utilization of Sewage Sludge in the Circular Economy using Green technologies and methods»
This project (acronym: DIALKOP) presents a modern model for the management of biological sludge resulting from municipal wastewater treatment based on the circular economy, testing and using sustainable technologies such as constructed wetlands, methods such as composting and biochar production, and practices such as reuse in agriculture and wastewater treatment, towards the beneficial conversion and utilization of this valuable by-product.
The project is financed by the Green Fund of Greece in the framework of Priority Axis 3: Research and Implementation, of the funding program: “Natural Environment & Innovative Actions 2022”.
In Greece, more than 50% of the sewage sludge produced in wastewater treatment plants (WWTPs) ends up in landfills, with limited reuse (eg in agriculture, composting). With the exception of the two largest cities (Athens, Thessaloniki) where the dried sludge is utilized as a fuel, in the rest small and medium-sized WWTPs of the country (as is the case of Crete) linear management is carried out consisting of thickening and dewatering with mechanical and chemical methods (eg calcification, addition of polyelectrolytes, belt presses, filter presses, centrifuges) and daily transportation and disposal of the dried sludge in landfills.
This strategy is often economically unsustainable due to the high associated costs, as the total sludge management costs could represent up to 40-60% of the operating costs of the entire WWTP due to the high energy consumption and daily transportation.
At the same time, this strategy leads to environmental problems, such as the risk of surface and groundwater pollution, the high consumption of energy and chemicals for the mechanical drying, insufficient drying and stabilization of sludge, and the high environmental footprint due to the energy required and the transportation to a landfill.
Furthermore, landfilling is at the base of the sustainability pyramid as the useful components of sludge are this way not utilized. The adoption of the circular economy principles implies not only the promotion of appropriate practices for the utilization of a useful and nutrient-rich material, but also the adoption of new green treatment technologies which themselves will minimize the environmental footprint of the sludge drying process.
The main goal of the project is to study and present a modern, innovative and integrated model of circular management and utilization of the sewage sludge produced at the wastewater treatment plants, as an holistic environmental solution to the existing management problem based on the circular economy principles.
The aim is to study different technologies and alternative methods in terms of their technical efficiency and suitability to reduce the environmental footprint of sludge management and convert this by-product into a useful material and biosolids. The new materials that will result from the tested processes are also studied for their suitability and improvement they bring in various reuse applications (agriculture, wastewater treatment).
Furthermore, the purpose of the project is to conduct a holistic evaluation of the model and the individual processes and methods, based on a series of studies that take into account environmental, economic and social criteria, in order to determine the benefits arising from the proposed circular management model.
Individual goals of the project are:
- Extended application and study of the green technology of Constructed Wetlands for sludge dewatering in Greece, optimization of the operating parameters for the highest possible efficiency, and comparative evaluation with conventional mechanical dewatering methods,
- significant reduction of the current greenhouse gas emissions in the sector of sludge management due to the use of mechanical dewatering methods, high energy and chemical consumption, and elimination of daily transportation and disposal to landfills,
- study of the utilization of sludge for the production of useful organic materials through co-composting with the plant biomass of reeds from the constructed wetlands and also through the production of biochars,
- comparative quality assessment of the final materials and biosolids resulting from the various processes and application to vegetables for the estimation of production and yield improvement,
- assessment of the economic, technical, environmental and social parameters of all methods and material cycles and studied management scenarios,
- determining the optimal circular management strategy.
The studied circular sludge management model incorporates several points of innovation in its various actions. As a concept and idea, it is a pioneering integrated framework for utilizing a valuable by-product and transforming it into a useful new product with the smallest possible environmental impact. The configuration and the individual combined practices in the management scheme are a model of circular sludge management not only for Greece but also internationally.
WP1 Project Management
WP1 handles the financial and administrative aspects of the project and monitors the progress and fulfillment of objectives and deliverables. WP1 performs day-to-day management and guarantees the correct execution of all tasks and coordination between partners.
WP2 Constructed Wetlands for sludge dewatering
WP2 concerns the research of the green technology of Constructed Wetlands (CW) for sludge dewatering as an alternative technology to mechanical dewatering methods.
CW are a Nature-based solution with their key feature being the use of natural materials (gravel, sand) and plants (reeds) for the treatment. The use of non-recyclable and synthetic materials is avoided, no chemicals are used, there is minimal mechanical equipment, while they can be easily combined with renewable energy sources to cover the very small energy needs.
In Greece there are only a few dozen CW applications for wastewater treatment, and none for sludge dewatering, although the climatic conditions are ideal. CW pilot units are built within the premises of the Wastewater Treatment Plant of Chania owned by the project partner DEYACH. The units function as demonstration system of the technology and for experience gaining in their operation, but also as research units where different construction and operational parameters are studied in order to optimize the design for the country’s climate.
The construction as well as the operation of the pilot units is carried out by the Technical University of Crete (TUC). Regular monitoring of sludge and leachate sampling and physicochemical analyzes is also carried out.
A key advantage that will be demonstrated with the CW technology is the immediate elimination possibility of the daily transport of sludge to the landfill. This comes to satisfy Directive 2008/98 on waste, the provisions of the National Waste Management Plan (Government Gazette 185/A 29.9.2020) and the New Action Plan of Greece for the Circular Economy (Government Gazette 84A/3-5-2022) , according to which the disposal of sludge in landfills should be less than 5% already by 2020 (a target which has not yet been achieved in Greece) and the rest should be used in agriculture or for energy recovery.
WP3 Composting study
Constructed wetlands produce a quantity of reed plant biomass that will be utilized for co-composting with the dried sludge from mechanical dewatering. This process contributes to the circular management in the proposed model, as it avoids the disposal of the plant biomass in the landfill while this material is utilized for the production of a useful product, as required by the relevant national and European legislation.
Composting is included in the list of innovative technologies of the EU circular economy indicators monitoring framework (Y02W, 30/43). Plant biomass facilitates the co-composting of sludge, as it acts as an additional carbon source to achieve the appropriate C/N ratio, while it also acts as a bulking agent to enhance the necessary aerobic conditions in composting and contributes to the biological stabilization of the plant biomass. The produced compost will be used as a soil conditioner, fertilizer, crop ingredient and bio-based product.
Compost, as the biosolids in WP2, are secondary products that can replace mineral-based products such as mineral fertilizers, peat and fossil fuels, the residues of which after use are safely returned to the biosphere, thus closing the carbon and nutrient cycles.
In WP3, three compost rows are created at the facilities of the DEDISA Partner, where there is already a composting unit, consisting of dried sludge and plant biomass as the main substrates, along with small amounts of biochar. The purpose is to investigate the quality of the final compost and to ascertain the optimal conditions. The construction is done by DEDISA, which will also contribute to the operation and monitoring of the piles. Frequent sampling and analysis will be carried out by TUC to determine the main quality parameters.
WP4 Production and characterization of biochar
The biological sludge and plant biomass from the constructed wetlands are also used as raw materials for the production of biochar through pyrolysis.
Biochar is an extremely rich source of carbon with unique properties such as large specific surface area, high porosity, functional groups, high cation exchange capacity and stability. It is suitable for various environmental applications such as adsorbent in wastewater treatment, remediation of agricultural soils, catalyst, construction material and for the reduction of greenhouse gas emissions.
The produced biochar is characterized physicochemically by TUC and used in pilot constructed wetland units for municipal wastewater treatment, in order to evaluate the improvement of the treatment efficiency. The purpose is to present and study yet another innovative application of reusing a material produced from organic waste.
WP5 Reuse in agriculture
The new materials resulting from WP2-4 (dried sludge, biosolids, compost and biochar) will be studied for the improvement they bring in agriculture. This practice is central to the circular economy and is promoted by many national and European provisions and directives.
For this purpose, tomato crop experiments will be conducted in arable soil where the three materials will be used in different proportions. The effect of each material on crop growth and fruit production will thus be assessed.
WP6 Analysis and assessment
According to Eurostat, emissions in municipal wastewater treatment account for approximately 1/5 of the total emissions in the waste sector. Linear sewage sludge management has a large carbon footprint, mainly due to the sludge treatment process itself and then from its transport. The proposed constructed wetland technology can reduce the emissions of the treatment to a very large extent and eliminate the emissions due to transport to a landfill. Composting and biochar production also help mitigate climate change by replacing fossil energy, peat and mineral/chemical fertilizers, sequestering carbon in the soil and avoiding landfill gas emissions.
The circular management of the sludge that will be studied in the project and the utilization alternatives (disposal of dried sludge, composting, biochar production) will be assessed in terms of their life cycle, taking into account all stages from production of the sludge until its final disposal on agricultural land. The most important criteria for ecological assessment are energy and material input and process efficiency. The target parameters of the life cycle analysis are, in particular, greenhouse gas emissions and the consumption of fossil energy sources.
The proposed management model will be evaluated in terms of its financial aspects. There will be an assessment of the construction and installation costs of the individual techniques and technologies within the framework of the circular management model, and a comparative evaluation with the current linear management and the use of conventional technologies (cost-benefit analysis). Multi-criteria analysis will be used for the overall co-evaluation of alternative scenarios and methods. The basic assessment will be based on criteria (economic, technical, legislative, social, characteristics of the final product, environmental) with corresponding weighting factors, where the scores will come from calculations, literature review, and expert opinions.
WP7 Dissemination and communication
This WP will manage and promote the project’s external relations involving all partners to disseminate the concepts, methods, results and main achievements to the widest possible audience and achieve the greatest possible impact.
A dissemination strategy and communication program will be developed that will address the stakeholders, public and private waste management organizations, Municipalities and Regions, related industries and companies, the scientific community and society.
A user-friendly and easily accessible project website will be developed and updated continuously. In addition, project social media accounts will be created for frequent contact with different target groups and dissemination of results.
The communication program also includes information leaflets, short video and publication of the project results in scientific papers and conferences to share the main results of the project with the scientific community and with private and public bodies, open days to visit and present the pilot applications, as well and organization of a symposium involving important stakeholders.
The research of the proposed circular sludge management model and the different technologies and methods are of particular interest for all involved partners (TUC, DEYACH and DEDISA).
TUC as the research body and provider of know-how will utilize the project to implement the model on a larger scale in other regions of the country. It will also promote the results to members of the scientific community, further cementing the institution’s position as a pioneer in the development of ecological technologies.
In addition, the staff of the two public benefit companies-partners will gain new experience in the application of the studied technologies and methods: DEYACH for the operation and performance of the Sludge Treatment Wetlands, and DEDISA for the possibility of co-composting sludge and plant biomass.
For DEYACH, the problems have to do with the technical difficulties and the frequent breakdowns of the mechanical equipment, the high operating costs and the unsustainable nature of the current strategy, as the smaller WWTP choose to transport the sludge to central facilities over long distances. Mechanical dewatering methods provide an incompletely dried non-stabilized product, unsuitable for reuse, which is why it is sent to the Chania Landfill, burdening its operation.
Therefore, the two partners are looking for solutions that will satisfy the institutional framework and have high efficiency, low operating costs and sustainable character. The results and the entire evaluation of the project actions (research part, technical and environmental study, economic-social analysis and implementation) will be used especially by all partners for the replication and implementation of the circular model on a large scale, and their communication to the relevant municipal and regional authorities and environmental business associations.