The National Institute of Applied Sciences of Toulouse (INSA Toulouse) hosted the consortium meeting of the Ecoval Sudoe project in the same French city on Wednesday and Thursday (23 and 24 November, respectively) in order to share and present the progress achieved so far, as well as the next steps to be taken.
The kick-off was at nine o’clock in the morning, where CETAQUA made an introduction and presentation of the project, as well as its contribution to it from a biotechnological perspective to valorise organic waste. Subsequently, the rest of the actors (FEUGA, INSA TBI, NEREUS, USC BioGroup, ADTA, FPNCyL and Porto Ambiente) presented their different contributions to Ecoval Sudoe until midday, when there was a break to resume the activity in the afternoon.
On Thursday, the consortium visited the Ginestous Wastewater Treatment Plant (WWTP) in Toulouse to observe first-hand how the city’s sewage sludge is currently treated. It also analysed its potential for transformation into a biofactory, as pursued by the Ecoval Sudoe model to promote a more sustainable and circular economy.
This consortium meeting is the fifth one held by the project, after the last one organised last June in the city of Porto, hosted by Porto Ambiente. In this type of events, synergies are generated between the different agents and are a key element for the proper functioning of all types of projects, even more so in the case of Ecoval Sudoe due to the multiplicity of actors, interests and challenges faced with the aim of promoting a circular and sustainable business model in a context of green transition.
With more than 17,000 engineers working in all economic sectors, the National Institute of Applied Sciences of Toulouse (INSA Toulouse), a public scientific, cultural and professional institution under the authority of the French Ministry of Higher Education, was created in 1963 and is recognised for the excellence of its training and its students. Its participation in the Sudoe ECOVAL project focuses on three actions: the optimisation of volatile fatty acid production in bioreactors, the evaluation of the methanogenic potential of acidogenesis digestates and the development of a model of the global urban biowaste management system.
Optimisation of volatile fatty acid production in bioreactors
In collaboration with CETAQUA, INSA Toulouse is working to optimise the production of Volatile Fatty Acids (VFA) from biowaste. This production is carried out in a bioreactor that performs acidogenesis. The VFA are then extracted and purified for commercial use. INSA Toulouse uses a dynamic simulation model of the acidogenesis process to describe the evolution of substrates and reaction products according to the operating parameters of the process. This tool makes it possible to choose the operating conditions that lead to the most significant production of VFAs and the most favourable for commercialisation. A collaboration with the company Nereus led to the integration of VFA recovery constraints into the criteria for optimising VFA production.
The progress achieved allows the variability of bio-waste and inhibitions of certain biological processes to be taken into account in order to better predict the quantities and qualities of the products formed.
Assessment of the methanogenic potential of digestates from acidogenesis
After the production of VFA, a material residue remains that can be recovered by methanisation. INSA Toulouse is evaluating methane production on this residue. It is developing an original continuous process that increases methane production and thus bio-waste recovery. This process is based on a coupling between mesophilic digestion of the waste coupled with thermophilic digestion of the digestate. The progress achieved makes it possible to reduce the quantity of sludge to be disposed of thanks to a more thorough degradation of the mixed sludge. We will see this autumn whether these results can be reproduced on acidified sludge waste and then on biowaste.
The development of a model of a global municipal biowaste management system
The global modelling tool allows the assessment of bio-waste management channels at the city level. The objective is to quantify the production of bio-waste in an urban territory and to optimise its collection, transport, treatment, and valorisation into volatile fatty acids and methane. The modelling is developed using data and scenarios from three cities: Toulouse (France), Porto (Portugal) and Palencia (Spain); with different sizes, urban planning, and collection strategies. Toulouse and Palencia are committed to the collection at voluntary drop-off points (VDPs) and composting, while Porto already has a door-to-door collection.
The three case studies are used to compare various treatment solutions: composting and/or anaerobic digestion by 2030 or VFA production. The comparison is made on the basis of flow and energy balances. The cooperation with another partner (Biogroup CRETUS USC) also allows comparison on the basis of the environmental impacts of bio-waste management channels. The model is already developed and simulations of the first scenarios are being carried out.
Ultimately, this modelling tool and the resulting results will help communities and companies to make decisions on the most virtuous management methods from the point of view of environmental impact and economic profitability. It will also allow the identification of priority areas in the sector to be optimised.
One of the objectives of the Ecoval Sudoeproject is to demonstrate the technical feasibility of producing volatile fatty acids (VFA) from urban sludge. To do this, at the Ourense Wastewater Treatment Plant (WWTP), Cetaquahas set up different tests to optimise the generation of acids such as acetic, propionic, or butyric acid from sewage sludge.
In order to determine the most suitable operating conditions for the pilot VFA production plant, different laboratory-scale tests were first carried out, such as batch tests on a 0.5L scale and the operation of semi-continuous reactors of 5L volume, which demonstrated the suitability of sewage sludge as a substrate with high potential for the production of high added value bioproducts with VFA.
The information provided at the laboratory scale has helped Cetaqua technicians to have a first approximation of the VFA production yields that can be obtained from sludge with and without pre-treatment. They were also able to analyse the effect of operating parameters such as pH, feed/microorganism ratio, hydraulic residence time, etc.
On a pilot scale, the technicians have optimised the fermentation process for the production of VFA, obtaining a stream that has to undergo solid-liquid separation, a unitary operation that has had to be perfected thanks to “jar tests” that have made it possible to determine the optimum doses of coagulant and flocculant for the division of the solid and liquid fractions. Thus, the objective of producing a liquid current rich in VFA for the partner NEREUS to study its clarification and concentration and a high-dryness solid cake that INSA will recover energetically has been achieved.
Following these tests, work is now continuing on the pilot plant which, after a start-up phase marked by hydraulic difficulties in operation and the necessary adjustments, is now operating more robustly. It will soon begin to be fed with biowaste.
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The main object of discussion was the work planning for joint tasks of the ECOVAL project and the activities related to the comprehensive urban organic waste management model and measurement of its social and legal impact; and the replicability and transfer of the business model and its environmental and economic assessment.
The city model of Toulouse, where the meeting was held, was also a case of study for the attendees because of its implementation of the bio-waste collection since 2019. Chloé Maisanno, head of the “Observatoire Régional des Déchets et de l’Economie Circulaire en Occitanie – ORDECO” (Regional Observatory of Waste and Circular Economy in Occitania) showed her interest in the development of the project and participated at the last session on Friday morning.
The participants concluded that the meetings were a success in achieving their objectives and took the opportunity to exchange results and approaches taken in each of the laboratories. A follow-up reunion will take place in October.
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