Recovering our urban bio-waste locally: successful results of the European DECISIVE project
PRESS RELEASE - Biowaste, food waste and other biodegradable natural waste, represents a third of French household waste. This biodegradable waste is a real source of resources that can be used not only to produce energy for electricity and heat, but also to produce high added value products for farmers. While by the end of 2023 all individuals will have to have a practical solution for sorting their biowaste at source*, the multidisciplinary European project DECISIVE has focused on the development of micro-methanisation of biowaste in the urban environment. Coordinated by INRAE, this programme, launched in 2016 with 14 partners** in France, Germany, Spain, Italy, Belgium and Denmark, has made it possible to develop and test an effective local micro-methanisation system, capable of producing both energy locally and a biopesticide that can be used in the fields. From both an environmental and socio-economic point of view, the results of the project, which ends in October 2021, make it possible to envisage the concrete deployment of this circular system.
At a time when demographic, environmental and energy pressure is increasing in urban areas, and at the same time when bio-waste appears to be a resource to be exploited, the management of this waste must be integrated into the sustainable development of territories. The partners in the European DECISIVE project have developed appropriate technologies for the optimal recovery of this bio-waste and tested the full-scale organisation of a micro-methanisation process on a territorial scale.
Proven robust technologies, local energy and a biopesticide output
Several micro-methanisation processes with biogas recovery by Stirling engine[1] have been tested for several years, through two different manufacturers. The consortium, in particular through the INRAE laboratory in Rennes, has also developed a new micro-methanisation process. This new process, which is more energy-efficient, consists of two phases: firstly, the solid biowaste is introduced into a tube system operating like a piston, where it is degraded by the recirculation of a liquid (the leachate). The degradation products extracted by the leachate are then transformed into biogas in a separate tank. At the outlet of the piston, a solid digestate is recovered and can be post-treated for recovery. The DECISIVE project in Spain has tested fermentation on solid substrate to enable the production of a biopesticide.
From a nutrient point of view, the consortium demonstrated that the biowaste, which has a high methanogenic power, can produce a digestate containing mineral nitrogen that can be used as fertiliser. However, the return of the digestate produced to the soil is still a subject of research because, even if biowaste is hygienised[2] before being methanised, the reuse of animal residues from our plates imposes a very strict health framework. The fate of pathogens in biowaste recovery systems therefore remains an important area of research.
An unprecedented life-size demonstration in a dense urban area
After three years of evaluating local biowaste flows and researching the most appropriate technologies for their recovery, a pilot demonstration site was installed in Ecully[3], in the Lyon metropolitan area, in November 2019. The micro-methaniser, built by a Franco-Chinese company, topped by a solar panel, was designed to recover at least 50 tonnes of bio-waste per year to complete the project energetically, i.e. 1 tonne per week. It was designed to produce biogas, 80% of which is used to heat the digester and provide the hot water needed for hygienisation, and 20% of which is used to generate electricity to power the buildings of the urban farm. This pilot plant, unprecedented in a dense urban environment, was planned to be fuelled mainly by catering waste (collective catering, traditional catering and waste from a nearby local produce outlet). Within the urban farm, the objective was initially to recover biowaste collected within a 5km radius, and was designed to produce 20m3 of biogas per day and 1 to 2kWh in cogeneration, and to spread the digestate at the end of the process in the neighbouring fields. Despite the pandemic period, which slowed down collections, the micro-methaniser was able to recover 4.3kg of organic matter per m3 of reactor to produce 15m3 per day of biogas.
Proof of concept of a successful decentralised organisation
On the technological side, the installation of a micro-methaniser in a dense urban area has proved its effectiveness, with the involvement of even neophyte actors. The organisation of a short circuit of recycled organic matter also demonstrates in fine the possibility of creating jobs. This technology, which is easily replicable, has also proved to be adaptable because it can be easily transported according to needs. The Ecully micro-methaniser is now installed in Narbonne, and a new site in Italy capable of treating up to 400 tonnes of waste per year is being installed in a mountainous area.
A German partner is also conducting a study of households to determine whether they are in favour of sorting bio-waste at source. The results of this sociological survey, in households with different socio-economic levels, will help refine the policies to support source separation.
Beyond the technological processes, the success of such decentralised waste recovery management projects will depend on the mobilisation of local players (local authorities, restaurant owners, distributors, farmers, etc.) and the support of the population.
* Energy transition law for green growth of 17 August 2015 **INRAE, coordinator, SUEZ, Refarmers (France); UAB, ENT, Aeris, ARC (Spain); AU (Denmark); TUHH, GEOMAR (Germany), ITS, AT (Italy), ACR+, PSUtec (Belgium)
[1] A Stirling engine is an external combustion cogeneration engine. It is the difference in temperature that modifies the pressure of the gas inside the engine to activate a piston whose mechanical energy turns a coil that produces electricity. The external combustion allows a minimum of purification of the biogas before combustion in the external burner. Conventional cogeneration engines are internal combustion engines. Also in this case the biogas must be cleaned before combustion in order not to damage the engine.
[2] Hygienisation consists of a treatment at 70°C for 1 hour, on waste that has been ground to a maximum of 12mm.
[3] At the Horticultural Training and Promotion Centre (CFPH) in Ecully (69), in collaboration with Refarmers, a local company specialising in urban agriculture.
What is methanisation?
It is a biological process that degrades organic matter in the absence of oxygen. Carried out by micro-organisms, the degradation of organic substrates in a confined and controlled environment maximises the production of a gas, called biogas, which is rich in methane. In the case of injection into the natural gas network, the biogas obtained by this degradation will be purified (the other gases in the gas mixture will be extracted to recover only the methane) in order to obtain biomethane which has characteristics identical to natural gas. At the end of the digester, a paste-like material, called digestate, is obtained. This is a co-product of methanisation in which the fertilising elements (nitrogen, phosphorus, potassium) initially introduced into the methaniser via the substrates are retained. In the same way as livestock manure, this digestate is an organic fertiliser that can be used to fertilise crops.