The biogas production process at La Chapelle-Neuve
Anaerobic digestion is a key step in the energy transition towards a more sustainable future: it turns agricultural organic waste into renewable energy. The technology brings many environmental benefits, such as a reduction in greenhouse gas emissions and the production of natural fertilisers, as well as social and economic ones, such as local job creation and a circular economy, while supplying the area with dispatchable energy.
In practice, the project will produce biogas from 52.7 tonnes/day of exclusively agricultural organic waste, in a collective, human-scale anaerobic digestion unit. It will produce 11 GWh/year of biogas injected into the distribution network at 116 Nm3/h*, enough to heat the equivalent of 2,500 new homes (each using 4,400 kWh/year), while turning the digestion residues into natural fertilisers. This will reduce dependence on chemical (fossil-based) fertilisers and support more sustainable farming.
By favouring short economic and energy supply chains, the project makes efficient use of local resources while contributing to a sustainable energy transition. Converting organic waste into biogas and natural fertilisers will reduce dependence on fossil fuels, create local jobs and cut greenhouse gas emissions.
* Nm3 stands for “normal cubic metre”, a unit measuring the volume of a gas at 0 °C and 1 atmosphere.
Diagram of the anaerobic digestion project: 100% agricultural
The project is exclusively agricultural because one of the partners runs his farm under organic certification (AB, the French organic label).
Organic farming rules require livestock effluents to come from non-industrial farms. The same applies to digestate.
Digestate from anaerobic digestion is allowed in organic farming, on the sole condition that no input is industrial.
This is the case for the La Chapelle-Neuve project, whose strength lies in controlling its inputs, all of which come from the partners’ own (non-industrial) farms. No partnership with industrial companies is possible or planned: this guarantees a local, 100% agricultural project.
This self-sufficiency in inputs is a guarantee of economic security for the banks financing the project.
The natural process of on-farm anaerobic digestion is carried out by micro-organisms naturally present in livestock effluents.
The process, which lasts more than 80 days at 40 °C, mineralises the organic nitrogen in the effluents.
It is expected to cut by 75% the chemical or fossil fertiliser inputs needed for plant growth.
Studies on the agro-ecological performance of anaerobic digestion (in French)
Why is the site located in La Chapelle-Neuve (Morbihan)?
Slurry is the only pumpable agricultural material that enters the digestion process. By building the site at Kériven, in La Chapelle-Neuve, we reduce the carbon footprint of slurry transport. Simon’s site no. 1 provides 40% of the effluents produced daily by the dairy farms, about 10 t/day, which enter the process without any transport. In other words, 22% of the total volume of inputs needs no transport at all.
Thanks to this location, the site avoids 213 slurry transports a year.
The production site is ideally central, both to the slurry flows and to the various fields farmed by the partners.
As a result, a tonne of effluent travels only 5.1 km on average to reach the process, compared with 9.3 km for a CIVE (an intermediate crop grown for energy).
On an annual average, 5.40 trips per working day serve the site to deliver effluents or CIVE, or to take away digestate.
The two founding farms of the project generate 2.02 trips per working day, none of them through the village centre.
We thus produce 846 kWh per kilometre of effluent transported, for a diesel consumption of 10 kWh/km. In other words, the ratio “renewable energy produced / fossil energy consumed” is 85 for effluents: 1.2% fossil energy for 100% renewable energy produced.
For CIVE, the ratio is 264: 0.4% fossil energy for 100% renewable energy produced.
The project (La Chapelle-Neuve had 979 inhabitants in 2022) includes installations that comply with the regulatory distances from neighbouring properties.
What about farm odours?
As part of its commitment to anaerobic digestion, TiNERZH carried out a baseline odour study around the future site at La Chapelle-Neuve, an area with a long farming history. The study recorded the typical smells of the countryside linked to farming activities.
A comparative study will be carried out once the 100% agricultural unit is in operation, to guarantee that the local olfactory identity is preserved. Residents will be able to see that odours stay the same, since the inputs will be the same as those already found on the surrounding farms.
The Biogaz de la Vilaine digester, near Chavagne (4,268 inhabitants in 2020) and the river Vilaine, has been operating since 2021 without any nuisance reported by local residents.
What measures protect the environment?
The production site is planned on land outside the catchment area that includes a protected biotope.
In line with regulations, the ground beneath the tanks will be sealed to prevent any leak. The best available technique (BAT) chosen for this sealing will be presented to the competent authorities. No uncontrolled discharge can therefore reach the environment.
To guarantee safety and protect the environment, the project includes strict measures. The tanks will be fitted with double safety valves equipped with position sensors. During each withdrawal of digestate for spreading, a safety device requires the prior closure of two valves, upstream and downstream of the lagoon that treats contaminated rainwater: both closures are required before the tanks can be opened. An automated system monitors the safety sensors and supervises the whole loading process. In the event of a leak, manual valves, which back up the automatic ones, are closed pending pumping and treatment. Any risk of pollution is thus eliminated.
Management and maintenance procedures will regularly check that the sensors and valves are in good condition and working order.
By combining strict dispatch procedures with advanced control systems, our site will be safe and can serve as an example of environmental protection.
Environmental safety is not optional. It calls for no compromise. Our priority is therefore to put in place protective measures that guarantee the safety of people, ecosystems and the planet as a whole.
Odourless digestate will replace traditional slurry, continuing the responsible practices already in place for spreading cattle slurry. In line with earlier regulatory commitments, this approach aims to preserve biodiversity, in particular the freshwater pearl mussel. The spreading limits set in 2021 will continue to be strictly applied, to protect water, soils and all living things.
What jobs for the area?
The project will directly employ 2 people at the TiNERZH site. Three more jobs will be shared between the CUMA de l’Evel (a farm machinery cooperative) and the agricultural contractor ETA Thomas FRANÇOIS, for sowing and harvesting CIVE and transporting effluents and digestate.
During construction, 18.8 full-time equivalent (FTE) staff will be employed for one year.
The project thus creates 5 local jobs that cannot be relocated.
An on-farm digester with no effect on property prices
A 2020 study by Quelia, with Artelia and Segat, shows that building on-farm digesters has no effect on the nearby property market.
To read the brochure or the full study (in French): 2050.eco/immobilier, or scan this code.
To help the site blend into the landscape, the project includes planting hedgerows and trees, which will improve its visual integration while storing carbon.