Dung has sweet smell of success

A plan to get rid of farming smells caused by cow dung in a tourist area has worked

The clever concept has given farmers extra revenue as the dung is turned into biogas and used to make electricity that they can sell to the national grid.

It has also made fertiliser for their fields and created enough power to run a dairy unit and three homes.

The méthanisation plants set up by Dordogne farm cooperatives use anaerobic digestion to turn dung into biogas and biofertiliser.

So far, five plants have been set up by Dordogne Chamber of Agriculture and Asseldor, the department association of livestock farmers with 15 million kilowatt hours (kWh) being generated each year – that is enough for the non-heating needs of 2,600 homes.

Anaerobic digestion, méthanisation in French, uses bacteria to break down cow dung in oxygen-free chambers set up on farms, producing methane and carbon dioxide. Methane biogas can be used for heating, to generate electricity and, after treatment, as natural gas to boost the mains gas network, or as biofuel for cars.

The solid residue can be spread on to the fields as fertiliser and, vital for neighbours and visiting tourists, it smells better than untreated manure.

It is good for the environment, too, as the methane given off by the dung is a powerful greenhouse gas.

Dordogne has seen anaerobic digestion plants installed at a rate of one every two years after initial funding by Casdar, a government scheme to provide funding for the development of agriculture.

However, it was expensive for the pioneers such as the Marcillac-Saint-Quentin collective. Julien Michau, environmental department head at Dordogne Chamber of Agriculture, said: “It’s a big investment for farmers, they might not see a return until 11-12 years later.”

The decision to locate anaerobic digestion plants within farming collectives cuts down on transportation costs and keeps everything local, while offering the farmers the possibility of extra revenue.

The Chambre d’Agriculture sees the added attraction of allowing a mentoring system where the first farmers to use the system offer advice and support to those who follow afterwards. In practice, the pioneers have become energetic promoters of the scheme.

The key aim was to cut smells in a tourist destination and a protected zone and the first anaerobic digestion unit was built in 2010 and was up and running a year later.

Bacteria used in the process give off heat and this gives hot water for milk production and powers farm homes while also helping off-set installation costs – and all before the biogas is sold to EDF.

Mr Michau said: “The project is a great adventure. It’s not like solar panels, which basically run themselves. Anaerobic digestion creates extra work, and requires the farmers to supply the raw materials.

“But it has great potential. The technology will evolve and become available in smaller units which are more affordable. I’d recommend it.”