Giving waste a new life in Saint-Malo

Key figures

1

year of renovation work

25,000

metric tons of waste treated per year by UTOM

8,000

metric tons of compost produced per year

Saint-Malo Agglomération intercommunal authority (SMA) launched a project to revamp its old household waste treatment plant in 2009. After one year of renovation work contracted to CNIM in 2010, the new facility was officially handed over in 2012. The principal aim was to optimize the plant’s compost sanitary quality in compliance with new NFU 44-051 standards and recommendations from the CERAFEL regional fruit and vegetable growers’ association. Achieving this goal has reinforced a close partnership with the Terres de Saint-Malo producers’ group comprising some 100 fruit and vegetable growers whose products are marketed under the Prince de Bretagne brand.

The Saint-Malo household waste treatment plant (UTOM) handles about 25,000 metric tons of waste per year. The organic fraction, representing 50% of that household waste, and some of the green waste collected for processing is composted (making a total of about 8,000 metric tons a year). Saint-Malo Agglomération chose CNIM to bring its household waste treatment plant, built in the 1980s, into line to new standards. CNIM recommended installing a special composting and organic waste recovery system.

4 to 6 week’s fermentation

The waste is deposited in a large cylinder, known as a stabilized bioreactor, the core element of the composting unit. In a pre-fermentation stage tube which is continuously rotated for three days at a temperature of 60°C, the organic parts of the waste are broken down, leaving only a small fraction of the initial waste. Metals, glass, inert material and plastics are then separated from the organic matter during a refining stage. This type of refuse, which represents less than 50% of the original waste entering the system, is then to the Taden plant for waste-to-energy treatment. Before the start of a two-stage composting process, the fermentable waste is mixed with shredded green waste in order to help the circulation of air. For four to six weeks, this mixture is kept in fermentation tunnels where temperature, hygrometry and oxygen concentrations can be monitored and regulated. After being turned over, the mixture completes its aerobic decomposition phase in designated storage areas for a further three to four weeks. After sifting, the end product is then kept on a storage platform for several months before use.

Compost used by about 100 local fruit and vegetable growers

Saint-Malo Agglomération now produces high-quality compost complying with new standards (NFU 44-051) and recommendations from the CERAFEL regional fruit and vegetable growers’ association. Saint-Malo Agglomération has a close partnership with the Terres de Saint-Malo producers’ group comprising some 100 fruit and vegetable growers whose products are marketed under the Prince de Bretagne brand.

UTOM marked the occasion of European Sustainable Development Week when it welcomed visitors to its annual open day on June 3.