22% of French ski areas meet this criteria
Anaerobic treatment (oxygen-free) allows fermentation of sludge from wastewater treatment plants. The quantity of sludge is reduced and methane that can be used for domestic heating is recovered.
Direct anaerobic digestion of sludge from wastewater treatment plants involves about one third of the sludge produced in France, or the equivalent of 20 million inhabitants. The advantage of an anaerobic process in the mountains is obvious: anaerobic treatment allows the reduction of dry matter by 50% while creating heat or electricity!
The reduction of wastewater treatment sludge is a priority because large quantities make recycling difficult, specifically in the peak holiday periods in the ski areas.
What can be done with this sludge? The aim of anaerobic treatment is to reduce the amount of sludge produced and create energy in the form of reusable gas (carbon dioxide and methane). A very advantageous solution to reduce wastewater treatment sludge.
Gases recovered by using this process do not participate in the greenhouse effect since the methane that is produced is used to generate electricity or heat. Without anaerobic digestion, these gases would be released into the atmosphere with a direct impact on climate and would not produce energy
How does it work?
The process is the following: micro organisms digest the solids contained in the water. They release CO2 (carbon dioxide) and CH4 (methane), which is stored to be reused, e.g.: in the form of heat or electrical energy. The digestion residue (or digestate) is stable, deodorised and mostly pathogen-free. The anaerobic digestion is the biological process that allows for the production of methane from organic (and sometimes mineral) waste. During its production, methane is mixed most of the time with carbon dioxide and other gases in small quantities. This mixture is called a Biogas.
Methane is energy-intensive: 35 MJ/m³ (10 kWh/m³)
Anaerobic digestion is a 100% natural process. Here are a few natural examples:
Mountain region specificities
In the mountains, sludge treatment often creates a problem. Not only in terms of quantity, but in terms of quality as well. Anaerobic treatment reduces the quantity of dry matter and makes it possible to provide true green energy for ski areas.
A concrete example: the Abbaye de Tamié, which processes 4000 litres of milk per day, produces 17 m3 of effluents or 290 kg of COD* per day. An aerobic post-treatment allows the reduction of this COD pollution and the biogas produced is burnt to provide hot water to the monastery.
The biogas that is produced makes it possible to feed a 40-kW burner for additional heating of the premises.
My resort was awarded this logo if:
The resort collects biogas and treats its sludge with an efficient system. The sludge can be treated and transformed into compost to be spread over the ski slopes. The resort is also equipped with a methane collection plant and takes advantage of its biogas to heat building or other local offices. It may also opt for another sludge reducing system such as: fungi, reeds, lagoons etc. In this case the sludge will be composted and certified.