A bit of a bad atmosphere

At around 11.00 am, trucks drive onto the site every minute and unload the biowaste they collected in the morning. Around 27,000 tonnes of food waste, off-spec batches from the food industry and packaged food pass through the Bakona biogas plant outside Itzig every year. Jean-Pierre Nau, farmer and managing director of the company, leads us to the centre of the farm. From here you have a good overview of the individual stations of the plant.

The first work step: foreign matter such as plastic bags must be sorted out. Nau speaks of a proportion of five to seven per cent of inert materials. They later end up in the waste incineration plant in Leudelingen. Kitchen, canteen and restaurant waste is then exposed to a temperature of 70°C for an hour to kill bacteria. That is the regulation. After that, a worker with a shovel mixes the mass with renewable raw materials.

On this morning at the end of January, it is tobacco dust, a waste product of the cigarette industry, and grass. 8,000 tonnes of agricultural biomass go into the plant every year, in addition to the biowaste. This includes maize, which is grown for use in biogas plants and brings "stability" to the fermentation process. The mixture is then fermented in a ratio of 3:1 (70 to 75 per cent organic waste). In the fermenter, bacteria break down the organic matter. The resulting biogas is upgraded to biomethane and then fed into the natural gas grid. "Our goal is to have the facility running on 100 per cent organic waste, " Nau explains. Whether that is achievable is another matter. But more on that later.

The remaining fermentation residues are separated into a solid and liquid phase, as in the case of manure separation, and are returned to the field as fertiliser. The advantages for water protection have already been explained in another Journal paper.