From waste product to valuable fertilizer

Anyone who wants to enter the anaerobic digestion plant has to be a bit brave. Because here in Mondercange, trucks deliver the contents of organic garbage bins from dozens of municipalities. Banana peels, apple pulp, coffee grounds, spoiled cheese and meat products, and grass: tons of food scraps and kitchen waste end up at the Minett-Kompost syndicate every day. A magnet first pulls out metallic objects that have strayed into the organic garbage cans. Then the mixture is coarsely shredded. "The goal is to open the plastic bags without pulverizing them", says François Delion, describing the process. The intense odor has not bothered the plant manager for a long time. "I don't smell it anymore", he says, laughing.

What we as consumers often want to see disposed of as quickly as possible is a valuable resource for Minett-Kompost. The contents of the organic garbage cans are sorted into two fractions in a drum screen. Everything smaller than 80 mm ends up in the digester. You can imagine it as a large, dark chamber. For about three weeks, a large number of bacteria decompose the waste at just under 40° Celsius and in the absence of oxygen, turning it into biogas. What remains is a brown mass called digestate. The water is removed from this digestate by pressing. The mass is then mixed with branches and hedge cuttings – anything larger than 80mm – to produce compost. Which can then be used without hesitation in the field, in nurseries or in private gardens.

Following a pilot project, 16 municipalities established the Minett-Kompost syndicate in 1993. Four years later, the composting plant in Mondercange was put into operation, supplemented in 2011 by an anaerobic digestion plant. To date, the plant has transformed around 35,000 tons of organic waste (garden and kitchen waste) into biomethane, compost and wood chips per year. This year, and in the future, that will increase significantly. Jerry Clement expects that the municipality of Luxembourg will officially join in 2022. Already this year, the plant has had to handle more than 40,000 tons because the Sidec waste syndicate, with its 46 member municipalities in the north of the country, delivers about 7,000 tons through a convention.