The household waste recycling centre (HWRC) in Assens, Denmark is located on top of an old landfill, which produces the climate-deteriorating gas methane. A new bio-cover made of composted garden waste transforms the methane into carbon dioxide, which is far less harmful to the climate.
Although it was a long time ago landfills served as dump stations for organic waste, Assens Utility in Denmark has discovered that a significant amount of the greenhouse gas methane is still being disseminated from the site, caused by the transition of the organic waste, which was previously dumped at the landfill and covered by soil.
To decrease the emission, Assens Utility has with NIRAS as their consultant built a 2,000 square meter bio-cover based on composted garden waste from their own production. Where the methane previously seeped through the ground and into the atmosphere, the plant now collects and leads the produced methane from the landfill to the bio-cover. Here, the natural microorganisms in the compost transition the methane into carbon dioxide and water.
NIRAS has consulted on the bio-cover solution, and according to Senior Consultant Søren Dyreborg, a bio-cover is one of the most socioeconomic methods in terms of achieving a great climate effect on a small budget.
“If it is not economically feasible to establish a gas collection system for a landfill that emits methane, a bio-cover is the obvious solution to reduce the amount of emitted methane from the landfill. A bio-cover is a passive system that is more or less self-sufficient, in contrast to a pumping station, which often needs servicing,” Søren Dyreborg says.
Prior to constructing of the bio-cover, environmental engineer Rune Emil Jacobsen from NIRAS executed surface measurements, which identified the areas that emitted the largest amounts of methane. Total measurements performed by FORCE Technology furthermore revealed that the previous landfill had a total emission of 7.5 kg methane per hour.
After the bio-cover was established, new total measurements were performed. The results showed a 60 per cent reduction in emissions, which is congruent with what was hoped for according to the initiatives implemented in the most crucial emission areas.
“Experiences from other landfills indicate that it is possible to reduce the emission significantly. The result, however, depends heavily on the ways in which the emission occurs, how the landfill is designed, what it is used for, and the practical conditions of the landfill,” Søren Dyreborg says.
“We are very happy that the bio-cover allows us to utilize our own compost waste as a medium for bacteria, which decompose the powerful greenhouse gas methane through oxidisation into carbon dioxide, thus effectively reducing our emissions. We are simultaneously happy to contribute to Assens Municipality’s strategy to decrease the emission of greenhouse gasses, and being ahead of the national goals for the green transition towards 2030,” says operations- and waste director Søren Rasmussen from Assens Utility.
NIRAS has been in charge of bio-covers at several other landfills, and the technology itself has knowhow potential in terms of our neighbouring countries and the rest of Europe, Søren Dyreborg assesses.
“After The Danish Environmental Protection Agency’s subsidisation of establishing bio-covers, Denmark has gained substantial expertise in the area,” Søren Dyreborg says and continues:
“Now it is only a question of whether the rest of Europe will follow in Denmark’s green footsteps.”