A new development project in Denmark is to investigate and introduce a method where air is blown into old waste to increase the rate of decomposition. The purpose is to reduce the climate and environmental impact of the waste, which could otherwise potentially pollute the environment for over 100 years.
- SDG: #6, #12, #13
- SECTORS: Environment and Ecology
- COUNTRIES: Denmark
- CLIENT: AV Miljø
In collaboration with AV Miljø and the Technical University of Denmark (DTU), NIRAS is to demonstrate and evaluate the method known as Landfill Aeration on the basis of both laboratory work at DTU and a larger field trial at the landfill AV Miljø in Hvidovre, close to Copenhagen.
When rainwater seeps down through deposited waste, it may dissolve an array of harmful substances, resulting in what is called leachate. If unprocessed leachate is discharged into the environment, it can lead to pollution. With landfill aeration, atmospheric air is blown into the deposited waste, helping it to break down faster and permanently reducing the waste's climate and environmental impact as a result.
How the method works
In all its simplicity, the experiment means introducing extra air to the waste in the landfill. At the selected disposal site, 15 boreholes have been drilled and a large container with air compressor and valves set up in order to blow air through the boreholes into the deposited waste.
If the experiment goes as hoped, the microbacterial conditions will be changed so that the landfill emits less methane, produces less contaminated leachate and accelerates the decomposition of problematic nitrous compounds such as ammonium. It is also likely, therefore, to shorten the period needed for aftercare, i.e. the time that elapses from the landfill closure until it no longer constitutes an unacceptable climate and environmental impact.
What is leachate?
In an environmental context, leachate is rainwater that has seeped through deposited waste. As the water passes, substances in the waste dissolve so that the leachate becomes contaminated. Leachate from landfills with household waste contains high concentrations of biodegradable organic matter and ammonium. At modern landfills, the leachate must be collected and treated to prevent contamination of soil, groundwater and nearby surface water.
First large-scale project on Danish ground
Landfill aeration is a widely recognised method and has been used abroad for many years, but has yet to make its mark in Denmark. Environmental engineer in NIRAS, Lotte Fjelsted, who holds a Ph.D. in environmental technology, works with environmental impacts from landfills and gas emissions in particular. Lotte is one of the initiators behind the project and is looking forward to testing this method on a large scale in Denmark.
"No one has tested the method on an entire landfill site in Denmark. But we hope to prove that this method can be advantageously implemented at several other landfills in Denmark," Lotte explains about the project.
Lotte Fjelsted, civil engineer and Ph. D. in environment technology, NIRAS
Collaboration with DTU Sustain
In essence, the method is quite simple: you simply speed up the natural decomposition of the deposited organic waste. What is difficult is to adapt the method to Danish landfills and document and quantify how well the method works.
"To ensure the right research angle, we are happy to be undertaking this project in collaboration with DTU Sustain. With their knowledge, resources and data and our expertise in landfills and the environment, we can ensure that this development project will be able to contribute with knowledge that can benefit many more Danish landfills," says Lotte Fjelsted about the new project. The hope is to demonstrate that the implementation of landfill aeration is both environmentally and economically sustainable for many of our Danish landfills.
Great potential for the method in Denmark
At the end of March 2023, the first air was pumped into AV Miljø's large, modern landfill site at Hvidovre. The people behind the project are currently working on the fine-tuning of the facility, which became fully operational at the end of April. Here, the field trial will run on part of the landfill for a minimum of two years. If the method is proven at this Danish landfill, there is more than enough to be getting on with.
Today, fortunately, much less waste is dumped than used to be the case, but old landfill sites still haunt the climate and environment. Discharges from these sites have continued for many more years than expected, underlining the relevance of developing new methods to reduce gas emissions and leachate. One of the challenges is their discharge of ammonium through the leachate. It can, in fact, take a very long time before the ammonium discharges come down to an acceptable level.
According to the Danish Environmental Protection Agency, around 200 landfills/waste sites have been established in Denmark post 1974. Landfill aeration may prove to be suitable for reducing the climate and environmental impact of the waste at many of these sites.
The first results of the large-scale project are expected to be ready in a year's time.
A more scientific explanation of the process of landfill aeration
In normal circumstances, waste in landfills degrade under anaerobic (oxygen-free) conditions. Organic waste degrading under anaerobic conditions, forms landfill gas, which consists of methane and carbon dioxide (CO2 ). The carbon dioxide in the landfill gas is considered climate neutral, as it comes from a biological process, while the methane is considered a powerful greenhouse gas – 28 times more powerful than CO2 – and is not considered climate neutral, even though it also comes from a biological process. At the same time, methane also poses a risk of fire and explosion.
Among other things, the decomposition of nitrous waste results in the formation of ammonium, which is washed out of the landfill in the leachate. Ammonium is converted to nitrate and can thus become a problem as it contributes to the nutrient load in the environment. Indeed, the ammonium content of the leachate is one of the aspects that helps define when the aftercare of the landfill can be brought to an end.
Landfill aeration results in a shift in degradation conditions from anaerobic to aerobic (oxygen-rich). Aerobic decomposition does not produce landfill gas and the degradation is faster than anaerobic decomposition. This stabilises the waste at a faster rate, ultimately leading to an earlier end to the landfill aftercare.