Landfill recirculation is a practice that divides opinion. It is the process of repeatedly reapplying leachate to the waste mass in a landfill. Landfill recirculation can save offsite disposal costs and boost gas production (for those landfills that harvest methane gas), but it can also oversaturate the waste mass and trigger additional problems.
Landfill recirculation can work in certain cases, especially when the company running the site is aware of the potential problems that can arise and acts before they do. Landfills that have no sewer connections, or spend a lot of money transporting leachate to other facilities, could benefit from recirculating their leachate onsite. This can be particularly beneficial to landfills with dry waste.
Landfill recirculation can boost methane production
This practice can boost methane production by at least 20 percent, improving the waste-to-energy efficiencies of these facilities. The methane gas is also more concentrated as a result of leachate recirculation. The practice of landfill recirculation was first introduced in the 1970s in the United States. However, it was largely rejected due to the lack of systems to contain and remove the leachate.
In the 1990s, some US states began to play around with landfill recirculation once again. The theory was that recirculation would speed up the decomposition of waste materials and increase the density of the mass. This would allow landfills to collect more waste over time. While partly true, the negative side effects of landfill recirculation also came to light.
Downsides to landfill recirculation
“Unfortunately, it has not always been done responsibly, and in some instances, creates problems. For instance, if you oversaturate the waste, you can get liquid in the gas wells, impairing the gas collection system,” explains senior vice president of Civil & Environmental Consultants Inc., Steve Menoff.
“You can have leachate seeps and breakouts, stability issues and odor problems. There is a fine line and it has to be done in phases from one cell to another cell,” he adds. If landfills are unable to contain these leachate breakouts, the resulting effects could be severely harmful. Groundwater and rivers can be contaminated, affecting nearby farms and communities.
Controlling leachate in landfills
There are ways to manage the leachate in landfills and prevent it from escaping. Using recycled tyres and glass to separate the layers of waste mass can help to spread leachate more evenly. “These materials (recycled glass and rubber) are spread across the landfill surface. A pipe is placed inside this drainage layer of materials and waste is placed on top. So, tire shreds and glass cullets are a sandwich between garbage layers, enabling more even leachate distribution,” says Milind Khire, an environmental engineering professor and researcher at the University of North Carolina.
The tyres and glass will help to spread the leachate across a wider surface area in the landfill. This is a cost-effective solution that has been used in various landfills around the world for many years. Khire first trialled this system in 2003 when he built three test layers – one using runner, one with glass and one with geocomposite. Glass proved to be the most efficient material, followed by recycled rubber. The geocomposite was not as effective.
Landfill recirculation has saved millions of dollars for those sites that practice it effectively. However, successful recirculation lies in just that – effective processes and an ability to control the leachate before it creates additional problems. Dry waste landfills can benefit from adding more leachate to the waste mass, but the company needs to keep a close eye on moisture levels.
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