Municipal waste landfills typically generate a range of impacts caused by a number of elements: size, traffic, dust/litter, leachate generation, gas production and gulls or other vectors. To reduce th...
Municipal waste landfills typically generate a range of impacts caused by a number of elements: size, traffic, dust/litter, leachate generation, gas production and gulls or other vectors. To reduce these impacts, a new type of landfill has been developed, called the “stabilized” landfill. Stabilized landfills use mechanical-biological treatment (or “MBT”) to treat solid waste before landfilling; they’re being promoted as an alternative to thermal treatment and traditional landfill.
A stabilized landfill differs from traditional landfills because it:
*Mechanically screens waste to remove materials that should not be landfilled (i.e., recyclables, HHW) and to remove materials such as plastic that can’t be stabilized.
*Biologically treats waste to reduce landfill gas and leachate production.
The MBT systems mean that the first stage of a stabilized landfill isn’t a landfill at all. Instead, it’s much closer to a combined recycling and composting (or anaerobic digestion) facility. Once the waste materials are treated, the stabilized waste is landfilled in a traditional type of landfill.
A European Union directive requiring organic material to be treated before disposal has driven the construction of both stabilized landfills and waste to energy (WTE) facilities throughout Europe. Even some WTE plants have started stabilizing the wet organic fraction of their feedstock because of its poor fuel value.
Only one stabilized landfill exists in North America — in Halifax, Nova Scotia. Halifax’s landfill was constructed after a series of failed attempts at siting traditional landfill and WTE facilities. Following a community driven process, the region determined that a landfill could be sited under the conditions that source-separated organics and recycling programs be implemented and that remaining waste be stabilized before landfilling.
While the concept of stabilizing the waste seems simple enough, there are a number of variations:
1. Feedstock: Some have full source-separation programs, including organics, while others do not. This can impact the level of processing required. It’s especially important to remove PVC materials for those that produce a refuse-derived fuel (described below).
2. Level of processing: The level of processing ranges from low to high. Halifax’s stabilizing process is at the lower level because it composts the organic fraction of the waste for only about 21 days before landfilling. Others stabilize the waste for up to six months. Higher levels of processing result in lower gas production and lower leachate strength than for those that process a shorter period of time.
3. Biological processing: Some stabilized landfills use aerobic composting processes while others utilize anaerobic processes to stabilize the material. The main difference is that anaerobic processes can capture energy in the form of methane gas. The end result (stabilized waste) is the same.
4. Refuse Derived Fuel (RDF) production: Some stabilized landfills, particularly those in Germany, separate “high energy” plastics from the organic components of the waste. The organic portions are still stabilized and landfilled. The plastics are separated, dried and sent to other facilities as RDF. The difference between this RDF and traditional mixed municipal waste is that the RDF is much more homogeneous, resulting in higher energy recovery and lower requirements for emission control than traditional WTE facilities. Of course, the major bonus for a municipality is that it doesn’t have to invest in high-cost WTE plants.
While the cost for stabilizing material doesn’t come cheap — it can double the cost of a landfill — in Europe it’s usually less than the cost of a modern thermal treatment plant. It should also be noted that long-term savings from stabilized landfills in the form of reduced greenhouse gas production and lower treatment of landfill leachate hasn’t been fully quantified — because stabilized landfills haven’t been around long enough to determine long term savings. But intuitively one knows that gas and liquid generation will be very low.
Proponents of stabilized landfills point to one of the biggest benefits: flexibility. Traditional WTE plants are not tolerant of big changes to the waste stream — either the energy value or the volume. Stabilized landfills can tolerate considerable changes in both.
Of the six main elements that define landfill impacts today, a stabilized landfill will substantially lessen the impact of landfill gas, leachate production, gull control and after-care (in the form of settlement from decomposition). Those that produce RDF also lessen litter impacts at the landfill.
To a municipality considering disposal options, experts point out three main significant benefits for stabilized landfills over other options: lower cost, greater flexibility and, proven examples of successful facilities.
In the end, though, reduction, reuse, recycling and composting still provide the greatest environmental and social benefits, reducing the need for disposal facilities altogether.