Landfills are the primary method of waste disposal in many parts of the world, including United States and Canada. Bioreactor landfills are expected to reduce the amount of and costs associated with management of leachate, to increase the rate of production of methane (natural gas) for commercial purposes and reduce the amount of land required for land-fills. Bioreactor landfills are monitored and manipulate oxygen and moisture levels to increase the rate of decomposition by microbial activity.
Traditional landfills and associated problems
Landfills are the oldest known method of waste disposal. Waste is buried in large dug out pits (unless naturally occurring locations are available) and covered. Bacteria and archaea decompose the waste over several decades producing several by-products of importance, including methane gas (natural gas), leachate, and hydrogen sulfide (H2S), N2O2, etc.).
Working of a bioreactor landfill
There are three types of bioreactor: 
In aerobic bioreactors air is pumped into the landfill using either vertical or horizontal system of pipes. The aerobic environment decomposition is accelerated and amount of VOCs, toxicity of leachate and methane are minimised. In anaerobic bioreactors with leachate being circulated the landfill produces methane at a rate much faster and earlier than traditional landfills. The high concentration and quantity of methane allows it to be used more efficiently for commercial purposes while reducing the time that the landfill needs to be monitored for methane production. Hybrid bioreactors subject the upper portions of the landfill through aerobic-anaerobic cycles to increase decomposition rate while methane is produced by the lower portions of the landfill. Bioreactor landfills produce lower quantities of VOCs than traditional landfills, except H2S. Bioreactor landfills produce higher quantities of H2S. The exact biochemical pathway responsible for this increase is not well studied 
Advantages of bioreactor landfills
Bioreactor landfills accelerate the process of decomposition. As decomposition progresses, the mass of biodegradable components in the landfill declines, creating more space for dumping garbage. Bioreactor landfills are expected to increase this rate of decomposition and save up to 30% of space needed for landfills. With increasing amounts of solid waste produced every year and scarcity of landfill spaces, bioreactor landfill can thus provide a significant way of maximising landfill space. This is not just cost effective, but since less land is needed for the landfills, this is also better for the environment.
Furthermore, most landfills are monitored for at least 3 to 4 decades to ensure that no leachate or landfill gases escape into the community surrounding the landfill site. In contrast, bioreactor landfill are expected to decompose to level that does not require monitoring in less than a decade. Hence, the landfill land can be used for other purposes such as reforestation or parks, depending on the location at an earlier date. In addition, re-using leachate to moisturise the landfill filters it. Thus, less time and energy is required to process the leachate, making the process more efficient.
Disadvantages of bioreactor landfills
Bioreactor landfills are a relatively new technology. For the newly developed bioreactor landfills initial monitoring costs are higher to ensure that everything important is discovered and properly controlled. This includes gases, odours and seepage of leachate into the ground surface.
The increased moisture content of bioreactor landfill may reduce the structural stability of the landfill by increasing the pore water pressure within the waste mass. 
Since the target of bioreactor landfills is to maintain a high moisture content, gas collection systems can be affected by the increased moisture content of the waste.
Implementation of bioreactor landfills
Bioreactor landfills being a novel technology are still in the development phase. Pilot projects for bioreactor landfills are showing promise and more are being experiment with in different parts of the world. Despite the potential benefits of bioreactor landfills there are no standardised and approved designs with guidelines and operational procedures. Following is a list of bioreactor landfill projects which are being used to collect data for forming these needed guidelines and procedures:
- Yolo County
- Alachua County Southeast Landfill
- Highlands County
- New River Regional Landfill, Raiford
- Polk County Landfill, Winter Haven
- Outer Loop Landfill
- Saint Clair County
- Plantation Oaks Bioreactor Demonstration Project, Sibley
- ACUA's Haneman Environmental Park, Egg Harbor Township
- Buncombe County Landfill Project
- Maplewood Landfill and King George County Landfills
- Virginia Landfill Project XL Demonstration Project
- Sainte-Sophie Bioreactor demonstration Project, Quebec
New South Wales
- WoodLawn, Goulburn
- Ti Tree Bioenergy, Ipswich
- The Hinkley Center For Solid and Hazardous Waste Management, The Department of Environmental Engineering Sciences, University of Florida, The Civil and Environmental Engineering Department, University of Central Florida. (2008). Florida Bioreactor Landfill Demonstration Project: Executive Summary. Retrieved February 03, 2010, from 
- Christensen, T. H. (1999). Landfilling of waste: Biogas
- Washington State Department of Ecology. (n.d.). Solid Waste Landfill Design Manual. Retrieved February 3, 2010, from 
- Kjeldsen, P. M. (2002). Present and Long-Term Composition of MSW Landfill Leachate: A Review. Critical Reviews in Environmental Science and Technology , 297-336.
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- Hinkley Center For Solid and Hazardous Waste Management. (2006). Bioreactor.org - General Info. Retrieved February 3, 2010, from Bioreactor.org: 
- Murphyb, S. R. (1992). A lysimeter study of the aerobic landfill concept . Waste Management & Research , 485-503.
- Reinhart, Debra R., and Timothy G. Townsend. Landfill Bioreactor Design and Operation. Boca Raton, Fla: Lewis, 1998. Print.
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- Kjeldsen, P. M. (2002). Present and Long-Term Composition of MSW Landfill Leachate: A Review. Critical Reviews in Environmental Science and Technology , pp. 297-336
- Toward a Twenty-first Century Landfill - Yolo County's Bioreactor Research Project web page.