Have you heard of a bioreactor landfill?
A bioreactor landfill, is one in which liquid is added in an organized manner to speed decomposition of the waste. Maintaining the moisture level inside the landfill accelerates the natural microbiological process. The microbes decomposing the waste can be aerobic, anaerobic, or a combination of both. If aerobic microbes are being promoted, then air, as well as liquid, is injected into the landfill.
This means the waste compacts faster, making room for more waste than a traditional landfill of the same size. What's cool too, is that research suggests that bioreactors may create more landfill gasses, such as methane and carbon dioxide.
That doesn't sound good, but it does have benefits.
This excess methane can be recovered, and used to produce electricity. Also, the increased emission of methane from bioreactor landfills may make recovery of methane more cost effective than it is with present landfills.
As for disadvantages, the increased moisture in bioreactor landfills means they require more monitoring during their active lives than traditional landfills. This also makes them more costly during their active lives.
Bioreactors have to be monitored carefully for factors such as escaping liquid, and controlled for factors such as increased odors. They require less monitoring after closing, though, and in the long run, may cost less than traditional landfills.