Waste is a relatively inexpensive material, but there are some economic and environmental issues associated with its treatment that can make it unattractive for commercial use. For example, landfills are useful sources for methane, however, a continuous collection of methane can be an issue. Depending on the size of the landfill, single or multiple sources of collection points of methane need to be equipped and this will require building a care­fully designed methane collection infrastructure. Also, if a power plant is to be built on or near landfill, its size will depend on the amount of the con­tinuous methane supply from the landfill. Generally the size of the power plant will vary from 1 to 100 MW, a size that is not always most economical. Getting a local permit for such an operation can also be an issue. Landfill gas generally contains about 50 to 55% methane, remaining carbon dioxide, and some other trace materials including hydrogen, nitrogen, and the like. This gas cannot be transported by a natural gas pipeline, which generally contains about 95% methane, without a further purification and upgrading process. Such a process can be expensive.

Numerous localities (particularly on the East Coast) have used MSW to support local power needs. Like landfill gas, the size of such a power plant will depend on the amount and continuous supply of MSW. For these rea­sons, these plants are now largely located in densely populated areas where a significant amount of MSW can be easily transported to a common collec­tion point. An installation of a power plant using MSW as raw material in remote areas can be economically unattractive. The same principle applies to other kinds of waste such as rubber tires, agricultural and forestry resi­dues, and so on, where transportation to a central location can be very expensive. This problem is further compounded because of low mass and energy densities of cellulosic waste. Sizing and separation of waste mate­rials for a particular treatment technology can also become a significant economic issue.

The treatment of waste can also lead to significant environmental issues. Depending on the composition of waste, thermochemical treatment can lead to significant amounts of impurities in the exit gas or remaining solids. Both of these impurities need to be eliminated either by pretreating waste or puri­fying the gaseous product and solid streams. These processes can be expen­sive depending upon the nature and amount of impurities. The problem can be further compounded for a mixed waste.