Problem
Over the past 200 years the concentration of methane gas (CH4) has more than doubled. Land fills account for 11.4% of methane emissions in the United States. The methane gas is of concern because of its explosiveness in air and its contribution to the greenhouse gas affects. Methane production has even increased at a rate higher than that of carbon dioxide as seen in figure P-1 below.
Figure P-1. Methane Production vs. Carbon Dioxide Production
Landfill gas is produced throughout the life of a landfill. The gas is the result of the biological degradation of organic waste deposited into a landfill. Landfill gas contains 45-60% methane, 40-60% carbon dioxide, and small quantities of other gasses and compounds (nitrogen, oxygen, sulphides, ammonia, hydrogen, carbon monoxides and trace constituents). The methane produced from the landfill is the result of anaerobic degradation of organic matter in the landfill waste. The production of landfill gas is dependent on many factors. The gas production depends on the type of waste in the landfill and its moisture content, the local climate (temperature and rainfall), and the type of leachate collection system. The volume and composition of landfill gas produced varies as the waste undergoes distinct stages of degradation. The methanogenic stage is the longest in duration. Under favorable conditions landfill waste can reach the methanogenic stage within two years of filling. The major part of landfill gas production is complete within twenty years.Methane gas has a damaging effect on the environment by aiding the greenhouse effect up to 25 times larger than that of carbon dioxide. However, there are several emission laws in the United States to control carbon dioxide emissions, but none for methane. The government has been closely looking at the problem and it is widely rumored that a methane emission control law will be passed in the next couple of years in order to regulate the methane emissions coming out of landfills. For all of these reasons, it becomes extremely important to design ways to reduce methane emissions from landfills.