. This second step in the process utilizes scrubbers and filter presses. A primitive version of the FGD process has been in existence for more than 150 years and was firstused in England in the 1850’s. The use of FGD, on a large scale, was not used commercially untilthe 1970’s. This rise in the use of FGD technology came about with the passage of the Clean Air Act of 1963 which was the first attempt to control air pollution. Since it’s inception, the Clean Air Act has been amended to impose stricter and more specific regulations, such as Title IV in 1990. Title IV ordered the lowering of SO2emissions by 10 million tons under the 1980 levels. Title IV also established the Acid Rain Program (ARP) which required a reduction of chemicals known to contribute to acid rain. These combined regulations set a cap on the total amount of pollutants that can be emitted by power plants. One way of battling SO2emission levels is through the FGD process.FGD is a two-step process where fly ash is first removed followed by the removal of SO2.The second step of the process consists of the combustion gases passing through a scrubbing system. The Environmental Protection Agency estimates that, 85% of FGD systems operating in the United States are wet scrubbing systems. Wet scrubbing systems utilize a limestone slurry, injected into a chamber, which allows the calcium in the limestone to react with the SO2in the flue gas. Wet scrubbing systems are preferred when the sulfur content of the coal being burned is greater than 2%. In its basic form the FGD process consists of four steps including scrubbing, clarification, sludge holding and dewatering. Dewatering and filter presses play an important rolein eliminating SO2from the exhaust gases.