The gypsum used to make drywall comes either from natural
gypsum (quarried rock) or from a by-product of coal-burning
power plants. Guess which gypsum source is considered more
environmentally friendly? If you guessed natural gypsum, guess
again. Most green building enthusiasts prefer drywall made from
flue-gas desulfurization (FGD) sludge.
Because of Clean Air Act requirements, power plants burning
high-sulfur coal use scrubbers to remove much of the sulfur dioxide,
a component of acid rain, from their flue gas. The scrubbing
process results in the production of
22 million tons of FGD sludge a
year. Because landfill costs are rising,
coal-burning plants are under
pressure to find a market for their
FGD sludge, which can