CEDAR RAPIDS — Alliant Energy almost has finished converting to natural gas one of its four coal-burning power units in Cedar Rapids.

The conversion project at the Prairie Creek Generation Station is expected to be finished Friday. Company officials said the natural gas will burn cleaner than the coal, reducing carbon dioxide and mercury emissions into the air. In addition, the unit won't require Cedar River water for cleaning out the ash.

A decision on whether to convert the other three units to natural gas or retire the units isn't expected for years.

Alliant's Iowa entity Interstate Power and Light has been making major changes since reaching a $620 million settlement with the Environmental Protection Agency in 2015 for upgrades at seven power plants across the state, covering pollution and emission reduction.