Adding treatment capacity to an existing wastewater treatment plant does not always require costly facilities expansion. In many cases, process modifications that make more efficient use of existing facilities are feasible. At the 10-mgd Camp Creek Water Pollution Control Plant in Fulton County, Ga., two parallel activated sludge trains were converted into a single sludge reaeration process for a cost-effective plant upgrade without expansion. One aeration tank was converted to a contact tack, and the other to a reaeration tank.