A project to replace the chemical-disinfection system with an ultraviolet-light system at the Fairfax County government’s Noman M. Cole Jr. Pollution Control Plant in Lorton has earned an Envision Gold award from the Institute for Sustainable Infrastructure.

The $72 million project is one of many upgrades to the plant, which treats more than 40 percent of the county’s wastewater.

Following a detailed evaluation of alternatives, ultraviolet disinfection was selected to replace the sodium-hypochlorite system, which county officials say was complicated to operate, labor-intensive to monitor and expensive to maintain.