State and local officials gathered at Suffolk County’s Forge River wastewater treatment plant Monday to announce the facility is now in operation and serving the first 10 of what will eventually be 1,900 homes and businesses in the Mastic-Shirley area.

Suffolk County Executive Ed Romaine, County Legislator Jim Mazzarella and acting state Department of Environmental Conservation Commissioner Amanda Lefton were among the officials who announced the completion of the $228 million plant, which will treat wastewater from area homes and businesses that will be connected to sewer lines, helping to reduce nitrogen runoff into the Forge River. The plant was funded by federal dollars from Superstorm Sandy relief.

Mazzarella, who represents the area, called it “a great day for the Forge River,” a sentiment that Lefton echoed.

She called the plant’s opening “a major milestone” in the effort to protect Long Island’s water supply.

“Having grown up here [on Long Island], I know how important clean water is to Long Island communities,” Lefton said.

County Public Works Commissioner Charles Bartha said the plant is the first wastewater treatment plant built in the county in decades.

“But not the last,” Romaine said.

Romaine said the county expects to spend at least $1 billion on sewer expansions in the next three years. Voters in November overwhelmingly approved a one-eighth cent increase in the county sales tax for the next 35 years to build new sewers and provide grants to homeowners to replace aging septic systems and cesspools with nitrogen-removing septic systems.

The Forge River plant can handle 1 million gallons of wastewater per day, Bartha said. The plan is to increase the plant’s capacity by an additional 450,000 gallons per day, he said.