County plant could treat sewage from cruise ships

Sludge from the sewage produced by 750,000 cruise-ship passengers who visit Seattle each year could be piped to King County's Renton sewage-treatment plant and treated there, a county study has concluded.

Most ships now dump those solids at sea.

The piping system would cost $3 million, according to the Wastewater Treatment Division study, which didn't calculate how much it would cost cruise-ship companies to connect to the pipeline. The Renton treatment plant would not have to be enlarged.

The Metropolitan King County Council, which called for the study last spring, passed a motion Monday calling for further discussions with cruise-ship operators, the state Department of Ecology and the Port of Seattle.

"This study shows that we can do better for Puget Sound," Councilmember Larry Phillips, sponsor of the motion, said in a written statement. "... Puget Sound should be as clean, productive and protected in reality as it appears to tourists visiting us on cruise ships."

Cruise ships typically generate 35 tons of sludge from sewage each day, according to the county study. Most ships currently dump that waste in the water, at least 12 miles from shore while traveling at least six knots.

If treated at the county's Renton plant, the "biomass" from ships would be recycled on farms and in forests.

The county report said more study is needed to determine how to control odor while waste is being transferred from ships to county pipelines.

The report did not estimate how much it would cost to truck solid wastes to Renton, an option the authors expect will be explored by Ecology, the port and the cruise industry.

Ships with advanced treatment systems are allowed to discharge liquid waste in Puget Sound, while vessels with less advanced systems must dump the waste farther from shore.

Keith Ervin: 206-464-2105 or kervin@seattletimes.com