(Image credit: City of Bellingham)

In Bellingham, Wash., the sidewalks are paved with toilets - 400 discarded porcelain thrones ground up in a mixture they call "poticrete."

The sidewalks were part of the Meador Kansas Ellis Trail Project in Bellingham, about 22 miles south of the Canadian border. The project is the first-ever to receive certification from the Greenroads Foundation, a non-profit group advocating for sustainable transportation infrastructure. The certification, which was bestowed this week, has 11 requirements and represents "a significantly higher level of sustainability than the typical road project of today," according to the group.

The sidewalk project cost about $850,000, which is about the same cost as using the typical gravel concoction. Recycled asphalt was also used and low-energy LED street lighting added to cut the power bill, Freeman Anthony, project engineer for the City of Bellingham Public Works, said.

The crushed ceramic came from the Bellingham Housing Authority's toilets. That group approached Anthony in early 2011 because they had just upgraded three large housing facilities and didn't know what to do with their 400 used toilets.

(Image credit: City of Bellingham)

Designed in 2010 with construction beginning in May 2011, the project took about four months to complete.

It was the first time Bellingham has used crushed toilets as sidewalk or any infrastructure, Anthony said. At least one other town has used toilets for public works projects. In Fort Collins, Co., toilets are crushed and recycled into road aggregate.

Anthony said the material was tested to make sure the correct amount would be poured and remain strong as a sidewalk. Initially, a 40 percent mixture of the ceramic material was used, but eventually 25 percent was determined to be the best amount with the remainder as asphalt and gravel.

There were at least two environmental benefits in using the recycled materials for the sidewalk, he said. First, the toilets would not take up space in a landfill. Second, using the waste product means less gravel is taken from the ground.

Twelve projects are pursuing Greenroads certification across the globe. Anthony said the city is working on future projects that will use recycled toilet materials and now residents can bring their toilets to the two local solid waste management facilities.

"So residents can save a few bucks in their trip to the dumpster," Anthony said.

He said the Greenroads certification guides planners and engineers through standard procedures so they can identify where to strengthen their sustainability efforts.

"Maybe it's a better design, construction practice, a better lighting standard - systematically it allows you to do things better," he said.