Workmen stand behind a construction vehicle smoothing asphalt on a road
Turns out that, mixed with other ingredients, the cellulose from toilet paper looks and feels pretty much just like regular asphalt. KNN Cellulose

A parking lot and stretch of highway made from recycled toilet paper help move a portion of the sludge out of the wastewater stream.

Maintaining cycling infrastructure is a matter of course in the Netherlands, a country boasting 35,000 kilometers of bicycle paths. Still, the Dutch province of Friesland managed to make waves when it re-paved a bicycle highway last fall.

A 1-kilometer stretch of the bike roadway connecting the Frisian capital of Leeuwarden to the town of Stiens has the distinction of being the world’s first bicycle lane paved with toilet paper. Recycled toilet paper, that is.

Most roads in the Netherlands are paved with a blacktop called open-graded asphalt friction course (OGFC), which is porous and water permeable. Compared to more run-of-the-mill types of asphalt, OGFC requires higher volumes of bitumen, which binds together the stones and sand that make up the asphalt. Cellulose is added to thicken the mixture and prevent the bitumen from dripping off the aggregate during processing, transportation, and paving.

“When roads get wet, [they get] slippery, so we use this asphalt because it takes water away from the road surface quicker,” says Ernst Worrell, professor of energy, resources, and technological change at Utrecht University. Wicking water from the road is an important safety measure for a country that sees 27 to 35 inches of rainfall per year.

Meanwhile, the Dutch flush an estimated 180,000 tons of toilet paper annually. That paper makes its way to wastewater treatment plants, where it’s filtered out with the rest of the solids. The resulting sludge is dried and incinerated.

Aside from producing large amounts of CO2, the incineration process destroys many valuable resources found in wastewater, one of which is cellulose.

The bicycle path uses what’s called tertiary cellulose, extracted from waste streams, says Erik Pijlman, director at KNN Cellulose, one of the partners on the project. “We take the cellulose out of these streams and once again make it into a [raw material],” he says.

To do this, the paper fibers are sifted out of the wastewater by a 0.35 millimeter industrial sieve before proceeding through a series of machines to be cleaned, sterilized, bleached, and dried. The result is a fluffy, grayish material.

“If you look at it, you would not expect it to have originated from wastewater,” says Chris Reijken, wastewater treatment advisor at Waternet, one of 22 water authorities in the Netherlands, and part of the working group overseeing the project. “You can touch it, you can use it, it’s no problem.”

Toilet paper is made from either wood chips or recycled paper, so the quality of the fibers is high. What’s more, the uses for reclaimed cellulose are endless: asphalt mixes, pulp and paper, filters, building insulation, biofuel, textiles—anything that relies on cellulose from conventional sources. Because cellulose from wastewater has been in contact with human excrement, however, it cannot legally be used in products that would come into direct contact with people.

“Technically it could be used to make pizza boxes, but do you want your pizza wrapped in cellulose from wastewater?” asks Carlijn Lahaye, managing director at CirTec, the company that, together with KNN Cellulose, developed the technology for extracting and cleaning the cellulose fibers. With asphalt, any lingering pathogens are unlikely to survive the extreme temperatures of the asphalt mixing process.

It’s been more than a year since the toilet paper asphalt was laid in Friesland. To say it’s holding up well would be an understatement: It’s impossible to distinguish between this portion and the rest of the path. This past May, the same mixture was was used to reinforce a dyke on the West Frisian Island of Ameland and, in June, to repave the parking lot of a children’s petting zoo in Groningen. The city of Amsterdam has also expressed interest in using cellulose from wastewater in its roadways.

Dealing with the current sludge is costly for the water authorities, who easily pay 180 euros a ton to transport it to the incinerator, according to Yede van der Kooij of Wetterskip Fryslan, manager of the toilet paper-to-asphalt project. Those costs could be brought down by handing a portion of the sludge off to groups like KNN Cellulose and CirTec.

A sign on the Friesland bike path reminds cyclists that they’re riding over recycled toilet paper. (KNN Cellulose)

Reijken explains that it’s not easy to quantify precisely how much money this process could save. But LaHaye points to other benefits from sifting out solid waste materials that cause problems for pumps and mixers at the wastewater treatment plant. “The cellulose in the process is actually a burden in many cases, so if you take it out, you free up space, you use less energy in your process, you use less chemicals, you have less maintenance,” LaHaye says.

The downside? There might not be a way to repurpose all of it. Cellulose accounts for just 5 percent of the asphalt mixture. “To repair every single roadway in the Netherlands, we’d only need about 15,000 tons of fiber,” Van der Kooij says. Meanwhile, tertiary cellulose (from other waste sources, such as diapers and beverage cartons, in addition to toilet paper) has the potential to provide the country with one to two million tons per year.

In June, CirTec launched a plant in Geestmerambacht, to the north of Amsterdam. There, it’s experimenting with other regulation-compliant uses for cellulose, like bioplastics and biocomposites. The company is also exporting to the U.K., where researchers are looking at cellulose as an energy source and for use in other products.

“What we did is not only create technology and prove that it works, but we also have a market that is willing to take in the material,” Pijlman says. “And that’s really the next step in this kind of development.”

“It’s a strange idea for people that there’s [toilet paper] in the road,” says Michiel Schrier, provincial governor of Friesland. “But when they cycle on it or feel it, they can see that it’s normal asphalt.” It’s still too early to say whether products from recycled toilet paper will become mainstream, but, in the Netherlands, at least, they’re off to a good start.

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