Biofuel from Sewage

These days, more and more companies are finding that sewage is a veritable “black gold.” In recent years, sewage sludge has been mined for electricity, fertilizer, fish food, and gasoline. Now two companies have partnered up to turn sewage into ethanol. While others have worked to produce ethanol from municipal solid waste, sewage from wastewater has been a relatively unmined ethanol source.

The cellulosic ethanol company Qteros, in Marlborough, MA, and Applied Cleantech (ACT), a recycling company based in Israel, are combining technologies to turn sewage into ethanol biofuel. According to the companies, the process could produce high-quality biofuel while cutting down on monthly bills at wastewater treatment plants.

Jeff Hausthor, Qteros cofounder and senior project manager, says the recycling process uses solids from wastewater treatment as its primary feedstock - a material that facilities usually pay to have trucked away to landfills or used as fertilizer. “Given the feedstock has a negative cost, it is going to save every municipality money while they’re generating energy from something they needed to throw out before,” says Hausthor.

Sewage makes sense not just from an economic standpoint but also from a scientific one, according to Jim McMillan, a principal biochemical engineer at the National Renewable Energy Laboratory who is not involved in the project. One of the major steps in cellulosic ethanol production involves breaking down plant matter and separating cellulose from its tough lignin shell, either by mechanically shearing the material or by treating it with harsh chemicals. In contrast, the sewage that streams in from sewer pipes contains plant matter that is high in cellulose and low in lignin.

Six years ago, researchers at Applied Cleantech recognized sewage as an alternative cellulose source and designed a system to recover cellulose from wastewater treatment plants. As incoming sewage flows through the system, a series of mesh trays filters out liquid and recovers solids. Suspension tanks filter out sand from sludge, and the leftover mix is dried and pressed into pellets or pulp.

For the past year, Qteros has been feeding the mix to its ethanol-producing organism, the Q microbe, a bacterium that naturally eats plant material and ferments cellulose into ethanol using its own enzymes. Researchers found that the Q microbe produced 120 to 135 gallons of ethanol per ton of waste mix, compared with 100 gallons of ethanol per ton of conventional feedstocks like corn stover.

“We’ve reached a point where we know the Q likes the Recyllose,” says Hausthor. “We know how to pretreat the material and get it ready for the Q to eat, fork and knife, and we’re comfortable where we are on the technical side.”

NREL’s McMillan says the group’s results are encouraging, but he cautions that in an actual wastewater treatment plant, sewage may harbor organisms similar to the Q microbe that may be eager to compete for cellulose. “Sewage is dirty stuff, laden with all kinds of microbial activity,” says McMillan. “There might be a big biological background that might compete with the Q microbe, and everyone could join the party, the sugar-fest, making a lot of stuff you didn’t want to make.”

The companies plan to license the technology to wastewater treatment plants and municipalities. Qteros also just announced a location for a new $3.2 million pilot plant in western Massachusetts where the company will explore ways to pretreat feedstocks to get them ready for the Q microbe to convert into ethanol. Eventually, Qteros plans to build a plant with an integrated biorefinery where the company will introduce the Q microbe to a number of feedstocks to produce ethanol at a larger scale.

The biofuels company Mascoma is also using microorganisms to turn waste into cellulosic ethanol. Justin van Rooyen, director of business development at Mascoma, says the partnership between sewage and ethanol is a promising one.

“At first glance it seems strange, but it makes sense,” says van Rooyen. “There are a lot of assets to a wastewater treatment facility. There is already waste disposal on site, and the feedstock is collected in one place. It works as a great demonstration. Whether it will make good business remains to be seen.”