How to turn wastewater sludge into vehicle fuel

Start with stinky sewer plant sludge, add some high-tech processes and miles of pipe, and out comes affordable, compressed natural gas vehicle fuel.

The city of Grand Junction is the first in Colorado to build a facility that processes methane gas released from the anaerobic digester portion of the municipal wastewater plant and converts that to CNG for use in fleet vehicles.

“Making lemonade out of lemons is nothing; try to make vehicle fuel out of sewage,” said Dan Tonello, Grand Junction wastewater services manager. “It’s the first of its size and type in the nation. Methane gas is a valuable resource that should not be wasted, and it makes good environmental and financial sense.”

Foresighted city council members and city employees started in 2006 working toward utilizing the excess methane that was being largely flared and wasted at the sewer plant. Only 16 percent of the methane was being used to heat digestion tanks.

“The open flare was burning for 31 years, and we produce about 120,000 cubic feet of methane a day. The remainder was being flared off at 100,000 cubic feet per day or the rough equivalent of 400 to 500 gallons of gasoline,” Tonello said.

Consulting engineers investigated three options to use the methane and determined that CNG for vehicles provided the best rate of return. The $2.8 million renewable CNG system opened this April. Currently the city fuels 51 vehicles on 20 slow-fill pumps and two fast-fill hoses for CNG that costs $1.04 per gasoline gallon equivalent to produce, noted Jay Valentine, Grand Junction internal services manager. The city’s CNG fleet ranges from trash trucks to pickups to Ford Transit Connect vans.

Other U.S. locations have biomethane plants at active trash dumps, yet Tonello said methane from a wastewater facility needs less purification and is an infinite resource. The Grand Junction plant serves a daytime population of more than 70,000 people and treats 8.1 million gallons of wastewater per day.

This fall the facility was certified to sell biofuel credits to help larger refineries or oil import companies meet federal Renewable Fuel Standards, Valentine explained, which adds significant revenue. Initial infrastructure investments in the biofuel system, supported by various grants, should be paid back in seven years.cb