PNNL Produces Fuel from Sewage

Sewage, or more specifically sewage sludge, has long been viewed as a poor ingredient for producing biofuel because it's too wet. However, an approach being developed by the Pacific Northwest National Laboratory eliminates the need for drying required in current thermal technologies that convert wastewater to fuel.

The technology, called hydrothermal liquefaction (HTL), mimics the conditions the Earth uses to create crude oil, such as high pressure and temperature. The resulting material is similar to petroleum pumped out of the ground, with a small amount of water and oxygen mixed in. This biocrude can then be refined using conventional petroleum refining operations.

Using HTL, organic matter can be broken down to simpler chemical compounds. The organic matter is pressurized to 3,000 pounds/in². Pressurized sludge then goes into a reactor operating at about 660 °F. The heat and pressure cause the cells of the waste material to break down into biocrude.

Wastewater treatment plants in the U.S. treat approximately 34 billion gallons of sewage every day. That amount could produce approximately 30M barrels of oil per year.

HTL may also be used to make fuel from other types of wet organic feedstock, such as agricultural waste.