Sewage treatment plants may soon turn human waste into fuel, with the help of a new technology that mimics the conditions the Earth uses to create crude. The technology, hydrothermal liquefaction (HTL), creates a material similar to petroleum pumped out of the ground, with a small amount of water and oxygen mixed in.
Using HTL, organic matter can be broken down into simpler chemical compounds. The material is pressurized to 3,000 pounds per square inch – nearly one hundred times that of a car tire. Pressurised sludge then goes into a reactor system operating at about 350 degrees Celsius. The heat and pressure cause the cells of the waste material to break down into different fractions – biocrude and an aqueous liquid phase.
According to researchers from the US Department of Energy’s Pacific Northwest National Laboratory (PNNL), wastewater treatment plants treat about 34 billion gallons of sewage every day. That amount could produce the equivalent of up to about 30 million barrels of oil per year in the US. PNNL estimates that a single person could generate two to three gallons of biocrude per year.
Sewage, or more specifically sewage sludge, has long been viewed as a poor ingredient for producing biofuel because it is too wet. Conventionally, thermal drying is done, which is energy intensive and expensive. However, the new approach eliminates the need for drying.
HTL may also be used to make fuel from other types of wet organic feedstock, such as agricultural waste.