Biofuels are often touted as an alternative to fossil fuels, but many depend on raw materials that would quickly become scarce if production were scaled up. As an alternative to these alternatives, the US Department of Energy’s Pacific Northwest National Laboratory (PNNL) has found a way to potentially produce 30 million barrels of biocrude oil per year from the 34 billion gal (128 billion liters) of raw sewage that Americans create every day.
According to PNNL, the problem with using sewage as a source material for biocrude is it’s too wet and requires drying before more conventional processes can handle it. PNNL’s approach is to use HydroThermal Liquefaction (HTL) to turn the sewage into oil, which removes the need for drying.
In HTL, the raw sewage is placed in a reactor that’s basically a tube pressurized to 3,000 lb/in2 (204 atm) and heated to 660° F (349° C), which mimics the same geological process that turned prehistoric organic matter into crude oil by breaking it down into simple compounds, only with HTL it takes minutes instead of epochs.
“There is plenty of carbon in municipal waste water sludge and interestingly, there are also fats,” says Corinne Drennan, who is responsible for bioenergy technologies research at PNNL. “The fats or lipids appear to facilitate the conversion of other materials in the waste water such as toilet paper, keep the sludge moving through the reactor, and produce a very high quality biocrude that, when refined, yields fuels such as gasoline, diesel and jet fuels.”