Simple new process turns sewage sludge into "biocrude" oil

sewage to biocrude
© WE&RF

This "disruptive" new technology uses heat and pressure to convert sewage waste into an oil that has properties very similar to petroleum.

Using a technology called hydrothermal processing (HTP), researchers at the US Department of Energy's Pacific Northwest National Laboratory (PNNL) have produced a "biocrude" oil that can be further refined into liquid fuels similar to petroleum products, which calls for another round of singing "Oh, the wonderful things that poo can do."

"The best thing about this process is how simple it is. The reactor is literally a hot, pressurized tube. We've really accelerated hydrothermal conversion technology over the last six years to create a continuous, and scalable process which allows the use of wet wastes like sewage sludge." - Corinne Drennan, PNNL

The new process developed at PNNL has earned it the distinction of being called a "highly disruptive" technology in an evaluation by the Water Environment & Reuse Foundation (WERF), and the results of the bench-scale testing show that some 60% of the available carbon in the sewage sludge is converted into biocrude, with the other byproducts being a methane-rich gas (also a fuel) and water. This technology, when scaled up, has the potential to turn municipal wastewater treatment plants into renewable energy producers, while "virtually eliminating" the need for the processing, transport, and disposal of residuals from sewage treatment.

"HTP converts organic material into biocrude oil, natural gas, or both, with potentially more than 99% conversion of organics. HTP uses the same processes which form fossil fuels, (heat, pressure, time, and water), but amplifies these conditions so the conversion occurs in a much shorter timeframe. This technology is specifically designed for wet feed stocks. The byproduct is clear, sterile water." - WERF

The HTP process pressurizes the sludge to about 3,000 pounds per square inch, and then feeds it into a reactor that operates at about 660 degrees Fahrenheit, where the heat and pressure breaks down the cells of the feedstock into the biocrude oil and "an aqueous liquid phase" which can then also be treated and used to create other fuels and chemical products.

By enabling the use of a wet feedstock, this HTP process could open a lot of new doors for cleaner liquid fuels from organic materials, including agricultural waste, that have previously been dismissed as being inappropriate for biofuel production due to the need to dry them before using, which rendered them both expensive and energy-intensive to convert into fuels. However, before you start imagining that someday you could fuel your vehicle just with your own waste, PNNL estimates that a single person "could generate" just 2 to 3 gallons of biocrude per year, which isn't very much, but which could add up to the equivalent of some 30 million barrels of oil each year if all wastewater treatment plants in the US used the HTP process.

PNNL has licensed the new technology to Genifuel Corporation, based in Utah, which is working toward the creation of a demonstration plant with Metro Vancouver that could be operating as soon as 2018. And for those interested in a lifecycle analysis of the HTP process, PNNL has you covered right here.

Tags: Biofuels | Waste

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