Researchers have developed a way to turn sewage into biocrude oil, using a process known as hydrothermal liquefaction to produce a material similar to the petroleum pumped from the ground.
With roughly 34 billion gallons of sewage treated in the US every day, the researchers say this system could create up to 30 million barrels of oil each year.
Scientists at the Department of Energy’s Pacific Northwest National Laboratory say the technology mimics the processes that naturally produce crude oil over millions of years.
But, it does so at high temperature and pressure, allowing for much faster output.
According to the researchers, the resulting biocrude oil can then be refined with conventional petroleum refining operations.
And, they say future systems using the technology could make for sustainable wastewater operations, with zero net energy, zero odours, and zero residuals.
While it’s long been thought that sewage sludge is too wet to generate biofuel, the approach used by the researchers at PNNL solves many of the previous problems.
It eliminates the need for drying, which has been known to make such conversions energy intensive and expensive.
With hydrothermal liquefaction, human waste or even other types of wet organic products, like agricultural waste, could be broken down into simpler chemical compounds, they say.
The researchers estimate that just one person could create two to three gallons of biocrude oil in a year.
To create the material, the waste is pressurized to 3,000 pounds per square inch, and subsequently fed into a reactor system that’s heated to roughly 660 degrees Fahrenheit.
The combination of these extreme conditions causes the cells of the waste material to break down into biocrude oil and an aqueous liquid phase.
And, the biodrude oil isn’t the only useful product.
The liquid phase could be treated with a catalyst to create other fuels and chemical products, the researchers say.
Along with this, the process also generates a small amount of solid material, which contains important nutrients including phosphorous, which could help to replace the phosphorous ore used in fertilizer production.
‘There is plenty of carbon in municipal waste water sludge and interestingly, there are also fats,’ said 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 wastewater 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.’
The researchers say that this process could also help local governments save money by eliminating the need for sewage residuals processing, transport, and disposal.
‘The best thing about this process is how simple it is,’ Drennan said. ‘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.’
In an independent examination for the Water Envionmental & Reuse Foundation, the process has been hailed a potential option for treating wastewater solids, and the investigators have even said it has high carbon conversion efficiency with nearly 60 percent of the available carbon becoming bio-crude.
The technology has now been licensed to Utah-based Genifuel Corporation, and is working with Metro Vancouver – including 23 local authorities in British Columbia, Canada – to build a demonstration plant.
Officials say the pilot project will cost between $8 and $9 million, and they have plans to see a start-up occur in 2018.
According to Darrell Mussatto, chair of Metro Vancouver’s Utilities Committee, ‘If this emerging technology is a success, a future production facility could lead the way for Metro Vancouver’s wastewater operation to meet its sustainability objectives of zero net energy, zero odours, and zero residuals.’
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