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WSU, PNNL convert biofuel waste into commodity, now targeting sewage sludge

A method of converting an algal biofuel waste product into a usable and valuable commodity has been discovered by researchers at Washington State University (WSU) and Pacific Northwest National Laboratory (PNNL) in the United States (US).

WSU Professor Birgitte Ahring, centre, points to test sample, with her research team (photo courtesy WSU).

Converting algae to biofuels is a two-step process. The first, developed by PNNL, applies high pressure and high temperature to algae to create bio-oil. The second converts that bio-oil into biofuel, which can replace gasoline, diesel and jet fuel.

It’s that first step, called hydrothermal liquefaction, that produces waste — approximately 25 to 40 percent of carbon and 80 percent of nutrients from the algae are left behind in wastewater streams.

Biogas and fertilizer

The wastewater is generally hard to process because it contains a variety of different chemicals in small concentrations, said Birgitte K. Ahring, professor at WSU Tri-Cities’ Bioproducts, Sciences and Engineering Laboratory.

But Ahring and her team have found that adapting anaerobic microbes to break down the remaining residue is a viable option. Through this process, the material becomes degradable and gets transformed into a biogas without the use of harsh chemicals. The solid material that remains can also be applied as a fertilizer or recycled back into the hydrothermal liquefaction process for further use.

The results of the team’s research are published this month in Bioresource Technology. Called “Anaerobic digestion of organic fraction from hydrothermal liquefied algae wastewater byproduct”, the team also consists of Keerthi Srinivas, WSU postdoctoral research associate, Sebastian Fernandez, WSU research assistant, Andrew Schmidt, of PNNL’s chemical and biological processes development group and Marie Swita, of PNNL’s chemical and biological processes development group.

Don’t waste waste

It has always been my mantra that we shouldn’t waste waste. We had an idea that we could turn this waste product into something useful, such as a fertilizer. Our findings revealed that we could use this waste product as something much more, Ahring said.

Ahring points out that the ability to convert a waste product into a usable commodity provides algal biorefineries with a solution to a large problem.

After removing the solids, about 10 percent of the output is bio oil, with the remaining 90 percent being a waste byproduct. The fact that we’ve developed an alternative method to recycle or treat the leftover material means it’s more economical to produce the bio oil, making the potential for commercial use of the process more likely, saidAndrew Schmidt, of PNNL’s chemical and biological processes development group.

Sewage sludge and wastewater

Ahring said the team’s results were so promising that they are now partnering with PNNL on its conversion of sewage sludge to fuel using a similar strategy for the wastewater.

Today, sewage sludge is found throughout the world. Creating a process to produce biofuels, biogas, and nutrients from this material would be of major importance. The current study has demonstrated that nothing should ever be regarded as a waste, but instead as a resource, Ahring said.

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