RICHLAND, Wash. – A professor with the Bioproducts, Sciences and Engineering Laboratory at Washington State University Tri-Cities is developing a way to drastically improve energy production at small waste water treatment plants. The research has the potential to be scaled globally.

Birgitte Ahring, professor of biological systems engineering and chemical engineering, received a $2.5 million grant from the U.S. Department of Energy Office of Energy Efficiency and Renewable Energy for the project. She is partnering locally with the Walla Walla Wastewater Treatment Plant, the Pacific Northwest National Laboratory and Clean-Vantage, LLC.

Sewage sludge is a remnant semi-solid material produced at sewage treatment plants. Ahring said while a portion of sludge is converted into biogas, at a mixture of 60% methane and 40% carbon dioxide at the majority of wastewater treatment facilities in the U.S., there still remains a significant portion of the waste to be disposed.

Ahring said converting a larger fraction of sewage sludge into useful energy will reduce the need for landfilling of the material and reduce the carbon footprint of wastewater treatment plants, worldwide.

New, more effective process

Ahring said many waste water treatment plants currently use a process called anaerobic digestion, which uses microorganisms that don’t require oxygen, to essentially digest some of the sludge material and to convert the organic material into biogas. Due to the nature of sewage sludge, part of the organic material will, however, be resistant to digestion using the process.

Ahring said a much higher amount of biogas can be produced by applying a specialized upfront pretreatment process using heat and oxygen-based agents before the anaerobic digestion process. In a final process step, she said the biogas can be further upgraded to pure methane, which can be used as a bio-natural gas. Methane gas can be used by an assortment of transportation industries, and thereby as a substitution for diesel and gasoline as a renewable fuel.

Together, the integrated new process has been named the “Advanced Pretreatment/Anaerobic digestion technology.”

“Many of these plants, like the one in Walla Walla, produce biogas by anaerobic digestion, but the low efficiency means that the amount of biogas is too low for organized use of this fraction,” Ahring said. “What DOE was calling for was a rethinking of the way we process sewage sludge today, so that the process becomes far more efficient and economically viable.”

Currently, 40 to 50% of the carbon in sewage sludge is converted in the biogas process, Ahring said. With the new process, the team estimates they can improve carbon conversion efficiency by more than 50% from the current level. With the biogas upgrading, the overall methane yield is expected to increase by more than 100% compared to what is currently produced at wastewater treatment plants.

Upscaling the project for use globally

Ahring said once the new process has been demonstrated in pilot scale through a BSEL-based pilot facility, the process will be ready for upscaling at small plants, such as the Walla Walla Wastewater Treatment Plant. From there, the process will be ready to disseminate broadly in the U.S. and even globally, she said.

Ahring said partner Clean-Vantage, LLC, has worked on the specialized pretreatment for years, and has successfully licensed the process overseas for other applications. With the new technique for upgrading the biogas to pure methane being developed at WSU, the overall concept will enhance the potential for sewage sludge as a raw material for renewable energy production.

Ahring is working with colleagues at PNNL to produce the technical economics for upscaling and a disposal cost model, which will detail the actual cost of the project at wastewater treatment plants based on size. The model will also detail how many extra dollars will be profited with the additional energy production at wastewater treatment plants.

“With this project, we can show we can produce a high-value product while reducing the amount of sludge needing final disposal,” she said. “We are getting rid of a waste problem and turning it into a useable product. Other cities can then take this model and implement it in their own areas. I am confident we will make it work. All of us involved on the project have a lot of expertise in this area, and we have previous experience in working together.”

Media contacts:

• Birgitte Ahring, ���سԹ� professor of biological systems engineering and chemical engineering, 509-372-7682, bka@wsu.edu
• Maegan Murray, ���سԹ� director of marketing and communication, 619-403-3617 (cell), maegan_murray@wsu.edu

By Maegan Murray, ���سԹ�

RICHLAND, Wash. – A method of converting a biofuel waste product into a usable and valuable commodity has been discovered by researchers at Washington State University and Pacific Northwest National Laboratory.

Converting algae to biofuels is a two-step process. The first, developed by , 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.

Bionatural gas 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 ���سԹ�’ Bioproducts, Sciences and Engineering Laboratory. But Ahring and her team have found that adapting anaerobic microbes — microbes that live without oxygen — to break down the remaining residue is a viable option. Through this process, the material becomes degradable and gets transformed into a bionatural gas 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 . 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
• 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,” Ahring said. “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.”

The ability to convert a waste product into a usable commodity provides algal biorefineries with a solution to a large problem, Ahring said.

“After removing the solids, about 10 percent of the output is bio oil, with the remaining 90 percent being a waste byproduct,” Schmidt said. “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.”

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,” Ahring said. “Creating a process to produce biofuels, bio-natural gas, 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.”

Schmidt said PNNL’s partnership with WSU allowed each team to focus on different aspects of the biomass conversion.  The collaboration is further enhanced by the Bioproducts, Sciences and Engineering Laboratory, a facility PNNL and WSU built together on the ���سԹ� campus nearly a decade ago.

“PNNL and WSU researchers interacted frequently on the project,” said Schmidt.   “While PNNL engineers focused on converting the algae to bio oil, the WSU team was able to delve deeply into fundamental research of wastewater conversion with microbes, which included taking advantage of unique analytical capabilities on the PNNL campus.”

A WSU alumnus himself, receiving both his bachelor’s and master’s degrees from WSU, Schmidt said he’s excited to team on additional programs and projects aligned with goals to grow the collaboration between PNNL and WSU.

 

Contacts:

• Birgitte Ahring, WSU Bioproducts, Sciences and Engineering Laboratory, 509-372-7682, bka@tricity.wsu.edu
• Maegan Murray, ���سԹ� marketing and communication, 509-372-7333, Maegan.murray@tricity.wsu.edu