Novel waste treatment could fuel rural communities

A Washington State University research team has developed a new method to treat sewage which can convert leftover sludge into biogas. The method could help wastewater treatment plants reduce waste while also generating electricity.

The research team tested a pretreatment technology using oxygen-containing, high-pressure steam that acts as a catalyst to break down sewage sludge. They found that they were able to convert more than 85% of the organic material to biogas, which can be used to produce electricity or upgraded to renewable natural gas (RNG) for the natural gas grid or for local use.

Adding the pretreatment step improved the anaerobic conversion of sewage sludge at the wastewater treatment facility from the current less-than-50% conversion rate, and they produced 98% more methane overall compared to current practice. 

“It was shown to be extremely efficient, and that’s very exciting,” said Birgitte Ahring, professor in the Gene and Linda Voiland School of Chemical Engineering and Bioengineering, who led the work. “This can be applicable and something we could begin to explore in Washington state. Not wasting waste but using its potential instead has major advantages.”

The WSU researchers have been studying this pretreatment process for several years, using it to break down straw and woody materials. They weren’t sure the process would work with the different composition of sewage sludge, such as lipids and proteins, but were positively surprised.

“This is not a very high-tech solution,” Ahring said. “It’s actually a solution that can be useful even at small scale. The efficiency has to be high or else you cannot warrant adding the extra costs to the process.”

The technology could be particularly helpful for smaller communities, many of which are motivated to reduce waste and their climate impact, she added.

The researchers are now scaling up the work in their pilot facility located at WSU Tri-cities to further demonstrate the process. They are also studying how to efficiently convert the biogas to more valuable renewable natural gas by a new bioprocess. While the biogas can be used to produce electricity, producing renewable natural gas could allow rural communities to produce local transportation fuel for fuelling their municipal vehicles.

The findings were reported in the journal Waste Management.

Image credit: iStock.com/Bilanol