Washington State University has transformed sewage sludge’s environmental liability into a valuable energy asset. 

A successful pilot program has validated a dual-benefit method for wastewater management: it produces cleaner natural gas more efficiently and lowers the overall cost of waste disposal.

Interestingly, the local sewage sludge was pretreated, resulting in a 200 percent increase in renewable natural gas production while cutting disposal costs in half. 

This high-purity gas serves as a direct, climate-friendly replacement for fossil fuels, capable of heating homes, generating electricity, and powering transportation using existing infrastructure.

“This technology basically converts up to 80 percent of the sewage sludge into something valuable,” said Birgitte Ahring, a professor in WSU’s Bioproducts, Sciences, and Engineering Laboratory and the Gene and Linda Voiland School of Chemical Engineering and Bioengineering.

“If we can replicate this work on other organic materials, we’ll have a waste treatment technology that is world-class when it comes to efficiency,” the corresponding author added. 

High conversion rate

With roughly 15,000 facilities operating nationwide, wastewater treatment represents a massive and constant drain on the American power grid.

These plants are notorious energy hogs, consuming nearly 4 percent of the country’s total electricity to process municipal waste.

For many small communities, the local treatment plant is not just a utility but the single largest electricity user in the entire area.

In addition, the wastewater treatment emits 21 million metric tons of greenhouse gases every year. 

These plants are slow and messy as they use anaerobic digestion to manage waste. 

Microbes struggle to break down the tough, complex molecules found in human waste, leaving behind mountains of “biosolids” that usually end up in landfills.

The WSU team created a two-step punch. 

By integrating advanced pretreatment with a novel bacterial strain, the team has created a “circular bioeconomy” model that outperforms current wastewater treatment standards.

First, in the pretreatment step, the sludge was heated to high temperatures and exposed to oxygen. Under pressure, the oxygen acts like a chemical chainsaw, shredding long molecular chains into bite-sized pieces for bacteria.

After this, a newly discovered, patented bacterial strain was introduced. Unlike many industrial methods that rely on toxic chemicals or pricey catalysts, this bug is low-maintenance.

“This bug doesn’t need anything—it is a workhorse. It doesn’t need organic additives or a lot of nursing. It does well with water and a vitamin pill,” Ahring noted in the press release.

Reducing treatment cost

The bacterial strain converts carbon dioxide and hydrogen into 99 percent pure methane or renewable natural gas. This efficiency gain nearly halved the treatment cost, dropping it from $494 to $253 per ton. 

With a patent secured through WSU’s Office of Innovation and Entrepreneurship, the team is now partnering with industry to scale the technology for commercial use. 

Professor Ahring notes that the system maximizes methane yield while producing pipeline-ready gas. 

The project merges advanced pretreatment with biological upgrading to create a new, scalable model for the circular bioeconomy, transforming waste management into a high-efficiency energy recovery system.

If they succeed, the 21 million metric tons of greenhouse gases currently belched out by water treatment plants could become a thing of the past.

The findings were reported in the Chemical Engineering Journal.