Wastewater treatment plants use about 3% to 4% of all electricity in the U.S., and most people wouldn’t turn to them for green energy. Additionally, scientists say these plants release millions of tons of greenhouse gases every year. Most plants try to break down waste using microbes. However, this process is slow, inefficient, and leaves behind a lot of sludge that ends up in a landfill.

Researchers at Washington State University have developed a method that turns 80% of leftover sewage sludge into renewable natural gas. Additionally, this new process could cut the cost of treating the waste by nearly half.

From Sewage to Renewable Power

The two-step process begins with treating the sludge with high pressure and heat, adding oxygen to help break down tough molecules. This makes it much easier for the system to digest the waste later on. After that, they bring in a special bacteria they discovered to clean up the gas produced.

The result is a renewable gas that is 99% pure methane.

“This technology basically converts up to 80% of the sewage sludge into something valuable,” said Birgitte Ahring, a professor at WSU. “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.”

Simple and Efficient

One of the most interesting things about the study is the bacteria the team used to upgrade the gas because it is extremely low-maintanence. “This bug doesn’t need anything — it is a workhorse,” Ahring said. “It doesn’t need organic additives or a lot of nursing. It does well with water and a vitamin pill.”

By combining this bacteria with their high-pressure pretreatment, the researchers dropped the cost of treating sewage from $494 per ton to just $253.

“This approach not only enhances carbon conversion efficiency and methane yield but also enables direct production of pipeline-quality renewable natural gas with minimal CO2 content — addressing two major limitations of existing sludge-to-energy systems into a single, scalable methodology,” Ahring explained. “By successfully bridging advanced pretreatment with biological biogas upgrading, this work provides a new, integrated paradigm for sustainable sludge treatment maximizing energy recovery while contributing to the circular bioeconomy.”