New method turns sewage sludge into renewable natural gas ^{CEFR B1}

A pilot study published in the Chemical Engineering Journal tested a new pretreatment method for sewage sludge collected from a nearby wastewater facility. The researchers pretreated the sludge before standard anaerobic digestion and reported 200% more renewable natural gas than current practices. The pretreatment also reduced final disposal cost by nearly 50% and can convert up to 80% of the sewage sludge into something valuable.

The study explains why the change matters. Wastewater treatment facilities use between 3% and 4% of total electricity demand in the US and add about 21 million metric tons of greenhouse gases each year. About half of the approximately 15,000 wastewater treatment plants in the US use anaerobic digestion, but that process is inefficient and leaves complex molecules in the sludge.

The new pretreatment exposes sludge to high temperature and pressure with a small amount of oxygen added before digestion. That oxygen under high pressure helps break long polymer chains. After pretreatment, the team used a novel bacterial strain to convert carbon dioxide with hydrogen into methane, producing renewable natural gas measured as 99% pure methane. The researchers say the method could both lower costs and provide a useful fuel.