North Carolina State University researchers have developed what is, to date, the most efficient means of converting sewage sludge and restaurant grease into methane.
After treating sewage, wastewater treatment plants are left with solid sludge, called biosolids. For years, utilities have treated biosolids with microbes that produce methane. In recent years, utilities have been adding grease interceptor waste (GIW) into the mix.
Grease interceptors are used to trap fat, oil and grease from food service establishments so that they don’t clog up sewers. By adding GIW in with their biosolids, utilities can produce more methane, making the entire operation more efficient. But there are challenges.
“Turning biosolids and GIW into a renewable source of clean energy is a laudable goal,” says Francis de los Reyes, a professor of civil, construction and environmental engineering at NC State and lead author of a paper on the work. “But if you add too much GIW into the anaerobic digester they use to treat biosolids, the system goes haywire – and methane production plummets.
“Our goal with this work was to figure out the best balance of biosolids and GIW for maximizing methane production. And we were able to make significant advances.”
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