Sludge-to-power process tested
If a University of Nevada, Reno, research project works as planned, municipal wastewater treatment facilities could turn their sludge into power for their own operations.
Researchers are demonstrating their sludge-drying equipment at the Truckee Meadows Water Reclamation Facility and ultimately hope to gasify the dry sludge product to power the plant. The system currently takes 20 pounds of sludge per hour and produces about 3 pounds of dried powder, but would need to be about 100 times that size to be commercially attractive to the industry, according to Chuck Coronella, principle investigator for the project and associate professor of chemical engineering at the school.
The sludge, about 75 to 80 percent water, is fed into a fluidized bed of sand and salts operating at about 165 degrees Fahrenheit, Coronella explained. As the sludge falls into the bed, it is heated to cause quick fragmentation. As it dries and fragments, the individual pieces become small and light and after some time, the particles of dried sludge are so light they are entrained with the fluidized air and carried out of the bed, he continued. The particles are then captured and stored for future use. “The principle advantage of this process is that it does not require high temperature heat,” Coronella said. “Our demonstration works with heat provided by water at 220 degrees Fahrenheit. Thus this is well-suited for a cogen configuration, with heat capture used for drying sludge. No external fuel will be required.”
After drying, the sludge is a low-moisture biomass fuel with a Btu value similar to that of dried wood, roughly 9,000 Btu per pound, according to Coronella. Researchers haven’t yet gasified the dried sludge product, but several configurations will be evaluated. Estimates show that the full-scale system could potentially generate 25,000 kilowatt-hours (kWh) per day, according to the university. Approximately 700,000 metric tons (771,000 tons) of dried sludge are produced annually in California municipalities, which would sustainably generate as many as 10 million kWh per day.
The collaboration with Truckee Meadows has been useful and the managers there are supportive, Coronella said. “They are enthusiastic about seeing the technology succeed. We have discussed with the TMWRF management about the possibility of doing a much larger demonstration on site, but we have not yet reached any conclusions.”
The demonstration-scale project is a collaboration with the cities of Reno and Sparks, operators of the wastewater treatment plant. The project is funded through the California Energy Innovations Small Grant Program, the California Energy Commission and the U.S. DOE, according to the university. The demonstration phase of the project was also chosen for funding by the university’s Tech Transfer Office under a DOE grant to support transferring technologies from the lab to practical application.