Unwanted oils and grease could heat buildings in Philly.
By Tom Avril
Philly.com green, August 2, 2010
Careful cooks know it's a smart idea to drain their cooking grease into a tin can for disposal, rather than letting it run down the drain.
Nevertheless, plenty of fats, oils, and grease end up at wastewater treatment plants, where they are typically skimmed off and taken to a landfill.
Now the Philadelphia Water Department plans to join the ranks of communities that have a more eco-friendly approach: turning the yucky scum into energy.
The plan is to convert the stuff into methane gas by putting it into a digester, essentially a big tank that contains anaerobic bacteria. The city already uses this process to break down wastewater sludge - generating methane that is burned to heat department facilities in the winter - but adding fats and grease into the mix requires some adjustment.
Metin Duran, an associate professor of engineering at Villanova University, says he is close to a solution, digesting the fats and grease in a five-gallon benchtop digester to determine just the right "recipe" for the full-scale operation.
"This stuff is really gross," admits Duran, who is working on the project with the national consulting firm of Brown & Caldwell. "You don't even want to look at it."
The variables in question include temperature and mixing rate, said Christopher S. Crockett, the Water Department's director of planning and research. The optimal recipe depends on the composition of Philadelphia's fats and grease.
"Not all scum is alike," Crockett says.
Sludge digestion, meanwhile, is done at two of the city's three treatment plants, and one of them also generates methane from another unwanted substance: aircraft deicing fluid.
During the summer, when buildings don't need heat, much of the resulting methane from the plants is burned off. But the plan is to build a cogeneration plant so that the gas also could generate electricity, Crockett says.
Sludge, and now fats and grease. Unpleasant? Not for bacteria, Duran says:
"The bugs just love this stuff."
Nevertheless, plenty of fats, oils, and grease end up at wastewater treatment plants, where they are typically skimmed off and taken to a landfill.
Now the Philadelphia Water Department plans to join the ranks of communities that have a more eco-friendly approach: turning the yucky scum into energy.
The plan is to convert the stuff into methane gas by putting it into a digester, essentially a big tank that contains anaerobic bacteria. The city already uses this process to break down wastewater sludge - generating methane that is burned to heat department facilities in the winter - but adding fats and grease into the mix requires some adjustment.
Metin Duran, an associate professor of engineering at Villanova University, says he is close to a solution, digesting the fats and grease in a five-gallon benchtop digester to determine just the right "recipe" for the full-scale operation.
"This stuff is really gross," admits Duran, who is working on the project with the national consulting firm of Brown & Caldwell. "You don't even want to look at it."
The variables in question include temperature and mixing rate, said Christopher S. Crockett, the Water Department's director of planning and research. The optimal recipe depends on the composition of Philadelphia's fats and grease.
"Not all scum is alike," Crockett says.
Sludge digestion, meanwhile, is done at two of the city's three treatment plants, and one of them also generates methane from another unwanted substance: aircraft deicing fluid.
During the summer, when buildings don't need heat, much of the resulting methane from the plants is burned off. But the plan is to build a cogeneration plant so that the gas also could generate electricity, Crockett says.
Sludge, and now fats and grease. Unpleasant? Not for bacteria, Duran says:
"The bugs just love this stuff."