Instead, residents will be encouraged to pulverize their veggie trimmings, orange rinds, and leftovers in the disposal, sending it to the city’s treatment plants, where it will provide fuel for electricity generation and be transformed into fertilizer.
“We’re excited about this project because it allows us to continue to decrease the amount of waste that gets wasted,” said Streets Commissioner Clarena I.W. Tolson.
The city is partnering with a major manufacturer, InSinkErator, which will provide and install the 200 disposals. The company also is offering $20 rebates to residents elsewhere in the city who install their “Evolution” devices, priced from $179 to $329.
Putting food waste into the sewer system means gravity instead of diesel-fueled trucks will get it to its destination. It will become a resource instead of refuse.
“This is another area where Philadelphia is ahead of the curve,” said Charles Haas, Drexel University’s Betz professor of environmental engineering.
In some corners, however, the devices are viewed as guzzling water, burning electricity, clogging pipes, and inundating already-stressed sewer systems.
The industry counters that newer devices use about a gallon and a half of water a day and cost less than 50 cents a year in electricity.
Others wonder whatever happened to composting.
Biosolids are not the same as compost. “They are not soil, and they are no longer part of the living cycle,” said composting advocate M. Lee Meinicke.
Meinicke is president of Philly Compost, an organics recycling company that with two other companies currently handles food waste from 400 homes. “If composting advocates had the same kind of money as InSinkErator,” she said, “could we have gotten them to do a similar program around composting?”
Tolson said the city has had a program to distribute composting bins. The disposals are simply another option.
The water department is eager to get more organic material. The sewer plant is already designed to treat the waste from your toilet, and the food from your dinner plate is pretty much the same thing, “from a chemical point of view,” said Christopher Crockett, the department’s deputy commissioner for environmental services.
And what happens downstream at the treatment plants is a lot like what happens in your stomach. There, the waste is put into an anaerobic digester, which even operates at near human temperatures, 94 to 98 degrees.
Inside, bacteria digest the material and emit gas — methane — which is burned to generate electricity. The water department is building a $47 million power plant at its Northeast facility that is projected to produce 85 percent of the facility’s power needs.
The leftover gunk winds up at the city’s biosolids plant near the airport, where it is dried and processed into pellets, to be sold as fertilizer for golf courses or farms and as fuel for concrete factories and lime kilns.
The InSinkErator project ties into the water department’s broader mission to transform its operation from waste treatment to resource recovery, Crockett said.
Although the city has a sewer system that overflows during heavy rains — and is implementing a $2 billion plan to deal with that — Crockett said the added water from garbage disposals would be minimal. A bigger concern, he said, is leaking toilets, which can drip the equivalent of 25 flushes a day.
InSinkErator officials said they never really thought about the green attributes of their devices until recently. Instead, they were pushing convenience.
But “in the last five years, the subject of food scraps has become, surprisingly, a hot subject,” said Dave MacNair, vice president of marketing with the company.
What InSinkErator gets from the deal is data and public exposure — the city has agreed to an education and advocacy campaign.
The homes getting the 200 free devices are on two trash routes of about 500 homes each. The city has baseline statistics on the current trash stream.
“We’ve examined it, weighed it, and determined how much is food,” said Tolson — 10 percent. Three months and six months from now, the city will do more analyses to quantify the effect of the added disposals.
Nationwide, some cities have banned the devices because greases and fats can cause problems at sewage treatment plants, said Leonard K. Bernstein, an engineer who is a member of the American Public Works Association.
In Philadelphia’s suburban areas, the water quality in streams is impaired and additional nutrients — like the phosphorus and nitrogen in food waste — must be managed, said a state Department of Environmental Protection spokeswoman. So, it becomes a matter of knowing your treatment plant and what it can manage.
Grease coagulating in aging pipes is a concern, too. In Cheltenham, for instance, the township recommends that residents minimize the use of garbage disposals to reduce the risk of sewer backups.
Contact Sandy Bauers at 215-854-5147, firstname.lastname@example.org, or follow on Twitter @sbauers. Read her blog, “GreenSpace,” at www.philly.com/greenspace