Do garbage disposals help gum up Seattle sewers?
Water runs into the opening of a typical home food waste disposal mounted under in a kitchen sink.
Flick the switch and a kitchen garbage disposal will growl as it gulps down food scraps in your sink.
A convenience in nearly half of U.S. households, the garbage disposal churns food scraps into tiny particles that slip easily down the drain. But some wastewater officials say garbage disposals encourage people to flush down fatty foods that shouldn't go in the drain because they clog up the sewer system, causing overflows.
As part of an effort to keep the pipes unclogged, the city's sewer stewards are urging people to compost or recycle food scraps instead.
"It's what they're putting down garbage disposals. That's where the real problem is," said Julie Howell, Pollution Prevention Program Coordinator with Seattle Public Utilities."If they have disposals, they tend to be indiscriminate about what goes down it."
Defenders of the 80-year-old invention, also known as a food waste disposal, say grease concerns are overblown and refuted by independent research. If anything, some defenders argue, disposals help the environment by diverting food scraps from trash bins and landfills to wastewater treatment plants, where they can be converted for energy or fertilizer. That's important because food scraps are 10 to 20 percent of household waste, they say.
"There are a lot of myths and misconceptions about disposers. Food waste is 70 percent water -- about the same gravity as human waste. A treatment plant is capable of disposing of that material since it's essentially the same as human waste," said Michael Keleman, an environmental engineer with InSinkErator, the largest manufacturer of garbage disposers worldwide and based in Racine, Wis.
Last month, seattlepi.com reported on the coronary-like conditions in many of the city's sewer pipes caused by fats, oils and greases, or what utility workers call "FOG." It causes about 30 percent of the city's wastewater overflows and requires routine maintenance on problem spots. SPU estimates about 544,000 gallons of grease get into the sewers every month, enough to fill seven large swimming pools. The utility is studying the causes and taking steps to reduce it by working with restaurants around the greasiest sewer lines and educating residents not to dump grease down the drain.
Most of the grease is a byproduct of dishwashing from restaurants, but about 40 percent is traced back to residential neighborhoods, city officials say. Howell said people with garbage disposers tend to toss in meat scraps or poultry bones, and are more apt to scrape fatty leftovers into the drain because they think a garbage disposal will easily render the remnants safe for the sewer pipes.
But there are some who question whether you can blame an appliance for the bad habits of people who scrape the most problematic subtances -- gravy, creams, and sauces -- into the drain.
"We certainly encourage people not to put those materials down there. And certainly, education is a big part of promoting the use of disposers," Keleman said.
There also is concern about commercial-grade food waste grinders used by restaurants. Many restaurants are required to install grease traps, which act as a reservoir for grease that breaks free during dishwashing and keeps it from leaking into sewer pipes. But under the Uniform Plumbing Code, which Washington state adopts, restaurants can install food waste grinders directly to the sanitary sewer system, said Dave Cantrell, chief plumbing inspector for the Seattle-King County Public Health department.
"Just from a common sense point-of-view, food particles are going to have grease and if you're dumping them down the drain and bypassing food interceptors, you're letting the worst culprit go free," he said.
He said he's working with SPU to study Seattle's situation and whether regulatory changes should be pursued. Organizations that set the national plumbing codes are having the same debate about regulations on disposers in commercial establishments, he said.
Two other cities have experimented with banning garbage disposals because officials were concerned they exacerbated sewer clogs, although one of the bans was not specifically due to grease concerns. In both New York City and Raleigh, N.C., those bans were repealed.
Believe it or not, researchers have actually studied the nature of sewer grease in an effort to answer some of these questions.
A few years ago, a study by the Water Environment Research Foundation attempted to define the nature of sewer grease and find ways that cities could better prevent its formation. Samples from 30 cities were analyzed (Seattle was not a participant), allowing researchers to determine that most of the gunk was made up of calcified fats, formed through a chemical process similar to how soap is made.
But the samples didn't contain food particles, which suggested to some that grease isn't coming from garbage disposals.
"There was nothing visible where we could say these are scraps of muscle or chicken or beef. All I can say is that based on the scientific evidence we have, there is nothing to suggest (garbage disposals) are contributing directly," said Kevin Keener, an associate professor of food sciences at Purdue University who led the FOG portion of the research. "A meat scrap may be a substantial source for that fat, but it's not contributing directly."
Instead, the study identified household sanitizers, detergents and other cleaning agents as potentially more problematic because when they combine with grease, they trigger the chemical reaction that causes it to transform into a rock-hard substance.
For the last decade, the city of Raleigh, N.C., has had an ordinance restricting the disposal of anything but human waste, used water and toilet paper into the sanitary sewer system. That means no food scraps. Since the law took effect in 1999, the number of sewer overflows each year has dropped, from an average of 70 to 53. Last year marked the first time that FOG build-up wasn't the leading cause of sewer overflows, said Marti Gibson, environmental coordinator for wastewater in the city's public utilities department.
Part of the success is Raleigh's aggressive anti-FOG program and education campaign on keeping grease out of the sewers, she said. But she thinks the trend indicates a nexus between food scraps and grease.
Raleigh also attempted to outlaw garbage disposals in new construction in 2008. Only a month later, the City Council repealed the ban after intense pushback from residents and the garbage disposal industry, including representatives InSinkErator and General Electric, as well as national media attention. Company representatives cited Keener's research in their presentation to the City Council.
"But there is still an ordinance on the books that makes it illegal to dispose of anything other than human body waste or used toilet paper," she said. "So, how you can put them in your garbage disposal without having them go into the sanitary sewer system?"
Never pour oil of grease down the drain. Allow cooked fats, oil or grease to cool and pour them into a disposal container than can be tossed out with solid wastes.
Thoroughly scrape plates to remove leftover fat, oil, grease and food waste from pots, pans and cooking equipment prior to rinsing. Use paper towels, if needed, to wipe greasy dishes before dishwashing.
For more information on disposing and recycling grease, visit www.resourceventure.org. SPU also keeps this list of local companies that handle grease recycling and maintenance of pre-treatment devices.