Backyard Composting Evaluated in New York City
Diversion data following distribution of bins indicate that home composting probably won’t make a significant dent in New York City’s waste stream, but can more than pay its way and boost recycling awareness.
New York City may not normally be associated with yards and gardens, but there are good reasons to study backyard composting’s effect on waste diversion, especially because the impending closure of the city’s last landfill in 2001 means that nearly 12,000 tons/day of residential waste will have to be exported. The New York City “1996 Fresh Kills Landfill Closure Task Force Report” explicitly recommended studying backyard composting as an option for reducing waste going to export. Acting on this input, the city’s Department of Sanitation (DOS) designed and carried out a comprehensive evaluation of the diversion potential, participation rate, and cost-effectiveness of a residential backyard composting program, and published the results in August in its report, “Backyard Composting in New York City: A Comprehensive Program Evaluation.” The overall conclusion was that backyard composting will not have any measurable effect on diversion in New York City, but is a good way of promoting waste awareness among residents.
The study targeted four residential neighborhoods, one each in Brooklyn, the Bronx, Queens and Staten Island. (Manhattan, with its predominance of apartment buildings, was left out.) The areas chosen were suburban-style neighborhoods, complete with freestanding one or two family homes, tree lined streets, and blooming backyards. A baseline assessment was conducted in July, 1997 for a sample of 116 randomly selected households with backyards. It found they were generating an average of 45.6 lbs/household/week of trash and 16.3 lbs/household/week of recyclables for a diversion rate of 26.3 percent.
After the baseline assessment, residents with backyard access were contacted by employees of each borough’s Botanical Garden (working under contract for the DOS) and asked if they would like to volunteer for a community backyard composting program. Each program volunteer would qualify for home delivery and installation of an Earth Machine or Garden Gourmet compost bin, a scrap bucket, composting literature, and follow-up training and support all for $10.
This offer initially was made in a letter from each Botanical Garden, and was followed up by telephone solicitation and door-to-door canvassing. The entire program averaged about 500 staff hours/heighborhood and was designed to be as thorough as possible without annoying residents. The department’s goal was to obtain maximum participation, so that the full effects of backyard composting could be estimated realistically.
Leaves were used as a carbon source, but pilot participants were asked to compost primarily food residuals, since they comprise about 15 percent of New York City’s residential waste stream, compared to five percent for yard trimmings. Typical city backyards are too small to compost all yard trimmings generated, and a DOS program that collects large volumes of fall leaves and yard trimmings from Staten Island was in the process of expanding to other low-density neighborhoods throughout the city. Other DOS programs include grasscycling promotion and drop-off sites.
Residents who joined the backyard composting program were encouraged to begin right away, but were not informed of the second aspect of DOS’ research, which involved a waste composition study. Once before and twice after the volunteer recruitment period in July, curbside waste was collected from a random sample of residents in each neighborhood and analyzed for its composition of food residuals, yard trimmings, recyclables and other materials. The random sample included volunteering households, as well as residents who had declined to join the program and buy a bin. In addition, samples were collected from comparable households in a fifth neighborhood in Queens in which no composting program had been promoted. The purpose was to control for nonprogrammatic factors that might be affecting waste composition citywide, such as the weather.
These waste composition analyses were complemented by a telephone survey and focus group research of program volunteers and nonvolunteers. They were conducted to learn more about their reasons for deciding or declining to backyard compost, and their attitudes about recycling, waste management, the environment and the outdoors.
ASSESSING THE IMPACT
Many localities use surveys to learn about who is actually composting, but they generally rely on residents’ own estimates of how much they put into the bin. Some cities, like Seattle, have analyzed composition of waste on its way to the landfill, comparing citywide yard trimmings and food residuals composition before and after backyard programs have been implemented. New York City’s study, however, is the first to directly measure changes in waste composition at the household level, and also the first to use comparison groups of noncomposting households to rule out other factors that may be affecting waste composition.
“Some cities use surveys or standard composting rates to estimate diversion potential from backyard composting,” says Robert Lange, director of the department’s Bureau of Waste Prevention, Reuse and Recycling, who was in charge of the overall program design and evaluation. “That’s fine for smaller localities where there is a lot of space and yard material to compost.
But in New York, we have a unique situation. Our city is, for the most part, much more densely populated, and New York’s pace, in terms of work and enjoying time at home, is different from other areas of the country. With our massive waste stream, we felt it was especially important to take a realistic look at how much diversion we could expect from New York style backyard composting, and we feel very confident about the results we’ve achieved.”
The first major result was that despite DOS’ intense outreach, only 9.4 percent of households with backyards elected to join the composting program. This turnout was less than the department had expected, but market research among residents clarified why such a small proportion had shown interest it all came down to gardening. Avid gardeners, who could use the compost and already had an inclination towards working in their yards, easily saw the benefits to composting. Those without a green thumb, on the other hand, just couldn’t imagine composting if it was not a direct benefit to them (and this included people with an environmental bent).
Although there is no published data about backyard access in the city of New York, DOS market research estimates that as much as one-third of the 2.8 million households or around 930,000 homes have an outdoor area where they could place a bin. If 9.4 percent of them volunteered to compost, as many as 87,000 households throughout New York could take part. Of course, with a citywide program, outreach would have to be simplified, so 9.4 percent participation is an optimistic estimate. Still, it was one the department preferred to stick with, because it was based on actual experience.
WASTE COMPOSITION CHANGES, DIVERSION POTENTIAL
The waste composition study provided direct data about just how much the volunteers were composting each week. After controlling for extraneous factors, DOS found that composting households generated 2.5 pounds/household/week less in food residuals than noncomposting homes. Measurements of yard trimmings, on the other hand, fluctuated so greatly from household to household that it was impossible to assess the composting rate accurately.
An additional finding was that during the study period, while program participants threw out 1.5 lbs/week fewer recyclables in the trash, recycling increased among everyone in the test neighborhood by around 3.5 pounds/week, possibly due to the combined effect of program outreach and the visibility of DOS personnel during sample waste collection activities. The high-profile neighborhood presence, however, had more to do with the study than promoting composting itself, and would not be repeated if a backyard program were instituted citywide. This meant that the recycling boost couldn’t be relied upon in future programs, but the finding did suggest that attention to waste issues stimulated residents to recycle more.
Directly measuring the participation rate enabled the department to extrapolate the diversion potential of backyard composting for the entire city. Multiplying 87,000 composting homes by 2.5 lbs/week yielded an annual diversion of around 5,700 tons/year, or .15 percent of the 3.7 million tons of waste that New York City generates annually. Yard trimmings composting, were it able to be measured accurately, might raise the composting rate to something in the range of 5 lbs, but this would only increase the diversion from .15 percent to .30 percent. Clearly, backyard composting could not be relied on to make a dent in the export load of this metropolis.
COST EFFECTIVENESS AND EDUCATIONAL VALUE
The tiny diversion potential didn’t mean, however, that supporting backyard composting programs couldn’t be cost-effective. When the price of waste export was weighed against the costs of a slightly simplified compost bin distribution program, the numbers came out in favor of sending food residuals and yard trimmings back to the earth. In fact, when bins are distributed in one-day events requiring fewer staff hours, the cost to divert one ton of waste by composting is only $24, as compared to the roughly $100/ton that it would cost to export it by barge, truck or rail.
The department’s market research, furthermore, found that nearly everyone who volunteered in the compost program found it fun, rewarding, and well-run, a testimony to the expertise of New York City’s Botanical Gardens. In March, 1998, eight months after receiving their backyard bin, 92 percent of project participants reported that they were still composting. Over 70 percent said they would definitely recommend the program to family and friends, while 24 percent said they “probably” would do so. Focus group discussions revealed that the program got composters to think more about their waste in general, an effect that the department values as it continues to educate the public about waste prevention, reuse and recycling. So while backyard composting won’t solve New York’s waste export problems, it’s clearly something that DOS is committed to promoting in years to come.
This article was adapted from “Backyard Composting In New York City, A Comprehensive Program Evaluation,” a June, 1999 report prepared by the New York City Department of Sanitation.