By: Lakis Polycarpou, member of Tarrytown Environmental Advisory Council, FCWC member organization
A few weeks ago, the New York City Council passed a series of major new environmental regulations, including a provision that will require composting of food waste at large restaurants in the city. It’s a move that’s only the latest step in rapidly spreading change in how Americans deal with food waste.
According to the EPA, food scraps, yard waste and other organic materials account for more than 50 percent of the waste stream in the US, are the third largest source of methane emissions when landfilled, and are a potential source of dioxin and other toxic pollution when incinerated. In addition, as energy prices rise and overloaded landfills close, collecting and disposing of wastes presents a growing operational cost, as municipalities and businesses must ship trash greater and greater distances.
In the last few years, a growing number of municipalities have realized that separating organic materials at the source and composting them is a relatively simple step that can yield huge environmental benefits. In the last decade, the city of San Francisco pioneered municipal composting by requiring restaurants and businesses to separate organic materials for collection. In 2009, the program was expanded to residences, adding a third bin to collect compostable materials in addition to recyclables and trash.
San Francisco’s initiative has reduced the city’s carbon emissions to nearly 12 percent below 1990s levels. Similar programs in Seattle and Portland have had equally impressive results; Portland’s diversion program reduced landfill trash collection by almost 40 percent within a year of implementation. By some calculations, if every US city had similar collection programs, the nation could offset 20 percent of its overall carbon emissions.
While there are many approaches to composting food waste, most systems fall broadly into three categories: vermicomposting, aerobic and anaerobic composting. Check out our blog, for the details of these three types of composting.
Vermicomposting or worm composting, involves using certain species of earthworms (most commonly Red Wrigglers) to eat and digest wastes. Worm manure (castings) is a nutrient-rich, black humus that is used as a valuable fertilizer. Worm composting is frequently used in small-scale backyard systems (or even in the home). It has the advantage of relative simplicity, and unlike aerobic composting does not require large amounts of carbon-rich or “brown” materials like dried leaves to work. Disadvantages: worm composting doesn’t work for large amounts of meat or dairy waste, and is less practical outdoors in winter, where cold temperature freeze piles and can kill the worms.
Aerobic composting is the most common form of backyard composting, but can be scaled up to very large systems. Aerobic composting involves creating conditions that favor oxygen-loving bacteria which is usually accomplished turning the pile to aerate it. At the backyard scale, turning can be done with by hand, using a pitchfork or cranking an enclosed tumbler. At the larger municipal or farm scale, operators use mechanical equipment (such as front loader) to pile and turn long windrows to produce compost. Alternatively, pumps can be used to blow air into the pile.
Aerobic composting has many advantages. Because oxygen-loving bacteria both produce and thrive in high temperatures, a pile that has the right ratio of materials and is properly aerated will rapidly heat up to the point where all dangerous pathogens are killed, along with weed seeds. This allows well-managed systems to accept a broader range of wastes, including meat, dairy and oils.
One disadvantage of aerobic composting is that it requires a proper mix of “green” or nitrogen-rich materials (food scraps, manure, fresh grass) and “brown” or carbon-heavy materials (dried leaves, sawdust, woodchips, paper) for optimal results. If a pile has too many “greens” it may go anaerobic and produce noxious odors; if it has too many “browns” the composting process may slow down or stop.
Anaerobic composting happens in conditions where oxygen does not penetrate the pile, favoring the growth anaerobic bacteria. These bacteria ferment organic compounds, producing methane (natural gas). In nature anaerobic composting is happens in swamps and marshes, where deep layers of sediment decompose. It is also the dominant process in landfills, where thick piles of organic material produce large quantities of methane, a greenhouse gas that is many times more potent than carbon dioxide, as well as foul-smelling gases.
However, if the organic material is held in an enclosed container or “digester,” the methane or “biogas” can be captured and burned for energy as natural gas, with the remaining sludge left as fertilizer.
One disadvantage of biogas digestion is smell (though smells are limited if the system is properly designed). In addition, unlike aerobic composting, anaerobic systems do not heat up enough to rapidly kill pathogens; anaerobic sludge must sit for six months or longer before it is safe to use as fertilizer.
In Westchester County a number of groups are working on pilot projects to begin diverting and composting the county’s food waste and other organic materials. There is a currently a team of local organics waste specialists (Braeden Cohen, Lakis Polycarpou and Elisa Zazzera) working to site and implement an aerobic compost pilot project for food waste with the coordination and assistance of Anne-Jaffe Holmes of the Greenburgh Nature Center.
In addition, Thomas Culhane, a professor at Mercy College and expert on anerobic biogas digestion, is leading a team to build and showcase an anearobic biogas system in Westchester as well. The team recently put together a mold for a biogas digester that is currently on display at Hart’s Brook Nature Preserve in Hartsdale. From there the mold will travel to Ohio State University before returning to help build a demonstration biogas digestion system at the Greenburgh Nature Center.
Whichever system is used, diverting food waste from landfills or incinerators for composting makes sense. Because composting produces resources (energy and/or valuable fertilizers) and immediately reduces waste disposal costs, municipal composting projects can become revenue neutral or even profitable in a relatively short amount of time, making such projects one of the most cost-effective steps on the road to a more sustainable culture.