Biogas: the city’s new compost power

As the city considers alternative energy sources, biogas is a largely untapped possibility.

Compost bins in NYC. Source from www.facebook.com/GrandArmyPlazaGreenmarket

Compost bins in NYC. Source from www.facebook.com/GrandArmyPlazaGreenmarket

Biogas originates from decomposing manure, sewage, plant and food remnants. Ordinary compost, soon to be collected from kitchens and restaurants across the city, is a potential feedstock for biogas, if the necessary infrastructure is in place — and our forward-thinking mayor has included a biogas facility in his plans for New York City’s composting initiative.

Biogas is commonly known as ‘swamp gas’ or ‘landfill gas’ (LFG). It has been widely adopted as an alternative energy source to power vehicles, generate electricity, and provide heating in Germany, Sweden, and Switzerland.

Typically, the problem with allowing organic waste to decompose without controlling it is that it produces large quantities of methane, which is a greenhouse gas more than 20 times more potent than carbon dioxide. Big methane producers are landfills and livestock, as well as leaks from natural gas pipelines. (Cows are such a prominent source of methane, as they digest their feed, that research is underway to create new breeds that produce less gas.)

Biogas plants are a way to collect and use organically produced methane for heat or power, in the same way natural gas is typically utilized. The real benefit of biogas is that it is a carbon neutral energy source — as with any natural gas source, CO2 is emitted as biogas is burned, but in this case the it’s only as much as the organic material contained in the first place. The next round of plant material, or Chipotle left-overs, that forms the basis of the biogas supply had taken in new CO2 as it was grown, keeping the overall system in balance.

Biogas_plant_sketch_ENG

One leader in biogas use in NYC is the Freshkills landfill, which will become Freshkills Park. This vast underground landfill on Staten Island produces large quantities of methane. The Department of Sanitation harvests and sells the methane to the utility National Grid. Freshkills produces enough methane to power 22,000 homes a year and is a source of $12 million in annual revenue. Still, there is a far greater source of untapped biogas in the city.

Of all the garbage discarded by New Yorkers, nearly 30 percent is easily compostable on a local level. An extra twelve percent of waste could be composted on an industrial scale. Mayor Bloomberg is seeking to make composting widespread in NYC. A pilot program running in Staten Island was met with enough participation that it will expand to five percent of households in NYC next year. It seems that in a few years, separating compost will be mandatory for New Yorkers. This would reduce landfill volume greatly, as organic material represents thirty percent of city garbage. Not only would recycling this waste benefit the environment, it would save the city a chunk of the $336 million it annually spends on residential garbage disposal.

Image source from http://www.nyc.gov/html/nycwasteless/html/resources/wcs_organics.shtml

Image source from http://www.nyc.gov/html/nycwasteless/html/resources/wcs_organics.shtml

To harness the potential energy in compost, Bloomberg plans to hire a composting plant to convert up to 100,000 tons of compost a year into biogas and usable soil. If Bloomberg’s initiative is maintained by his successor, composting will become a rule for all city residents. City Atlas is looking into how much compost it would take to power a neighborhood in NYC, completely from carbon-neutral biogas.

Read more about the mayor’s composting plan, and reaction, in the New York Times.