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​.face​book​.com/​G​r​a​n​d​A​r​m​y​P​l​a​z​a​G​r​e​e​n​m​a​r​ket

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/​h​t​m​l​/​n​y​c​w​a​s​t​e​l​e​s​s​/​h​t​m​l​/​r​e​s​o​u​r​c​e​s​/​w​c​s​_​o​r​g​a​n​i​c​s​.​s​h​tml

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.