In New York and elsewhere around the country, debates are underway with community composting and anaerobic digestion often seen as competing strategies. But both are needed.
Community composting provides many local benefits. It engages citizens to recognize how much waste they create and to become part of the solution while they help produce a product that improves local soil health. However, community compost sites release some amount of methane, depending on how the composting is done. The less airflow that gets into the decomposing organics, the more methane is emitted. Small-scale composting that is well-aerated produces very little methane, which is likely the case for most of the operations in NYC (and elsewhere).
By contrast, larger, commercial-scale compost sites (where organic wastes are often spread in large rows and periodically turned over) produce much more methane. According to NASA methane-monitoring satellite data from California, commercial-scale compost production facilities emit, on average, as much methane to the atmosphere as landfills. Landfills with no gas collection systems leak all their methane into the atmosphere, but even landfills with gas collection systems typically leak 30% of their methane, in some cases even 50%. The EPA’s goal is for landfills across the country to capture 70% of their methane emissions, meaning 30% is being written off as unattainable/unrealistic.
By contrast, anaerobic digesters, whether large or small, capture almost all the methane from the organic wastes they process. A 2021 UK study found the average amount of methane leakage from digesters is 3.7%. At well-operated modern facilities it is as low as 0.2%. Digesters also have the advantage of producing two valuable products instead of one: biogas, which can be used to generate electricity or be upgraded to renewable natural gas (RNG) fuel; and high-quality soil amendments similar to compost from the leftover solids called “digestate.”
Community compost sites only handle a small fraction of the enormous volume of inedible food waste that cities produce. In NYC, for example, the Newtown Creek wastewater plant’s digesters process as much food waste in two days as the Lower East Side Ecology Center’s composting does in a year.
Optimally, cities, including New York City, can benefit from both. Anaerobic digesters can process the vast majority of cities’ food waste. Community composting plays an important role, too, while building citizen awareness and pride of participation in addressing one of the country’s major environmental challenges.