This time it’s San Francisco, one of the first cities in the country to adopt a mandatory composting and recycling ordinance. The city has even moved to implement fines of up to $1,000 to buildings, mostly large waste producers, that fail to comply with the law. The hope is that by 2020, none of San Francisco’s annual two million tons of solid waste will make its way to a landfill.

Ambitious? Certainly. But how do they plan to deal with all of this compostable solid waste?

The answer lies in anaerobic digestion, the same process used to treat sludge at wastewater treatment plants. Anaerobic digestion is the process of microorganisms breaking down organic waste in an oxygen free environment. If this decomposition is allowed to occur in an open air environment, at either a landfill or other facility, it releases copious amounts of methane into the atmosphere, a greenhouse gas 21 times more potent than CO2. 

However, when the process is confined, its byproducts can be contained. The first, methane gas, is captured and used to create energy. This energy is most often used to power the facility itself, but can also be sent to the grid. The other byproduct, digestate, is a nutrient rich solid that can be used for fertilizer.
Obviously these facilities require some upfront cost to expand their capacity. However, the program’s potential to create jobs, help the environment and provide long term benefits far outweigh the costs!