To Compost or Digest - That is the Question

According to the Environmental Protection Agency (EPA), food scraps are the second largest component of household trash with over 30 million tons of food waste making their way into landfills each year. Food scraps and other organic materials such as yard trimmings typically decompose into compost, a nutrient-rich soil, through one of two processes:

  • Aerobic decomposition - Occurs when oxygen (O2) is available to the organisms and microbes responsible for breaking down organic matter. This process is typically faster than anaerobic decomposition and primarily generates carbon dioxide (CO2) and water (H2O).
  • Anaerobic decomposition - Occurs when O2 is absent (such as in a completely sealed container or beneath a landfill) and methane-producing bacteria take over the decomposition process. This process primarily generates the greenhouse gas (GHG), methane.

In landfills, decomposition typically starts out as an aerobic process, but as conditions change and O2 becomes scarce, anaerobic decomposition takes over, leading to high levels of methane production. Pound for pound, methane is up to 25 times more effective at trapping heat in the atmosphere than carbon dioxide (CO2), making landfills the third largest source of human-related greenhouse gas (GHG) emissions in the United States.

Diverting food waste from landfills and composting it instead offers a myriad of benefits beyond GHG emission reductions. For a composter to be effective and promote the breakdown of the food scraps inside, it must provide drainage and air circulation. There are several composting options available today:

  • Vermicomposting
  • Aerated Windrow Composting
  • Aerated Static Pile Composting
  • In-Vessel Composting
  • Compost Digester

Vermicomposting, aerated windrow composting, aerated static pile composting, and in-vessel composting all create a nutrient-rich soil within a specified period of time (some processes take longer than others) that can be used in landscaping and organic farming.

The Compost Digester on the other hand primarily digests the organic material and leaves little behind. A compost digester is an almost entirely closed container that enhances the decay of organic material. Aside from the lid at the top where food waste is dropped, a digester has no openings other than the bottom basket where liquid drains into the ground as compost water. Compost digesters can compost meat, bones, some dairy products, and even pet feces, making it advantageous over traditional open-air piles.

For backcountry facilities, the compost digester is an excellent means of preventing waste, increasing recycling rate, and because the majority of the food waste is digested, it does not need to be emptied on a regular basis, making it very low maintenance.