It should be mentioned that much of the food being thrown into landfills is still perfectly fit for human consumption.  Large quantities of edible food are regularly disposed of simply for reasons of convenience to the food industry – supermarkets must routinely be clearing their shelves of older produce to make space for new shipments as there is little or no market for its re-sale and no means to accordingly and finely adjust the shipment of food on the production end.   While I strongly advocate for composting food that has spoiled, human consumption is always a preferable and “higher use” than either feeding to animals or composting.  The efforts of food recovery organizations and food pantries are critical to achieving the collection and distribution of this otherwise squandered resource.  This view is supported by the federal government’s “food diversion” pyramids that propose a hierarchy of preferred uses for unsellable food (Papargyropoulou, 2014).  For food wastes that are unfit for human consumption, use as an animal feed or for composting are the next most preferable choices.  While the focus of this chapter is on composting, I will mention that chickens, ducks, rabbits, and goats are highly appropriate for urban environments and are capable of rapidly digesting food wastes.  The manures they produce are recoverable and can themselves be composted or applied directly to soils, enriching them in much the same way that finished compost will.  An additional benefit of animal composting is that added-value products such as eggs, milk, and meat can be co-produced.

For food wastes that are unfit for humans and in situations where it is not an option to feed them to animals, composting is the preferred method of processing.  A compost pile is essentially a microbial reactor.  When organic wastes are mixed to achieve the correct ratio of carbonaceous to nitrogenenous materials in a pile of at minimum of a cubic yard, and when sufficient oxygen and moisture are present, the composting process begins.  Indigenous bacteria will begin consuming the wastes, generating heat in the process that accelerates the rate of decomposition.  This period of active decomposition can last anywhere between three weeks to several months, depending on the availability of oxygen, moisture, nutrients, etc.  During this period a nearly fifty percent reduction in the volume of the compost pile occurs, with much of its mass being lost to an aqueous leachate or escaping in the form of carbon dioxide.  Following the active phase and once the temperature of the pile drops, other organisms become active in the pile including fungi, actinomycetes, nematodes, worms, micro-invetebrates, etc.  This multi-species sympoeitic ecosystem gives the compost a final polish, resulting in a finished product that is dark, moist, crumbly, pH neutral, and smells sweetly of earth, an example of the “Power of the Humusites for a Habitable Multispecies Muddle” (Haraway, 2016).  Teeming with nutrients and microbial life, the finished compost can then be used as an amendment to garden soils (Campbell, 1998).

It is important to mention that because composting is an aerobic process, no methane and only carbon dioxide is produced (although methane production can result in a poorly constructed compost pile).  As mentioned previously, carbon dioxide is a far less potent greenhouse gas than methane.  On account of growing awareness and activism related to climate change, however, an erroneous belief has emerged that carbon dioxide resulting from any process will contribute to climate change and is therefore undesirable.  Composting provides a good opportunity to educate citizens about the planet’s carbon cycle, particularly the difference between carbon neutral and carbon positive practices.  A clear distinction must be made between carbon produced from the biological processes of carbon-based life forms presently on the planet’s surface (breathing, defecating, dying), and carbon originating from ancient photosynthetic organisms-turned-fossil fuels and brought to the planet’s surface.  Only the latter will result in an increase of atmospheric CO2 concentrations.