Composting has many benefits beyond dealing with waste
The U.S. Environmental Protection Agency lists several benefits of composting:
- Compost reduces and in some cases eliminates the need for chemical fertilizers.
- Compost promotes higher yields of agricultural crops.
- Compost can help aid reforestation, wetlands restoration, and habitat revitalization efforts by improving contaminated, compacted, and marginal soils.
- Compost can be used to remediate soils contaminated by hazardous waste in a cost effective manner.
- Compost can provide cost savings over conventional soil, water and air pollution remediation technologies, where applicable.
- Compost enhances water retention in soils.
- Compost provides carbon sequestration.
(They also mentioned reduced methane emissions, but if we're comparing composting to incineration where the methane would be burned, this doesn't apply.)
Composting is more efficient than incineration...
... for by-products...
Some of the energy you'd produce from burning compost would go to producing the very things that compost becomes -- humus, fertilizer, and topsoil -- along with the packaging materials and transportation.
By producing those products directly from compost, you skip the inefficiencies in each of these steps:
Compost -> heat -> energy -> production, packaging, transport -> garden/farm
Instead, you can just do this:
Compost -> garden/farm
... and for energy
About 23% of municipal solid waste (MSW) is comprised of food and yard waste that could be composted, according to the report "Waste Incineration and Public Health" from the National Research Council.
A lot of these materials also have a high moisture content. This moisture has to be removed (i.e. evaporated) before it can burn and produce energy, a step which in itself requires energy. From "Pyrolysis technologies for municipal solid waste: A review":
During pyrolysis [i.e. incineration] the feedstock will not undergo thermal
decomposition before its moisture is vaporized [...] therefore to reduce this part of energy, MSW components with high moisture content such as food wastes, biomass are suggested to be separate before pyrolysis. In addition, in order to reduce this portion of energy a drying step is usually adopted in front of pyrolysis reactor.
So by removing compostable food waste, incinerators can be made simpler and more efficient.
Additionally, due to metal content, the ash from incinerators requires special handling and is one of the highest costs, according to the U.S. Department of Energy report "Waste-to-Energy from
Municipal Solid Wastes". Removing content that doesn't have any metal (compostable waste) reduces these operating costs.
With a digester, composting can still produce energy
Large operations can employ a methane digester to do anaerobic digestion, which, according to Wikipedia:
is widely used as a source of renewable energy. The process produces a biogas, consisting of methane, carbon dioxide, and traces of other 'contaminant' gases. This biogas can be used directly as fuel, in combined heat and power gas engines or upgraded to natural gas-quality biomethane. The nutrient-rich digestate also produced can be used as fertilizer.
(You can even purchase digesters for use at home, though they are probably impractical and expensive for most homes.)
Backyard composting is convenient
Personally, I use a backyard composter because it keeps the stinky food out of my garbage can, reduces how often I have to take out the trash, and produces nutrient-rich humus that I supplement my vegetable garden with each year, producing better yields for less money.
Municipal composting provides economic benefits
MIT's Urban Sustainability Assessment produced a report titled "Municipal Curbside Compostables Collection: What Works and Why" which includes data on specific benefits of centralized municipal composting, including (paraphrased from Appendix A, "The Benefits of Composting"):
- Diverting materials away from landfills, which can help meet landfill reduction targets and save on landfill fees.
- Improved incinerator efficiency for the leftover waste (see above).
- Locally owned/operated composting facilities reduce the need to transport waste to distant landfills and can create local job opportunities.
- Many municipalities maintain parks, open spaces, and even some farms and gardens. Owning their own composting operations can reduce the costs of soil and soil amendments and increase productivity.