What is composting?

Composting is an excellent alternative to waste disposal that diverts organic household waste (OHW) from landfills. There are two main processes in which OHW can be decomposed but the ultimate product is always a nutrient rich humus that can be used as a fertilizer.

The first type of decomposition is known as aerobic composting and it involves microorganisms that use oxygen to break down food. The by-product of this reaction includes CO2, water, heat, and ammonia.

The second process is known as anaerobic composting and it can only take place when there is no oxygen present. Microorganisms that work in the absence of oxygen are involved and they break down the waste to produce O2, CO2, ammonia, and methane. Whether you are composting at home or allowing the city to collect your OHW, both aerobic and anaerobic decomposition will occur but in very different concentrations.

For example, in Toronto, a portion of the collected waste is sent to an anaerobic composter. Here, the OHW is sorted using a hydro pulper that allows lighter contaminants (waste that cannot be composted) to float to the top and heavier contaminants to sink to the bottom where they are subsequently removed and sent to landfills. The remaining compostable waste is placed in an anaerobic environment which allows specific microorganisms to work to break-down the material and in the process, release methane and CO2. This biogas can be used to fuel the facility. A pre-compost substance (known as a digester solid) is also made and it is sent to a tertiary facility to be further composted aerobically into a humus. While the natural gas can only power the composting plant itself, there are hopes that the process can be improved so the gas can power collection vehicles as well.

Aerobic composting happens in greater abundance in family gardens and at some city centers. In this case, OHW is simply stacked and exposed to oxygen rich environments. Some anaerobic decomposition can still occur especially at the center of the pile where microorganisms are deprived of oxygen.  

Benefits of composting:

The most obvious benefit of composting is that it diverts waste from landfills. OHW is very toxic when left in landfills as it can contaminate groundwater and cause the release of methane gas that further pollutes the atmosphere. Using compost at home for the garden can also help to fight against pathogens, enrich soil, and overall, grow healthier plants. If you chose to compost at home, you are also helping to reduce greenhouse gas emissions released by vehicles transporting OHW from your home to composting facilities.

Are there any drawbacks to composting?

Composting is not perfect. It was previously mentioned that both types of composting produce CO2 which is a harmful greenhouse gas that contributes to global warming. Furthermore, anaerobic decomposition releases methane which is also a potent greenhouse gas. Anaerobic facilities contain any emitted greenhouse gases and do not allow them to pollute the environment. However, in home gardens the gases are released into the atmosphere and can contribute to global warming. This does not mean that you should be deterred from composting at home. You can take certain precautions to minimize the amount of greenhouse gases emitted by maintaining a moderate pile that does not get too big and not excessively turning your pile.

Tips and tricks for composting:

If you are starting your own compost pile:

1. Compost can actually be damaging to your garden if you do not wait long enough for it to mature. Immature compost is full of phytotoxins that can kill plants. To test if your pile is mature, apply it to some of your fast-growing crops (i.e. radishes) and observe the effect it has on them.
2. Your compost pile needs 3 key substances: oxygen, carbon, and nitrogen.
   • Carbon can be accessed from plant material like dried leaves, branches, stems, and paper bags. You should have much more carbon-rich material than nitrogen-rich material.
   • Nitrogen can be accessed from table scraps, grass clippings, coffee filters, and coffee grounds.
3. To speed up the composting process you can…
   • Turn your pile which helps to replenish oxygen-deprived areas and allows microorganisms to further break down the waste
   • Break bigger waste material into smaller parts
4. Your compost pile should be fairly moist so that when squeezed, it can maintain its shape but is not so runny that it releases extra liquid. You can moisten your pile by sprinkling it with hose water or dry it up by removing the lid and exposing it to the sun.
5. To avoid pests DO NOT put animal waste or bones in your compost pile. These may be items that you include in city-collected compost instead.
6. Do not include any diseased or infected plants in your compost.
7. If you wish to start your own compost pile, there are a number of different receptacles you can use and methods you can follow. A good resource to get you going is from the EPA: https://www.epa.gov/recycle/composting-home

If you are collecting organic waste for the city:

1. Minimize the amount of plastic you use to line your compost receptacle because the more plastic that is sent to the decomposition facility, the less potent the resultant humus.
2. Make sure to check what type of sorting mechanism and composting method your city uses. Hydro pulpers sort materials based on how they behave in water. So compostable plastics will still be counted as contaminants and will be removed from the compost pile and sent to landfills instead. You also cannot put compostable plastic in the recycling.
3. Generally accepted food waste includes: fruits, vegetables, meats including bones, breads, dairy products, cakes, animal waste, plant waste, coffee grounds and filters but NOT coffee pods, diapers, soiled paper INCLUDING ice cream and popcorn containers, flour and sugar bags, and soiled tissues that have not been used with chemicals or cleaning supplies

---

Referenced Material:

Andersen, J. K., Boldrin, A., Christensen, T. H., Scheutz, C. (2010). Greenhouse gas emissions from home composting of organic household waste. Waste Management, 30(12): 2475-2482. https://doi.org/10.1016/j.wasman.2010.07.004

Chadar, S. N., Chadar, K., Singh, M. (2018). Composting as an eco-friendly method to recycle organic waste. Progress in Petrochemical Science, 2(5). doi: 10.31031/PPS.2018.02.000548

Fitzpatrick, G. E. & Duke, E. R. (1994). Building and maintaining a compost pile for the home garden. Proceedings of the Florida State Horticultural Society, 107: 385-387. Retrieved from: https://journals.flvc.org/fshs/article/download/92441/88633

N. A. Composting: How to make nutrient-rich garden ‘gold’ in the composter that will help your garden thrive. Earth Easy. [internet]. Accessed 2020, May 25. Retrieved from: https://learn.eartheasy.com/guides/composting/#compostbin

N.A. What goes in the green bin? City of Toronto [internet]. Accessed 2020, May 25. Retrieved from: https://www.toronto.ca/services-payments/recycling-organics-garbage/houses/what-goes-in-my-green-bin/