Every night when I wash dishes, I either throw food scraps down the garbage disposal or throw it in the trash.
Is it more sustainable to throw food scraps down the garbage disposal? I think things end up in the sewer system.
(Obviously composting would be the most sustainable)
You are asking to choose between two bad systems, and the least bad choice will depend on the surplus capacity of the sewage system vs space in the landfill.
Vancouver B.C. has now passed a building code against garburators. Reason: It doubled the amount of solid waste in the sewer system. The additional solids also made for more problems with blockages. We have friends there, who, despite having a yard the size of a commerative postage stamp compost nearly everything.
City of Edmonton has a very advanced garbage sorting system, and kitchen waste is composted in bulk, along with yard waste, wood scrap, and non-recycleable paper. (I buy a 60 cubic yard trailer of it per year for my tree farm)
Overall I would argue that a landfill tolerates 'too much' better than a sewage system does. City of Edmonton made the mistake years ago of having the storm drain system tied into the their sewage system. So at peak rainfall or snow melt, there is too much water to treat properly, and semi-raw sewaage goes into the river.
But there are better choices than either:
Vermiculture. A 70 liter tote makes an excellent worm farm, and will handle all of the non-meat kitchen waste a couple can generate. And the compost is good for the garden. If you live in a mild climate, the worm bucket can live on the balcony.
Having a city that composts -- agitate for it, and point to CoE as the example.
Keep guinea pigs. They will eat all the kitchen waste including the meat scraps. This is the traditional disposal method in Peru. Every now and then you have roast guinea pig for supper. Quite tasty. It will pick up the flavour of the dominant scraps fed it. I had some once that were fed on fish offal. Very odd to have something with the texture of turkey breast, and the taste of tuna.
Do conventional composting in the back yard. Takes more room that worms, but it's even easier. 7 pallets, available for the taking in any industrial area (ask first), and be set up as a 3 bin compost system in an afternoon.
If you twisted my arm to choose between those two options, I would say the garbage disposal is more sustainable.
Sewage goes through physical and biological process to remove contaminants and the treated water is returned to the ecosystem. Even though not all the sludge byproducts are reusable — some are only suitable for disposal — it's pretty safe to say that your ground up apple peels are contributing to the reusable side of the equation… typically a farm fertilizer.
In contrast, most household refuse is sent to a landfill. While there are efforts to make safer landfills, they are still essentially just piling the stuff up somewhere. Landfill materials don't biodegrade to any great degree, and the land isn't easily reclaimed for reuse. In essence, it is a less sustainable practice than the former.
Composting is still the best sustainable option.
Many in the sanitation treatment industry feel the garbage disposal was among the most troublesome inventions in the history of the modern home. Treatment facilities are designed to remove bacterial and viral contaminants, not solid wastes (grinding it and sending it into the sewer system does not change the fact that it is solid waste). Most plants have been retrofitted to remove the increased volume of food waste (among other things), but it is no where near as efficient as composting this waste stream.
Essentially, using a garbage disposal is another way to outsource waste removal without paying additionally for it, and it puts an undue burden on infrastructure. To see this process in action, and to see what happens when food waste is co-mingled with wastewater, I highly recommend taking a tour of your local treatment facility - usually this is a free service provided to citizens. For example, if you live in southern California, the Orange County Sanitation District and Los Angeles County Sanitation Districts will offer free tours:
Composting is relatively easy, although it does require a bit of maintenance. If you have a backyard, outdoor composting is definitely the preferred solution - there are plenty of websites out there that will provide instructions. If you live in an apartment or have limited space, consider worm composting. If done properly, there is no odor, and the end product (worm casting "poo") makes for perfect potting soil.
Composting (as above) should only be done with specific kinds of scraps - e.g. fruits, veggies, breads, egg shells, garden cuttings, etc. Do NOT add fats, oils, meats, or dairy products.
I had never heard of guinea pigs as a disposal method - cool idea! Along those same lines, many people in the U.S. are using chickens to achieve the same goal. Chickens will eat anything, including meats, fats, dairy products, cooked food, etc! But check your city or county ordinances to make sure this is approved in your area.
Try Bokashi composting: Done in the kitchen in an air-tight container--this is an anaerobic composting method or fermentation, not aerobic like conventional composting--surprisingly little odor is produced because nothing rots as happens in conventional composting. Can take a greater variety of wastes than conventional composting (including meat, bone, cooked food, etc.) Requires Bokashi bran for the particular microbes that work on the food scraps, called "Effective Microorganisms" or EM-1. Every time you add food scraps to your container you cover them with a handful of Bokashi bran, which contains the bacteria, fungi, etc. which break down the cellulose in the scraps. When the bucket is full, you set it aside for 2 weeks and then bury the contents in dirt. If you live in an apartment, you can use the material for container gardening or donate it to someone who has a garden or to a community garden.
What I like best about Bokashi is that it's pretty simple to do (compared with vermiculture, chickens or guinea pigs). And it demonstrates that one's food waste doesn't have to be regarded as waste at all. You can watch it become awesome fertilizer with most or all the nutrients intact (preserved by fermentation) to grow some new, tasty food.
Smart Cara is a device that sits on the kitchen counter. A powered/odorless composting system that converts food waste into organic fertilizer pellets in as little as 3 hours. This is probably the most environmental way if coupled with electricity derived from renewable sources.
As an alternative - biodegradable waste which is flushed down the toilet ends up in the sewer system, which can be extracted to be used as fertilizer - but not always - sometimes it's discarded.
Although if it is still not fully biodegraded, it will release methane gas. Future sewer networks may extract the gas for generating electricity as CO2 is a better greenhouse gas than methane and plants can take it in for photosynthesis.
