Grindage

July 13, 2007 1:00 PM

The local council is urging residents who live in a flat to get a food waste disposer (garbage disposal). Are these units an environmentally sound alternative to composting?

In the US, I was used to having an "Insinkerator" and I miss it. But, isn't it bad for the sewage treatment plants? Should I be trying to convince my neighbours to share a composting bin with me [I have no garden at all, or else I would've already started composting]?

posted by chuckdarwin to home & garden (13 answers total)

There are lots worse things going into sewage treatment plants than coffee grounds and eggshells! People dispose of a lot of really weird stuff via the plumbing. I think if you don't actually have a garden or landscaping to use compost in, a compost bin is just going to attract bugs. I compost and it does take a bit of upkeep (adding carbon & nitrogen items & turning it) to keep the piles from smelling foul.
posted by pluckysparrow at 1:11 PM on July 13, 2007

It's not particularly bad for the treatment plant (they've got other things to worry about), but they're not preferable to composting (for vegetable matter, anyhow).

Also, in my limited experience, they seem to be prone to leaks -- my current condo association forbids their installation due to bad experience with repeated water damage (regardless of brand, and regardless of plumber qualifications).
posted by aramaic at 1:12 PM on July 13, 2007

Both ways keep bulk out of your local landfill and biodegrade the food efficiently. However, by putting it in the sewer that sweet rich fertilizer you are making goes into lakes and streams to fuel algae and weeds. Better to put that in your garden and skip the chemical fertilizer. Put the meat down the disposal though, it can attract animals and bugs and composts slowly.
posted by caddis at 1:17 PM on July 13, 2007

What about a trash compactor? Reduces the volume, if not the weight of trash.
posted by blue_beetle at 1:33 PM on July 13, 2007

Oh, I should've said that we're pescetarians, caddis...
posted by chuckdarwin at 1:45 PM on July 13, 2007

I learned a new word today.
posted by caddis at 1:57 PM on July 13, 2007

In the sewer, a lot of the food waste probably settles out in the primary settlement tanks as "sewage sludge." Usually, in the US, sludge is sent to a landfill, since it often has stuff like metals in it (especially if the wastewater plant also treats stormwater runoff from streets).

What's left after settlement goes on to secondary treatment, where bacteria (usually aerobic) digest the waste. I'm not exactly sure how the carbon emissions in this digestion compare to those of composting, but I suspect they're higher since the goal is to make the water free of organic matter (biological oxygen demand, or BOD). So, all the carbon and nutrients in the food waste get converted to CO2 or taken up by the bacteria. Then most of those bacteria are also landfilled.

In short, all the biological matter in sewage ends up either in the air (as CO2 or methane) or the landfill, rather than in soil where ideally it will boost soil fertility, get taken up by plants, etc. So it probably is a bit better to compost your food waste, especially if you can find someone who'd like some planting soil!

One diagram explaining the process is here.
posted by salvia at 2:15 PM on July 13, 2007

Usually, in the US, sludge is sent to a landfill, since it often has stuff like metals in it (especially if the wastewater plant also treats stormwater runoff from streets).

In some cases, yes. There are still plenty of places in the midwest, though, where that sludge is sprayed onto fields as fertilizer.
posted by chrisamiller at 2:59 PM on July 13, 2007

Well, composting is certainly the most direct way to return the nutrients in your garbage to the soil and put it to use. It also takes the least energy to process your waste. I would say composting is better for the environment overall than using the garbage disposal.

However, there's not necessarily anything wrong with using a garbage disposal. As described above, it goes through the sewage treatment process, and many of the solid parts will end up in a landfill, where they will be buried and probably not decompose for many many years. It's a slower and more energy-intensive process. Whether or not using a garbage disposal is better or worse than just dumping it in the trash can and having it go through the solid waste process - that I do not know. (And not your question.)

No, disposals are not environmentally better than composting.
No, disposals are not bad for sewage treatment plants.
Yes, you should convince your neighbors to share in a composting bin.
posted by gingerbeer at 3:12 PM on July 13, 2007

In some cases, yes. There are still plenty of places in the midwest, though, where that sludge is sprayed onto fields as fertilizer.

You can put some on your lawn too, and if you play golf it is most likely on your golf course - Milorganite.

jgingerbeer, if it is going to end up in a landfill, why not just throw it in your garbage can? It does no benefit to the environment in a landfill. The rest of the stuff in there is so nasty that it can not be used to fertilize crops or lawns. If you compost it then you can use it for fertilizing your garden. Of course, if you live in Milwaukee, then you can still put it on your garden or lawn.
posted by caddis at 3:35 PM on July 13, 2007

Like chrisamiller said, there are many places where the sludge is used as fertilizer. Here they spray it on city owned fields and the city grows hay and sells it to farmers for their cows.
posted by wierdo at 3:51 PM on July 13, 2007

A lot of municipalities offer community composting with kerbside pickup and free compost for gardeners.
posted by BrotherCaine at 9:43 PM on July 13, 2007

Running a worm farm gives you all the benefits of composting, with a lot less work. I wrap my food scraps into newspaper parcels and dump the whole thing in the worm farm - the newspaper helps with the carbon/nitrogen balance, and worms breed up in its layers. The worms gobble up anything potentially smelly before it gets anywhere near offensive.
posted by flabdablet at 3:18 AM on July 14, 2007 [3 favorites]