Is My In-Sink Garbage Disposal Eco-Friendly?

Woman composting organic kitchen waste

KatarzynaBialasiewicz / Getty Images 

Dear Pablo, I have been wondering for some time if I should be using the garbage disposal or not. The InSinkErator website talks about the environmental benefits of disposers, but is this just greenwash?

According to my favorite wastewater engineer, "household garbage disposals were the worst thing to ever hit the wastewater industry. Cities will eventually outlaw them for any new construction (as with what's happened with water softeners)." Apparently I struck a nerve with my question, let's see what's behind that response. On their web page about the environmental benefits of disposals, InSinkErator makes the following statement:

The world’s garbage flows from many different sources, in various forms, and it only makes sense that getting rid of it requires a variety of approaches. While there is no waste management silver bullet, food waste disposals are both a practical and environmentally responsible way to help manage the more than 31 million tons of solid waste represented by food scraps generated in the US each year.
Trucking food waste to landfills and incinerating it generates emissions. In landfills food scraps decompose quickly, producing methane, a greenhouse gas at least 21 times more potent in trapping heat in the atmosphere than carbon dioxide, plus an acidic liquid residue (leachate) that can seep into ground water. Home composting (when done properly) makes sense, but it’s not always practical for all people everywhere – in crowded urban settings, in high-rise buildings, in frigid weather. Using disposals complements composting.

True, in the absence of oxygen moist organic materials turn into biogas, which is 50-70% methane and methane is 21 times more effective than carbon dioxide at altering our climate (or 25 if you go with the IPCC's most recent report). But what happens to food waste that is washed down the drain? According to InSinkErator, 70% of food scraps are water, but some of the remaining 30% are solids that are screened out at the entrance to your waste water treatment plant. In most cases this material is also sent to the landfill, where it will decompose in the absence of oxygen, creating methane.

Modern Landfill Regulations

The EPA requires that new and modified landfills designed to hold 2.5 million cubic meters install gas collection and control systems and California has this requirement for all new landfills. Some landfills even use the methane to generate electricity or send it to natural gas pipelines (Methane = Natural Gas). Landfills that are not legally required to do so can earn greenhouse gas emission reduction credits for capturing emissions. So far no state (that I have been able to find) requires the capture and destruction of methane gas emitted by waste water treatment plants. The dissolved solids that make it in to the waste water treatment plant are either turned into carbon dioxide or methane by enzymes. But this additional work that the wastewater treatment plant has to do carries a cost. Increased biological oxygen demand (BOD) and dissolved solids levels increase the amount of treatment required, meaning more energy and more chemicals.

Food Waste Problems

Another issue is that food waste increases the likelihood of clogs, especially if the food waste contains unsaturated fats, which solidify at room temperature and can build up inside pipes. Besides being inconvenient for homeowners and city maintenance workers blockages cause roughly 75% of all sanitary sewer overflows, where untreated sewage is diverted from the wastewater treatment plant and usually into a body of water. The San Francisco Public Utility Commission spends about $3.5 million per year just in responding to grease-related blockages. They have roughly 900 miles of pipeline, so that's about almost $4000 per mile.

In-sink garbage disposer proponents claim that sending food waste down the drain decreases the amount of waste trucked to the landfill in large diesel-powered trucks. However, the conveyance of food waste through a pipe requires a lot of water and that water has to come from somewhere. According to a 2005 California Energy Commission report, 19% of California’s electricity use, and 32% of its natural gas use is for pumping water and wastewater! So, not only is water a scarce resource that should be conserved, but pumping it requires a lot of energy and, in California at least, contributes a significant amount to global warming.

So, what do you do with all that food waste? Composting comes to mind, but as the InSinkErator website claimed: "Home composting (when done properly) makes sense, but it’s not always practical for all people everywhere – in crowded urban settings, in high-rise buildings, in frigid weather." Apparently they have never heard of the NatureMill indoor automatic composter. This product, made from recycled materials, includes a small heater and mixer (uses only $0.50 of electricity per month) to maintain industrial-grade composting conditions. This means that you can even compost meat, dairy, and fish in it, which is typically a composting faux pas. The unit fits under your sink or on your fire escape, so even the most urban of us can avoid sending food waste down the drain while producing up to 120 pounds per month of rich organic compost each month.

Though convenient for quickly disposing of the contents of that mystery container that has been in your fridge for months, the in-sink garbage disposal is certainly not the greenest way to deal with your kitchen waste.