A 1990s study by New York City showed that in-sink garbage disposals punch above their weight in environmental benefits. So why are they so rare in the city? Misconceptions, apparently:
The city installed more than 200 of the devices in select city apartments for a 21-month trial run; they then compared apartment units that had disposers with disposer-less units in the same building. Careful analyses from this study and others formed the basis of DEP’s report: the projected impact of citywide disposal legalization was minimal, and the Department estimated a $4 million savings in solid waste export costs.
Waste disposal is a thorny problem even in small towns, but for New York City, the trash pile continues to mount: The Department of Sanitation handles nearly 10,000 tons per day of waste generated by residents and nonprofit corporations, and the cost of disposal in Manhattan has grown from $300 million in 2005 to about $400 million today. Commercial establishments are serviced by private carting firms who also collect about 10,000 tons per day. All of that trash must be transported to landfills—often hundreds of miles outside the city—where it is converted into methane gas.
[L]andlords may still be reluctant to install the fixtures because of first-time installation costs (which can exceed $600), concerns about maintenance, or because they simply aren’t aware disposers are permitted to begin with. Perhaps the greatest block to in-sink disposal adoption, however, are our own misconceptions about them. Water and electricity use are minimal (according to InSinkerator, disposers account for less than 1 percent of a household’s daily water usage, and the total energy cost is about $0.50 per year); the devices don’t require much maintenance and often last a decade or more; clogged pipes are rare because scraps are entirely pulverized; almost everything can go down the disposer (veggies, fruit, meat, pizza), and newer models are nearly silent (and not deadly).
They also help your kitchen garbage smell better. But that's nothing compared to recapturing millions of tons of methane.