A garbage disposal, waste disposal unit, or garburator / garbarator (Canada) is a device, usually electrically-powered, installed under a kitchen sink between the sink's drain and the trap which shreds food waste into pieces small enough to pass through plumbing.
Some local authorities in Britain subsidise the purchase of garbage disposal units in order to reduce the amount of waste going to landfill.
Use of these food processing units increases household water use, but their impact on business water use (in restaurants) is generally not statistically significant.
Many standard disposal units allow a dishwasher to be connected, and some more expensive dishwashers are equipped with a small built-in garbage disposal units, making it unnecessary to scrape plates before washing them.
The garbage disposal was invented in 1927 by John W. Hammes. He was an architect working in Racine, Wisconsin. After eleven years of development, his InSinkErator company put his disposer on the market in 1938.
In many cities in the United States the municipal sewage system had regulations prohibiting running food waste (garbage) into the system. InSinkErator spent considerable effort, and was highly successful in convincing many localities to rescind these prohibitions. Many localities mandated the use of disposers. For many years, garbage disposals were illegal in New York City because of a perceived threat of damage to the city's sewer system. The ban was rescinded on September 11, 1997 by local law 1997/071 which amended section 24-518.1, NYC Administrative code. In 2008, the city of Raleigh, North Carolina attempted a ban on the replacement and installation of garbage disposals which also extended to outlying towns sharing the city's municipal sewage system, although rescinded. Violations of this ban faced civil penalties of up to $25,000 per day and interruption of water and sewer services.
Garbage disposal units became popular in American kitchens of the better-off in the 1970s and 1980s. The EU prohibited the use generally with the option for member countries to make exceptions, and local authorities generally emphasize the prohibition: the reason is supposedly the additional load on sewage treatment plants which would make sewage treatment more expensive than the composting of kitchen waste. In the U.S. 47% of homes had disposal units as of 2007, but in the United Kingdom this was only 6%.
A high-torque, insulated electric motor, usually rated at 200–750 watts (¼ to 1 horsepower) for a domestic unit, spins a circular turntable mounted horizontally above it. Induction motors rotate at 1,400–1,800 rpm and have low starting torque; commutator motors rotate at higher speeds (about 2,800 rpm), have high starting torque, and are usually lighter. However commutator motors are noisier than induction motors, partially due to the higher speeds and partially because the commutator brushes rub on the slotted armature. The higher starting torque of those appliances with a permanent magnet motor secures in most cases that there will be no blockage.
The added weight and size of induction motors might be of concern. Many models have some degree of sound insulation.
The turntable is surrounded by a shredder ring, which has sharp slots. The food waste sits on the turntable and through centrifugal force is forced to its perimeter and through the shredder ring. The turntable has a number of swiveling lugs—similar to little hammers attached to its topside—which assist in forcing the waste through the shredder. Except for special models, most of the food waste disposers do not have any sharp blades or scissors.
Waste is fed into a chamber above the turntable and drops on the turntable. The chamber may have a rubber partial closure through which waste can be pushed without letting cutlery and other objects fall in, but essentially the chamber is open at the top, and there is access to the turntable. This is useful in the case of a jam: The turntable can be forced round by pushing with a wooden spoon handle or similar object until the jam clears. Waste that cannot be ground successfully can be removed manually.
Most units are of the continuous-feed type, allowing waste to be added as the unit runs. Batch-feed models are also available with a lid that must be locked before operation, making it impossible to run the machine when a user is trying to clear a jam by hand and preventing cutlery, etc. from falling in.
Some commercial and high-end domestic disposals also have an undercutter blade that revolves below the turntable and chops the ground waste, including fibrous material which could cause a drain clog, finer. These disposals can handle fibrous waste such as artichoke leaves that cannot be successfully ground in a standard disposal. Waste disposal units may jam but can usually be cleared either by forcing the turntable round from above or by turning the motor using a hex-key wrench inserted into the motor shaft from below. Very hard objects accidentally or deliberately introduced, such as metal cutlery, can damage the waste disposal unit and become damaged themselves. More problematic are drain blockages caused by shredded waste that is fibrous (artichoke leaves) or starchy (potato peelings).
Some higher-end units have automatic reversing. By using a slightly more-complicated centrifugal starting switch, the split-phase motor rotates in the opposite direction from the previous run each time it is started. This can clear minor jams but is claimed to be unnecessary by some manufacturers: Since the late 1970s most disposal units have swivel impellers which make reversing unnecessary.
Another kind of garbage disposal unit is powered by water pressure rather than electricity and does not pose an electrical hazard. Instead of the turntable and grind ring described above, an alternative machine has a water-powered unit with an oscillating piston with blades attached to chop the waste into fine pieces. Because of this cutting action, they can handle fibrous waste. Water-powered units take longer than electric ones for a given amount of waste and need fairly high water pressure to function properly.
Cold water should always be kept running when the disposal is switched on to prevent damage to the blades and wash away the chopped waste without allowing it to build up and clog the drains. Hot water tends to dissolve easily-flushed solid shredded pieces of fat, which can then solidify and block the drain.
Provision must be made to supply and switch power to the waste disposal unit. A conventional electric switch can be used, which requires wiring to be installed and poses a potential electric shock hazard if used with wet hands. An air switch which delivers a puff of air to operate an electric switch remote from the operator is safer. Alternatively, a wireless remote control switch can be used.
If a garbage disposal is discovered to have a "frozen lug", or a hammer that does not move freely, it is recommended that the user feed smaller bones such as those from chicken, through the unit. As seen on an episode of the TV show "How It's Made", ISE company tests its units by feeding frozen steer bones through a sample batch of disposal units, so one does not need fear damage to a unit in good condition with chicken bones. Many repair technicians recommend a weekly feeding of a batch of ice cubes through a running disposer to maintain good cleanliness. This will assist in keeping the lugs or hammers rotating freely and remove any build-up of deposits and minerals. Never feed glass into a garbage disposal.
Be aware that disposers used in conjunction with septic systems will add to the load of the system, and may cause more frequent septic pumping or overflow of sewage into one's yard. Special garbage disposers are marketed toward septic system users that feature an enzyme-adding system that is purported to aid in degradation of food waste while in the septic system.
Induction and commutator motors each have advantages and disadvantages. Feed can be continuous or batched.
Some manufacturers use standard mountings for all their models, making it very easy to replace a unit by any model of the same brand.