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A garbage disposal unit (also known as a waste disposal unit, garbage disposer, garburator etc.) is a device, usually electrically powered, installed under a
kitchen sink Kitchen sink may refer to: * ''Freaks of Nature'' (film), a 2015 comedy horror film, also known as ''Kitchen Sink'' * ''Kitchen Sink'', a 1989 horror short directed by Alison Maclean * ''Kitchen Sink'' (TV series), cookery series on Food Network ...
between the sink's
drain Drain may refer to: Objects and processes * Drain (plumbing), a fixture that provides an exit-point for waste water or for water that is to be re-circulated on the side of a road * Drain (surgery), a tube used to remove pus or other fluids from ...
and the
trap A trap is a mechanical device used to capture or restrain an animal for purposes such as hunting, pest control, or ecological research. Trap or TRAP may also refer to: Art and entertainment Films and television * ''Trap'' (2015 film), Fil ...
. The disposal unit shreds food waste into pieces small enough—generally less than in diameter—to pass through
plumbing Plumbing is any system that conveys fluids for a wide range of applications. Plumbing uses pipes, valves, plumbing fixtures, tanks, and other apparatuses to convey fluids. Heating and cooling (HVAC), waste removal, and potable water delivery ...
.


History

The garbage disposal unit was invented in 1927 by John W. Hammes, an
architect An architect is a person who plans, designs and oversees the construction of buildings. To practice architecture means to provide services in connection with the design of buildings and the space within the site surrounding the buildings that h ...
working in
Racine, Wisconsin Racine ( ) is a city in and the county seat of Racine County, Wisconsin, United States. It is located on the shore of Lake Michigan at the mouth of the Root River. Racine is situated 22 miles (35 km) south of Milwaukee and approximately 60 ...
. He applied for a patent in 1933 that was issued in 1935. His
InSinkErator InSinkErator is an American company and brand name known for producing instant hot water dispensers and food waste disposal systems, generally called "garbage disposals" or "garbage disposers". History Architect John W. Hammes founded the comp ...
company put his disposer on the market in 1940. Hammes' claim is disputed, as General Electric introduced a garbage disposal unit in 1935, known as the Disposall. In many cities in the United States in the 1930s and the 1940s, the municipal sewage system had regulations prohibiting placing
food waste Food loss and waste is food that is not eaten. The causes of food waste or loss are numerous and occur throughout the food system, during production, processing, distribution, retail and food service sales, and consumption. Overall, about o ...
(garbage) into the system. InSinkErator spent considerable effort, and was highly successful in convincing many localities to rescind these prohibitions. Many localities in the United States prohibited the use of disposers. For many years, garbage disposers were illegal in
New York City New York, often called New York City or NYC, is the List of United States cities by population, most populous city in the United States. With a 2020 population of 8,804,190 distributed over , New York City is also the L ...
because of a perceived threat of damage to the city's sewer system. After a 21-month study with the NYC Department of Environmental Protection, the ban was rescinded in 1997 by local law 1997/071, which amended section 24-518.1, NYC Administrative Code. In 2008, the city of
Raleigh, North Carolina Raleigh (; ) is the capital city of the state of North Carolina and the List of North Carolina county seats, seat of Wake County, North Carolina, Wake County in the United States. It is the List of municipalities in North Carolina, second-most ...
attempted a ban on the replacement and installation of garbage disposers, which also extended to outlying towns sharing the city's municipal sewage system, but rescinded the ban one month later.


Adoption

In the United States, some 50% of homes had disposal units as of 2009, compared with only 6% in the
United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and North ...
and 3% in Canada. In Sweden, some municipalities encourage the installation of disposers in order to increase the production of biogas. Some local authorities in Britain subsidize the purchase of garbage disposal units in order to reduce the amount of waste going to landfill.


Rationale

Food scraps range from 10% to 20% of household waste, and are a problematic component of municipal waste, creating public health, sanitation and environmental problems at each step, beginning with internal storage and followed by truck-based collection. Burned in
waste-to-energy Waste-to-energy (WtE) or energy-from-waste (EfW) is the process of generating energy in the form of electricity and/or heat from the primary treatment of waste, or the processing of waste into a fuel source. WtE is a form of energy recovery. Mo ...
facilities, the high water-content of food scraps means that their heating and burning consumes more
energy In physics, energy (from Ancient Greek: ἐνέργεια, ''enérgeia'', “activity”) is the quantitative property that is transferred to a body or to a physical system, recognizable in the performance of work and in the form of heat a ...
than it generates; buried in
landfill A landfill site, also known as a tip, dump, rubbish dump, garbage dump, or dumping ground, is a site for the disposal of waste materials. Landfill is the oldest and most common form of waste disposal, although the systematic burial of the waste ...
s, food scraps decompose and generate
methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Eart ...
gas, a
greenhouse gas A greenhouse gas (GHG or GhG) is a gas that Absorption (electromagnetic radiation), absorbs and Emission (electromagnetic radiation), emits radiant energy within the thermal infrared range, causing the greenhouse effect. The primary greenhouse ...
that contributes to climate change. The premise behind the proper use of a disposer is to effectively regard food scraps as liquid (averaging 70% water, like human waste), and use existing infrastructure (underground sewers and wastewater treatment plants) for its management. Modern wastewater plants are effective at processing organic solids into fertilizer products (known as
biosolids Biosolids are solid organic matter recovered from a sewage treatment process and used as fertilizer. In the past, it was common for farmers to use animal manure to improve their soil fertility. In the 1920s, the farming community began also to use ...
), with advanced facilities also capturing methane for energy production.


Operation

A high-
torque In physics and mechanics, torque is the rotational equivalent of linear force. It is also referred to as the moment of force (also abbreviated to moment). It represents the capability of a force to produce change in the rotational motion of th ...
, insulated
electric motor An electric motor is an Electric machine, electrical machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor's magnetic field and electric current in a Electromagneti ...
, usually rated at for a domestic unit, spins a circular turntable mounted horizontally above it. Induction motors rotate at 1,400–2,800
rpm Revolutions per minute (abbreviated rpm, RPM, rev/min, r/min, or with the notation min−1) is a unit of rotational speed or rotational frequency for rotating machines. Standards ISO 80000-3:2019 defines a unit of rotation as the dimensionl ...
and have a range of starting torques, depending on the method of starting used. The added weight and size of induction motors may be of concern, depending on the available installation space and construction of the sink bowl.
Universal motor The universal motor is a type of electric motor that can operate on either AC or DC power and uses an electromagnet as its stator to create its magnetic field. It is a commutated series-wound motor where the stator's field coils are connected in ...
s, also known as series-wound motors, rotate at higher speeds, have high starting torque, and are usually lighter, but are noisier than induction motors, partially due to the higher speeds and partially because the commutator brushes rub on the slotted commutator. Inside the grinding chamber there is a rotating metal turntable onto which the food waste drops. Two swiveling and sometimes also two fixed metal impellers and mounted on top of the plate near the edge then fling the food waste against the grind ring repeatedly. Sharp cutting edges in the grind ring break down the waste until it is small enough to pass through openings in the ring, and sometimes it goes through a third stage where an Undercutter Disk further chops the food up, whereupon it is flushed down the drain. Usually, there is a partial rubber closure, known as a splashguard, on the top of the disposal unit to prevent food waste from flying back up out of the grinding chamber. It may also be used to attenuate noise from the grinding chamber for quieter operation. There are two main types of garbage disposers—continuous feed and batch feed. Continuous feed models are used by feeding in waste after being started and are more common. Batch feed units are used by placing waste inside the unit before being started. These types of units are started by placing a specially designed cover over the opening. Some covers manipulate a mechanical switch while others allow magnets in the cover to align with magnets in the unit. Small slits in the cover allow water to flow through. Batch feed models are considered safer, since the top of the disposal is covered during operation, preventing foreign objects from falling in. 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. Especially hard objects accidentally or deliberately introduced, such as metal cutlery, can damage the waste disposal unit and become damaged themselves, although recent advances, such as swivel impellers, have been made to minimize such damage. Some higher-end units have an automatic reversing jam clearing feature. 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 early sixties, many disposal units have utilized swivel impellers which make reversing unnecessary. Some other kinds of garbage disposal units are powered by water pressure, rather than electricity. Instead of the turntable and grind ring described above, this alternative design 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.


Environmental impact

Kitchen waste disposal units increase the load of organic carbon that reaches the water treatment plant, which in turn increases the consumption of oxygen. Metcalf and Eddy quantified this impact as of biochemical oxygen demand per person per day where disposers are used. An Australian study that compared in-sink food processing to composting alternatives via a
life-cycle assessment Life cycle assessment or LCA (also known as life cycle analysis) is a methodology for assessing environmental impacts associated with all the stages of the Product lifecycle, life cycle of a commercial product, Process lifecycle, process, or ...
found that while the in-sink disposer performed well with respect to climate change, acidification, and energy usage, it did contribute to
eutrophication Eutrophication is the process by which an entire body of water, or parts of it, becomes progressively enriched with minerals and nutrients, particularly nitrogen and phosphorus. It has also been defined as "nutrient-induced increase in phytopla ...
and toxicity potentials. This may result in higher costs for energy needed to supply oxygen in secondary operations. However, if the waste water treatment is finely controlled, the organic carbon in the food may help to keep the bacterial decomposition running, as carbon may be deficient in that process. This increased carbon serves as an inexpensive and continuous source of carbon necessary for biologic nutrient removal. One result is larger amounts of solid residue from the waste-water treatment process. According to a study at the
East Bay Municipal Utility District East Bay Municipal Utility District (EBMUD), colloquially referred to as "East Bay Mud", is a public utility district which provides water and sewage treatment services for an area of approximately in the eastern side of the San Francisco Bay.S ...
's wastewater treatment plant funded by the EPA, food waste produces three times the biogas as compared to municipal sewage sludge. The value of the biogas produced from anaerobic digestion of food waste appears to exceed the cost of processing the food waste and disposing of the residual biosolids (based on a LAX Airport proposal to divert 8,000 tons/year of bulk food waste).Hernanadez, Gerald L., Kenneth R. Redd, Wendy A. Wert, An Min Liu, and Tim Haug. "Hyperion Advanced Digestion Pilot Program". In a study at the
Hyperion sewage treatment plant The Hyperion Water Reclamation Plant is a sewage treatment plant in southwest Los Angeles, California, next to Dockweiler State Beach on Santa Monica Bay. The plant is the largest sewage treatment facility in the Los Angeles Metropolitan Area an ...
in Los Angeles, disposer use showed minimal to no impact on the total biosolids byproduct from sewage treatment and similarly minimal impact on handling processes as the high volatile solids destruction (VSD) from food waste yield a minimum amount of solids in residue. Power usage is typically 500–1,500 W, comparable to an electric
iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in f ...
, but only for a very short time, totaling approximately 3–4 kWh of electricity per household per year. Daily water usage varies, but is typically of water per person per day, comparable to an additional
toilet A toilet is a piece of sanitary hardware that collects human urine and feces, and sometimes toilet paper, usually for disposal. Flush toilets use water, while dry or non-flush toilets do not. They can be designed for a sitting position popu ...
flush. One survey of these food processing units found a slight increase in household water use.Karlberg, Tina and Erick Norin. VA-Forsk Report, 1999-9. "Food Waste Disposers – Effects on Wastewater Treatment Plants. A Study from the Town of Surahammar".


References

{{Authority control American inventions Home appliances Waste treatment technology Products introduced in 1935 Food waste 20th-century inventions