Garbage disposal unit

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A garbage disposal unit installed under a kitchen sink. Waste disposer.JPG
A garbage disposal unit installed under a kitchen sink.

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 between the sink's drain and the trap. The disposal unit shreds food waste into pieces small enough—generally less than 2 mm (0.079 in) in diameter—to pass through plumbing. [1]



The garbage disposal unit was invented in 1927 by John W. Hammes, an architect working in Racine, Wisconsin. [2] He applied for a patent in 1933 that was issued in 1935. [3] His InSinkErator company put his disposer on the market in 1940.[ citation needed ]

Hammes' claim is disputed, as General Electric introduced a garbage disposal unit in 1935, [4] [5] 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 (garbage) into the system. [6] InSinkErator spent considerable effort, and was highly successful in convincing many localities to rescind these prohibitions. [7]

Many localities in the United States prohibited the use of disposers. [8] For many years, garbage disposers were illegal in New York City 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 After a 21-month study with the NYC Department of Environmental Protection, [9] the ban was rescinded in 1997 by local law 1997/071, which amended section 24-518.1, NYC Administrative Code. [10]

In 2008, the city of Raleigh, North Carolina 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of garbage disposers, which also extended to outlying towns sharing the city's municipal sewage system, but rescinded the ban one month later. [11] [12]


In the United States, some 50% of homes had disposal units as of 2009, [13] compared with only 6% in the United Kingdom [14] and 3% in Canada. [15]

In Sweden, some municipalities encourage the installation of disposers in order to increase the production of biogas. [16] Some local authorities in Britain subsidize the purchase of garbage disposal units in order to reduce the amount of waste going to landfill. [17]


Food scraps range from 10% to 20% of household waste, [18] 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 facilities, the high water-content of food scraps means that their heating and burning consumes more energy than it generates; buried in landfills, food scraps decompose and generate methane gas, a greenhouse gas that contributes to climate change. [19]

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), with advanced facilities also capturing methane for energy production. [20] [21]


The parts of a garbage disposal Garbage disposal innards.png
The parts of a garbage disposal
Top view in the sink. The splash guard is visible. In-Sink-Erator.jpg
Top view in the sink. The splash guard is visible.
A modern disposal unit InSinkEratorEvolution.jpg
A modern disposal unit

A high-torque, insulated electric motor, usually rated at 250–750 W (13–1 hp) [22] for a domestic unit, spins a circular turntable mounted horizontally above it. Induction motors rotate at 1,400–2,800 rpm 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 motors, 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. [23] [24]

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. [25] 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.[ citation needed ]

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. [26]

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. [27] 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.[ citation needed ]

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. [28] Metcalf and Eddy quantified this impact as 0.04 pound of biochemical oxygen demand per person per day where disposers are used. [29] An Australian study that compared in-sink food processing to composting alternatives via a life-cycle assessment found that while the in-sink disposer performed well with respect to climate change, acidification, and energy usage, it did contribute to eutrophication and toxicity potentials. [30]

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. [31]

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's wastewater treatment plant funded by the EPA, food waste produces three times the biogas as compared to municipal sewage sludge. [32] 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). [33]

In a study at the Hyperion sewage treatment plant 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. [33]

Power usage is typically 500–1,500 W, comparable to an electric iron, but only for a very short time, totaling approximately 3–4 kWh of electricity per household per year. [34] Daily water usage varies, but is typically 1 US gallon (3.8 l) of water per person per day, [35] comparable to an additional toilet flush. [36] One survey of these food processing units found a slight increase in household water use. [37]

Related Research Articles

Compost Mixture used to improve soil fertility

Compost is a mixture of ingredients used to fertilize and improve the soil. It is commonly prepared by decomposing plant and food waste and recycling organic materials. The resulting mixture is rich in plant nutrients and beneficial organisms, such as worms and fungal mycelium. Compost improves soil fertility in gardens, landscaping, horticulture, urban agriculture, and organic farming, reducing dependency on commercial chemical fertilizers. The benefits of compost include providing nutrients to crops as fertilizer, acting as a soil conditioner, increasing the humus or humic acid contents of the soil, and introducing beneficial colonies of microbes that help to suppress pathogens in the soil.

Sewage sludge Semi-solid material that is produced as a by-product during sewage treatment

Sewage sludge is the residual, semi-solid material that is produced as a by-product during sewage treatment of industrial or municipal wastewater. The term "septage" also refers to sludge from simple wastewater treatment but is connected to simple on-site sanitation systems, such as septic tanks.

Sanitation Public health conditions related to clean water and proper excreta and sewage disposal

Sanitation refers to public health conditions related to clean drinking water and treatment and disposal of human excreta and sewage. Preventing human contact with feces is part of sanitation, as is hand washing with soap. Sanitation systems aim to protect human health by providing a clean environment that will stop the transmission of disease, especially through the fecal–oral route. For example, diarrhea, a main cause of malnutrition and stunted growth in children, can be reduced through adequate sanitation. There are many other diseases which are easily transmitted in communities that have low levels of sanitation, such as ascariasis, cholera, hepatitis, polio, schistosomiasis, and trachoma, to name just a few.

Waste management Activities and actions required to manage waste from its source to its final disposal

Waste management includes the processes and actions required to manage waste from its inception to its final disposal. This includes the collection, transport, treatment and disposal of waste, together with monitoring and regulation of the waste management process and waste-related laws, technologies, economic mechanisms.

Sanitary sewer Underground pipe for transporting sewage

A sanitary sewer is an underground pipe or tunnel system for transporting sewage from houses and commercial buildings to a sewage treatment plant or disposal. Sanitary sewers are a type of gravity sewer and are part of an overall system called a "sewage system" or sewerage. Sanitary sewers serving industrial areas may also carry industrial wastewater. In municipalities served by sanitary sewers, separate storm drains may convey surface runoff directly to surface waters. An advantage of sanitary sewer systems is that they avoid combined sewer overflows. Sanitary sewers are typically much smaller in diameter than combined sewers which also transport urban runoff. Backups of raw sewage can occur if excessive stormwater inflow or groundwater infiltration occurs due to leaking joints, defective pipes etc. in aging infrastructure.

Wastewater treatment Converting wastewater into an effluent for return to the water cycle

Wastewater treatment is a process used to remove contaminants from wastewater and convert it into an effluent that can be returned to the water cycle. Once returned to the water cycle, the effluent creates an acceptable impact on the environment or is reused for various purposes. The treatment process takes place in a wastewater treatment plant. There are several kinds of wastewater which are treated at the appropriate type of wastewater treatment plant. For domestic wastewater, the treatment plant is called a sewage treatment plant. For industrial wastewater, treatment either takes place in a separate industrial wastewater treatment plant, or in a sewage treatment plant. Further types of wastewater treatment plants include agricultural wastewater treatment plants and leachate treatment plants.

Composting toilet Type of toilet that treats human excreta by a biological process called composting

A composting toilet is a type of dry toilet that treats human waste by a biological process called composting. This process leads to the decomposition of organic matter and turns human waste into compost-like material. Composting is carried out by microorganisms under controlled aerobic conditions. Most composting toilets use no water for flushing and are therefore called "dry toilets".


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 sewage sludge from local wastewater treatment plants. Scientific research over many years has confirmed that these biosolids contain similar nutrients to those in animal manures. Biosolids that are used as fertilizer in farming are usually treated to help to prevent disease-causing pathogens from spreading to the public. Some sewage sludge can not qualify as biosolids due to persistent, bioaccumulative and toxic chemicals, radionuclides, and heavy metals at levels sufficient to contaminate soil and water when applied to land.

InSinkErator American producer of kitchen plumbing equipment

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". It is owned by Emerson Electric.

Industrial wastewater treatment Processes used for treating wastewater that is produced by industries as an undesirable by-product

Industrial wastewater treatment describes the processes used for treating wastewater that is produced by industries as an undesirable by-product. After treatment, the treated industrial wastewater may be reused or released to a sanitary sewer or to a surface water in the environment. Some industrial facilities generate wastewater that can be treated in sewage treatment plants. Most industrial processes, such as petroleum refineries, chemical and petrochemical plants have their own specialized facilities to treat their wastewaters so that the pollutant concentrations in the treated wastewater comply with the regulations regarding disposal of wastewaters into sewers or into rivers, lakes or oceans. This applies to industries that generate wastewater with high concentrations of organic matter, toxic pollutants or nutrients such as ammonia. Some industries install a pre-treatment system to remove some pollutants, and then discharge the partially treated wastewater to the municipal sewer system.

Milorganite Brand of biosolids fertilizer produced by treating sewage sludge

Milorganite is a brand of biosolids fertilizer produced by treating sewage sludge by the Milwaukee Metropolitan Sewerage District. The term is a portmanteau of the term Milwaukee Organic Nitrogen. The sewer system of the District collects municipal wastewater from the Milwaukee metropolitan area. After settling, wastewater is treated with microbes to break down organic matter at the Jones Island sewage treatment plant in Milwaukee, Wisconsin. The byproduct sewage sludge is produced. This is heat-dried with hot air in the range of 900–1,200 °F (482–649 °C), which heats the sewage sludge to at least 176 °F (80 °C) to kill pathogens. The material is then pelletized and marketed throughout the United States under the name Milorganite. The result is recycling of the nitrogen and phosphorus from the waste-stream as fertilizer. The treated wastewater is discharged to Lake Michigan.

Sewage sludge treatment Processes to manage and dispose of sludge during sewage treatment

Sewage sludge treatment describes the processes used to manage and dispose of sewage sludge produced during sewage treatment. Sludge treatment is focused on reducing sludge weight and volume to reduce transportation and disposal costs, and on reducing potential health risks of disposal options. Water removal is the primary means of weight and volume reduction, while pathogen destruction is frequently accomplished through heating during thermophilic digestion, composting, or incineration. The choice of a sludge treatment method depends on the volume of sludge generated, and comparison of treatment costs required for available disposal options. Air-drying and composting may be attractive to rural communities, while limited land availability may make aerobic digestion and mechanical dewatering preferable for cities, and economies of scale may encourage energy recovery alternatives in metropolitan areas.

Vacuum sewer Method of transporting sewage from its source to a sewage treatment plant

A vacuum sewer or pneumatic sewer system is a method of transporting sewage from its source to a sewage treatment plant. It maintains a partial vacuum, with an air pressure below atmospheric pressure inside the pipe network and vacuum station collection vessel. Valves open and reseal automatically when the system is used, so differential pressure can be maintained without expending much energy pumping. A single central vacuum station can collect the wastewater of several thousand individual homes, depending on terrain and the local situation.

Grease trap Trap designed to intercept most greases and solids before they enter a wastewater disposal system

A grease trap is a plumbing device designed to intercept most greases and solids before they enter a wastewater disposal system. Common wastewater contains small amounts of oils which enter into septic tanks and treatment facilities to form a floating scum layer. This scum layer is very slowly digested and broken down by microorganisms in the anaerobic digestion process. Large amounts of oil from food preparation in restaurants can overwhelm a septic tank or treatment facility, causing the release of untreated sewage into the environment. High-viscosity fats and cooking grease such as lard solidify when cooled, and can combine with other disposed solids to block drain pipes.

Sewage treatment Process of removing contaminants from municipal wastewater

Sewage treatment is a type of wastewater treatment which aims to remove contaminants from sewage to produce an effluent that is suitable for discharge to the surrounding environment or an intended reuse application, thereby preventing water pollution from raw sewage discharges. Sewage contains wastewater from households and businesses and possibly pre-treated industrial wastewater. There are a high number of sewage treatment processes to choose from. These can range from decentralized systems to large centralized systems involving a network of pipes and pump stations which convey the sewage to a treatment plant. For cities that have a combined sewer, the sewers will also carry urban runoff (stormwater) to the sewage treatment plant. Sewage treatment often involves two main stages, called primary and secondary treatment, while advanced treatment also incorporates a tertiary treatment stage with polishing processes and nutrient removal. Secondary treatment can reduce organic matter from sewage,  using aerobic or anaerobic biological processes.

Sewage Wastewater that is produced by a community of people

Sewage is a type of wastewater that is produced by a community of people. It is typically transported through a sewer system. Sewage consists of wastewater discharged from residences and from commercial, institutional and public facilities that exist in the locality. Sub-types of sewage are greywater and blackwater. Sewage also contains soaps and detergents. Food waste may be present from dishwashing, and food quantities may be increased where garbage disposal units are used. In regions where toilet paper is used rather than bidets, that paper is also added to the sewage. Sewage contains macro-pollutants and micro-pollutants, and may also incorporate some municipal solid waste and pollutants from industrial wastewater.

Effluent sewer

Effluent sewer systems, also called septic tank effluent gravity (STEG) or solids-free sewer (SFS) systems, have septic tanks that collect sewage from residences and businesses, and the liquid fraction of sewage that comes out of the tank is conveyed to a downstream receiving body such as either a centralized sewage treatment plant or a distributed treatment system for further treatment or disposal away from the community generating the sewage. Most of the solids are removed by the interceptor tanks, so the treatment plant can be much smaller than a typical plant and any pumping for the supernatant can be simpler without grinders.

Thermal hydrolysis

Thermal hydrolysis is a process used for treating industrial waste, municipal solid waste and sewage sludge.

Reuse of human excreta Safe, beneficial use of human excreta mainly in agriculture (after treatment)

Reuse of human excreta is the safe, beneficial use of treated human excreta after applying suitable treatment steps and risk management approaches that are customized for the intended reuse application. Beneficial uses of the treated excreta may focus on using the plant-available nutrients that are contained in the treated excreta. They may also make use of the organic matter and energy contained in the excreta. To a lesser extent, reuse of the excreta's water content might also take place, although this is better known as water reclamation from municipal wastewater. The intended reuse applications for the nutrient content may include: soil conditioner or fertilizer in agriculture or horticultural activities. Other reuse applications, which focus more on the organic matter content of the excreta, include use as a fuel source or as an energy source in the form of biogas.

Waste management in South Korea

Waste management in South Korea involves waste generation reduction and ensuring maximum recycling of the waste. This includes the appropriate treatment, transport, and disposal of the collected waste. South Korea's Waste Management Law was established in 1986, replacing the Environmental Protection Law (1963) and the Filth and Cleaning Law (1973). This new law aimed to reduce general waste under the waste hierarchy in South Korea. This Waste Management Law imposed a volume-based waste fee system, effective for waste produced by both household and industrial activities.


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