![Grease trap for greywater (5293658840)](https://upload.wikimedia.org/wikipedia/commons/1/18/Grease_trap_for_greywater_%285293658840%29.jpg)
A grease trap (also known as grease interceptor, grease recovery device, grease capsule and grease converter) is a
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 ...
device (a type of
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 ...
) 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
A septic tank is an underground chamber made of concrete, fiberglass, or plastic through which domestic wastewater (sewage) flows for basic sewage treatment. Settling and anaerobic digestion processes reduce solids and organics, but the treatme ...
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
Anaerobic digestion is a sequence of processes by which microorganisms break down biodegradable material in the absence of oxygen. The process is used for industrial or domestic purposes to manage waste or to produce fuels. Much of the ferm ...
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
Lard is a semi-solid white fat product obtained by rendering the fatty tissue of a pig.[Lard]
entry in the o ...
solidify when cooled, and can combine with other disposed solids to block drain pipes.
Grease traps have been used since Victorian days: Nathaniel Whiting obtained the first patent in the late 1800s. The traps reduce the amount of fats, oils, greases, and solids (FOGS) that enter sewers. They consist of boxes within the drain run that flows between the sinks in a kitchen and the sewer system. They have only kitchen waste water flowing through them and do not serve any other drainage system, such as toilets. They can be made from various materials, such as stainless steel, plastics, concrete and cast iron. They range from 35-liter capacity to 45,000 liters and greater. They can be located above ground, below ground, inside the kitchen, or outside the building.
Types
There are three primary types of devices. The most common are those specified by
ASME
The American Society of Mechanical Engineers (ASME) is an American professional association that, in its own words, "promotes the art, science, and practice of multidisciplinary engineering and allied sciences around the globe" via "continuing ...
(American Society Of Mechanical Engineers), utilizing baffles, or a proprietary inlet diffuser.
Grease trap sizing is based on the size of the 2- or 3-compartment sink, dishwasher, pot sinks, and mop sinks. Many manufacturers and vendors offer online sizing tools to make these calculations easy. The cumulative flow rates of these devices, as well as overall grease retention capacity (in pounds or kilograms) are considered. Currently, ASME Standard (ASME A112.14.3) is being adopted by both of the National Model Plumbing Codes that cover most of the US. This standard requires that grease interceptors remove a minimum of 90% of incoming FOGs. It also requires that grease interceptors are third-party tested and certified to 90 days compliance with the standard pumping. This third-party testing must be conducted by a recognized and approved testing laboratory.
Passive grease traps are generally smaller, point-of-use units used under three-compartment sinks or adjacent to dishwashers in kitchens.
Large in-ground tanks, usually , are also passive grease interceptors. These units, made of concrete, fiberglass, or steel, have greater grease and solid storage capacities for high-flow applications such as a
restaurant
A restaurant is a business that prepares and serves food and drinks to customers. Meals are generally served and eaten on the premises, but many restaurants also offer take-out and food delivery services. Restaurants vary greatly in appearan ...
or
hospital
A hospital is a health care institution providing patient treatment with specialized health science and auxiliary healthcare staff and medical equipment. The best-known type of hospital is the general hospital, which typically has an emerge ...
store. They are commonly called gravity interceptors. Interceptors require a retention time of 30 minutes to allow the fats, oils, grease, and food solids to settle in the tank. As more wastewater enters the tank, the grease-free water is pushed out of the tank. The rotting brown grease inside a grease trap or grease interceptor must be pumped out on a scheduled basis. The brown grease is not recycled and goes to landfills. On average of brown grease goes to landfill annually from each restaurant.
Passive grease traps and passive grease interceptors must be emptied and cleaned when 25% full. As the passive devices fill with fats, oils, and grease, they become less productive for grease recovery. A full grease trap does not stop any FOG from entering the sanitary sewer system. The emptied contents or "brown grease" is considered hazardous waste in many jurisdictions.
A third system type, Hydromechanical Grease Interceptors (HGIs), has become more popular in recent years as restaurants open in more nontraditional sites. Often, these sites don't have space for a large concrete grease interceptor. HGIs take up less space and hold more grease as a percent of their liquid capacity — often between 70-85% of their liquid capacity or even higher as in the case of some Trapzilla models. These interceptors are 3rd party certified to meet efficiency standards. Most are made out of durable plastic or fiberglass, lasting much longer than concrete gravity grease interceptors. They are usually lightweight and easy to install without heavy equipment. Most manufacturers test beyond the minimum standard to demonstrate the full capacity of the unit.
Finally, Automatic Grease Removal Devices or recovery units offer an alternative to hydromechanical grease interceptors in kitchens. While their tanks passively intercept grease, they have an automatic, motorized mechanism for removing the grease from the tank and isolating it in a container. These interceptors must meet the same efficiency standards as a passive HGI, but must also meet an additional standard that proves they are capable of skimming the grease effectively.
They are often designed to be installed unobtrusively in a commercial kitchen, in a corner, or under a sink. The upfront cost of these units can be higher, but kitchen staff can handle the minimal maintenance required, avoiding pumping fees. The compact design of these units allows them to fit in tight spaces, and simplifies installation.
Uses
![InGroundGreaseTrap](https://upload.wikimedia.org/wikipedia/commons/6/64/InGroundGreaseTrap.JPG)
Restaurant and food service kitchens produce waste grease which is present in the drain lines from various sinks, dishwashers and cooking equipment such as
combi ovens and commercial
wok
A wok (; Pinyin: ; Cantonese ) is a deep round-bottomed cooking pan from China. It is believed to be derived from the South Asian karahi. It is common in China and similar pans are found in parts of East, South and Southeast Asia, as well as ...
s. Rotisserie ovens have also become big sources of waste grease. If not removed, the grease can clump and cause blockage and back-up in the
sewer.
In the US, sewers back up annually an estimated 400,000 times, and municipal sewer overflows on 40,000 occasions. The EPA has determined that sewer pipe blockages are the leading cause of sewer overflows, and grease is the primary cause of sewer blockages. Even if accumulated FOG does not escalate into blockages and sanitary sewer overflows, it can disrupt wastewater utility operations and increase operations and maintenance requirements.
For these reasons, depending on the country, nearly all municipalities require commercial kitchen operations to use some type of interceptor device to collect grease before it enters sewers. Where FOG is a concern in the local wastewater system, communities have established inspection programs to ensure that these grease traps and/or interceptors are being routinely maintained.
It is estimated 50% of all sewer overflows are caused by grease blockages, with over of raw sewage spills annually.
Method of operation
When the outflow from the kitchen sink enters the grease trap, the solid food particles sink to the bottom, while lighter grease and oil float to the top. The relatively grease-free water is then fed into the normal septic system. The food solids at the bottom and floating oil and grease must be periodically removed in a manner similar to
septic tank
A septic tank is an underground chamber made of concrete, fiberglass, or plastic through which domestic wastewater (sewage) flows for basic sewage treatment. Settling and anaerobic digestion processes reduce solids and organics, but the treatme ...
pumping. A traditional grease trap is not a food disposal unit. Unfinished food must be scraped into the garbage or food recycling bin. Gravy, sauces and food solids must be scraped off dishes before entering the sink or dishwasher.
To maintain some degree of efficiency, there has been a trend to specify larger traps. Unfortunately, providing a large tank for the
effluent
Effluent is wastewater from sewers or industrial outfalls that flows directly into surface waters either untreated or after being treated at a facility. The term has slightly different meanings in certain contexts, and may contain various pollut ...
to stand also means that
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 ...
has time to settle to the bottom of the tank, reducing available volume and adding to clean-out problems. Also, rotting food contained within an interceptor breaks down, producing toxic waste (such as sulfur gases) -
hydrogen sulfide
Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is poisonous, corrosive, and flammable, with trace amounts in ambient atmosphere having a characteristic foul odor of rotten eggs. The unde ...
combines with the water present to create
sulfuric acid
Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular formu ...
. This attacks mild steel and concrete materials, resulting in "rot out", On the other hand, polyethylene has acid-resisting properties. A larger interceptor is not a better interceptor. In most cases, multiple interceptors in series will separate grease much better.
Because it has been in the trap for some time, grease thus collected will be contaminated and is unsuitable for further use. This type of grease is called
brown grease
A grease trap (also known as grease interceptor, grease recovery device, grease capsule and grease converter) is a plumbing device (a type of trap) designed to intercept most greases and solids before they enter a wastewater disposal system. Co ...
.
Brown grease
Waste from passive grease traps and gravity interceptors is called brown grease. Brown grease is rotted food solids in combination with fats, oils, and grease (FOG). Brown grease is pumped from the traps and interceptors by grease pumping trucks. Unlike the collected
yellow grease
Yellow grease, also termed used cooking oil (UCO), used vegetable oil (UVO), recycled vegetable oil, or waste vegetable oil (WVO), is recovered from businesses and industry that use the oil for cooking.
It is used to feed livestock, and to manufa ...
, the majority of brown grease goes to landfill sites. New facilities (2012) and new technology are beginning to allow brown grease to be recycled.
References
External links
* A112.14.3 Grease Interceptors Standard and A112.14.6 FOG (Fats, Oils, & Greases) Disposal Systems Standard,
American Society of Mechanical Engineers
The American Society of Mechanical Engineers (ASME) is an American professional association that, in its own words, "promotes the art, science, and practice of multidisciplinary engineering and allied sciences around the globe" via "continuing ...
(ASME)
{{Authority control
Plumbing
Sewerage infrastructure
Sanitation