Grease interceptor

Manhole covers of a Grease Trap outside of a restaurant.

Grease traps (also known as grease interceptors, grease recovery devices and grease converters) are plumbing devices 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. However, very large amounts of oil from food production in kitchens and restaurants can overwhelm the septic tank or treatment facility, causing a release of untreated sewage into the environment. Also, high viscosity fats and cooking greases such as lard solidify when cooled, and can combine with other disposed solids to form blockages in drain pipes.

Grease traps have been used since the Victorian days, although Nathaniel Whiting obtained the first patent for a modern day grease trap in the late 1800s. They are used to reduce the amount of fats, oils and greases (FOGs) that enter the main sewers. Effectively they are boxes within the drain run that flows between the sinks in a kitchen to the sewer system. They only have kitchen waste water flowing through them and are not served by any other drainage system such as toilets. They can be made from a number of different materials; e.g. stainless steel, plastics, concrete & cast iron. They range from 35 litre capacity to 45,000 litres and above capacity. They can be located above ground, below ground, inside the kitchen or outside the building.

Types

There are four primary types of devices. The most common are the types specified by ASME (American Society Of Mechanical Engineers),utilizing baffles, or a proprietary inlet diffuser. The most popular are small point of use units used under three compartment sinks within the kitchen. They restrict flow and remove 85-90% of the incoming FOG. There are also several manufacturers that have engineered outdoor grease interceptors to meet the requirements of the ASME Standards, and to take advantage of the improved performance of hydro-mechanical design. Grease trap sizing is based on the size of the 2 or 3 compartment sink, dishwasher, pot sinks, and mop sinks. The cumulative flow rates of the aforementioned devices, as well as overall grease retention capacity (typically 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 United States. This standard requires that grease interceptors remove a minimum of 90% of the incoming FOGS. It also requires that grease interceptors are third-party tested and certified to compliance with the standard. This third-party testing must be conducted by a recognized and approved third-party testing laboratory.

The second most common type of interceptor is the large in-ground tank, which is usually 750-2000 gallons. These units are constructed of concrete, fiberglass, or steel. By nature of their larger size, they have larger grease and solid storage capacities for high-flow applications such as a restaurant or grocery store. They are commonly called gravity interceptors.

A third system type, known as AGRUs (Automatic Grease removal Units) or GRDs (Grease Recovery Devices), are meant to remove the surface grease automatically when trapped. These units can often be sold as all singing all dancing magic solution. Sizing can often be an issue and in undersized units the heating element liquidises the fat and oil and can allow it to flow straight through the unit. Grease removal is by hydrostatic pressure, motorized skimmer device, or sensor driven automatic draw-off system. They have an internal strainer basket for food particles, an internal heater element, and an external collector box for removal of grease/oil to recycling container. All of these types of devices have to have external power and rely on working heaters and in the mechanical types, timers, motors or skimmers. Care should be taken as suppliers of these units recommend they be installed in the kitchen undersink, this is not an ideal place to put electrical wiring for obvious reasons. Also, should these units develop a fault the whole kitchen can come to a standstill as the waste cannot flow through the unit and instead can buildup and overflow causing flooding. On a standard grease interceptor this would not be a problem, however these devices require an engineer or electrician to resolve, meantime the washing up comes to a standstill. Testing certification for GRD's in North America is ASME A112.14.4. The problem with these tests is they are only tested using lard and water. In a real installation the units are subjected to oil, grease and food particles. So, although the testing shows in a laboratory the unit working, after 6 months insitu in a busy commercial restaurant the test results mean nothing as these units have not been tested long term to cope with waste organic matter.

The fourth type, Grease Converters, Grease Traps, Interceptors, trap grease in a tank similar to a grease interceptor, which is then dosed with a culture of microorganisms to digest the grease, food and oil converting it to water and co2, bio-degradable products which are safely discharged into the drainage system. When used in conjunction with an automatic dosing system, Grease Converters require minimal maintenance, as the grease doesn't require removal, storage or disposal. These units can be installed in the kitchen as they hold no threat to health or safety, hence it makes maintenance simple and prevents problems at source. Major advances in the field of biotechnology is now allowing organisations to employ bacteria in multipal diverse operations. From waste degredation to mining. Biotechnology is being introduced worldwide as one of the fastest growing technologies today and in the field of waste microbiology is the way of the future.

Uses

Restaurant and foodservice kitchens produce a lot of waste grease which is present in the drain lines from the various sinks dishwashers and cooking equipment such as combi ovens and commercial woks. If not removed the grease will congeal within the sewer and cause blockages and back-ups.

In the United States, 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 fit some kind of interceptor device to collect the grease before it enters the sewer. Additionally where FOG is a concern in the local wastewater collection system communities have set up inspection programs to ensure that these grease traps and/or interceptors are being maintained on a routine basis.

Method of operation

A traditional grease trap is not a food disposal unit. Unfinished food must be scraped into the garbage or food recycling bin. Milkshakes, gravy, sauces and food solids must be scraped off the dishes before they enter the sink or dishwasher.

To try to maintain some degree of efficiency there has been a trend to specify larger and larger traps. Unfortunately, providing a large tank for the effluent to stand also means that food waste scraps also have time to settle to the bottom of the tank, further reducing the available volume and adding to the clean out problem. Also, rotting food contained within an interceptor breaks down producing toxic waste (i.e. sulfur gases) - hydrogen sulphide combines with the water present to create sulphuric acid. This attacks mild steel and concrete materials resulting in "rot out". A bigger interceptor is not a better interceptor. Because it will have been in the trap for some time, grease collected in this way will have been contaminated and is unsuitable for further use. This kind of grease is referred to as brown grease.

Biological Certification 3rd party testing

The first Combined Greasetrap and Biological Dosing System was introduced In the UK 20 years ago by Aluline Limited. Many companies try to market alternative dosing products for greasetraps and they usually are a mix of surfactants which do not work and in some cases cause further problems. The only company in UK providing test certificates for grease trap bioremediation systems is Aluline Ltd. The Aluzyme system is tested by the Public Health Laboratories to ascertain the content and ensure no harmful bacteria are present. The Alutrap system is highly effective as well as very simple to maintainain and cost effective.

Disposal of grease

Aluline Ltd provide a training program on prevention at source and to date this is the best method of preventing problems within the drainage system.

There are certain companies trying to market devices that "remove grease and oil" as yellow grease. This is doubtful and care should be taken and independent advice from EA and DEFRA or certification from our UK regulator to ensure against fines or prosecution as ignorance is not an excuse in the eyes of the law, and blocking a main drain can be tried for a criminal offence.

See also

• American Society of Mechanical Engineers (ASME)
• Plumbing and Drainage institute (PDI)
• NERV (Reactor)
• WERF Report - Widely recognized as one of the best studies done on restaurant grease traps