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How Often Should Restaurants Perform Professional Grease Trap Cleaning?

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Restaurants and other commercial food establishments need to keep their premises spotlessly clean, both to maintain hygiene standards and their reputation.

Grease trap cleaning is a not so obvious cleaning task, but it is no less vital to ensuring the smooth running of kitchen operations. Regular and effective grease trap cleaning also ensures a food business does not breach waste water regulations, prevents sewer blockages, which cause local flooding, and helps protect the environment.

Food businesses can also support good FOG management practice in their establishments by training kitchen staff, proper waste disposal, and putting up ‘no grease' signposts to warn colleagues not to dispose of fats, oils, and food waste down sinks and drains.

Code of Practice

Food service establishments, including restaurants, pubs, canteens, fast food outlets, and cafes are required to have a properly designed grease trapping equipment installed and commissioned if they create fats, oils, and grease (FOG). Guidelines for this equipment are issued in a code of practice drawn up by Irish Water.

Grease traps allow waste water to flow to the sewage works for treatment while holding back the FOG, which can be collected and disposed of by licensed waste companies at regular intervals.

FOG in wastewater leads to blockages and backups in municipal drains and pipes. Official guidelines also emphasis the need for effective routine maintenance procedures to ensure optimal performance of the grease traps. Food premises need to keep written records of the maintenance procedures required by environmental health officers.

Types of Grease Trap

There are four main types of grease interceptor:

1. Small Hydromechanical Grease Interceptor (HGI)

A hydromechanical grease interceptor is usually installed under a sink. It allows passive oil trapping, and needs regular cleaning (usually every week) in commercial kitchens. Hydromechanical interceptors are least expensive to install. However, grease trap maintenance professionals note that they cost more in the long-run due to the need for more frequent maintenance.

2. Automatic Grease Removal System

This can be a good alternative to the hydromechanical interceptor. The device features an automatic mechanism for removing the grease from the tank, and separating it in a container. These types of grease traps have to meet the same efficiency standards as HGIs. Food establishments must be able to prove they skim FOG effectively.

3. Gravity Grease Interceptors (GGI)

GGIs separate water, solid waste, and FOG through the force of gravity. They are tanks, made from metal, concrete or plastic, that collect waste water, where the separation takes place. FOG floats to the surface, while solids sink to the bottom. The outflow piping system then allows the waste water to flow away into the sewer network or water treatment plant. Gravity grease interceptors need to be pumped out regularly, usually when solids and grease amount to 25% of the content. GGIs are more costly to install, but need less frequent maintenance than HGIs.

4. Maximum Retention HGIs

These devices have become popular in the recent years, especially for restaurants in locations that do not have space for larger conventional grease interceptors, like GGIs. Maximum Retention HGIs are smaller, yet trap more FOG per volume up to 85% of liquid capacity). Also, grease trap maintenance may not have to be as frequent as with some other devices.

The Size of the Grease Trap

As can be seen from the type of grease interceptors already described in this article, the size of the trap depends on a number of factors:

  • The type of grease trap selected
  • Volume of FOG generated by the food preparation process
  • The amount of waste water generated – which depend on how busy the food establishment is
  • Access to, and cost of, grease trap maintenance services

Installing the largest possible grease trap may seem the best option – common volumes for tank-based grease interceptors are 3,000 litres and 5,000 litres. However, if the grease trap is then under-used, the waste water within it may become stagnant, leading to bacteria growth, as well as odor problems.

Grease trap cleaning experts advise installing traps that are more efficient and have the right capacity for the food establishment. For example, it could be more cost-effective in the long-term to install a Maximum Retention Hydromechanical Grease Interceptor because it can hold up to 85% FOG and solid waste, while requiring less frequent maintenance.

Grease traps and tanks that are too small for a food establishment can present a unique set of problems. These include incurring fines by causing pollution incidents if the trap overfills.


Control of fats, oils and grease (FOG) ,

Code of Practice for Wastewater Infrastructure,

Guidelines to Management of Fats, Oils & Grease in Food Service Establishments,

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