What are Grease Traps and How Do They Work?

Nearly half a million tonnes of grease and fat enter the UK sewerage system every year. This poses a significant danger to the environment, as grease can cause blockages and damage to wastewater treatment equipment. To combat this issue, legislation has been implemented to enforce proper management of fats, oils, and grease (FOG) by food service operators.

One effective solution to FOG management is the use of grease traps. With over 100 years of history, grease traps are commonly employed in a variety of environments including restaurants, cafes, takeaways, pubs, hotels, schools, and bakeries. But what exactly are they and how do they work? Let’s find out.

What is a Grease Trap?

A grease trap, also known as a grease interceptor, converter, catcher, grease recovery/management device, or FOG trap, is a receptacle that wastewater containing FOG flows through before entering a drainage system. The purpose of the trap is to intercept or “trap” the FOG while allowing clear water to escape.

How Does a Grease Trap Work?

The functioning of a grease trap is based on the principle that animal fats and vegetable oils (grease) are less dense than water and do not mix with it. When wastewater enters the trap, the flow rate is reduced, which allows the wastewater to cool and separate into three layers. The grease rises to the top and is trapped using a system of baffles, while solids settle at the bottom. The separated clear water escapes through an outlet baffle. Some grease traps also have strainers to collect solid debris, reducing the amount of solids that settle at the bottom.

Over time, solids and grease build-up within the trap, and regular cleaning and pumping are necessary to prevent clogging and back-ups. The frequency of cleaning depends on the amount of wastewater produced and the size of the trap, typically ranging from every 2-4 weeks. However, this time period can be extended to up to 8 weeks by implementing a biological grease treatment fluid, which breaks down FOG and enhances trap performance through a process called “dosing.”

Different types of grease traps include passive hydromechanical (manual), automatic, and gravity traps.

Passive Hydromechanical (Manual) Grease Traps

Passive hydromechanical grease traps are commonly used in smaller establishments due to their low cost and various sizes available. They can be easily installed under sinks, and larger units are available for establishments with higher wastewater production. These traps require manual cleaning on a regular basis and are typically made of plastic or stainless steel.

Automatic Grease Traps

Automatic grease traps, also known as AGRUs (automatic grease removal units), operate similarly to passive traps but have the added capability of automatically re-heating and skimming out the FOG on a programmed schedule. The skimmed FOG is then collected for easy removal and recycling. Automatic traps eliminate the need for manual measurements or checks and are more efficient with lower long-term running and servicing costs.

Gravity Grease Traps

Gravity grease traps are large, in-ground tanks made of concrete, fibreglass, or steel. They function similarly to passive hydromechanical traps but have a higher capacity and are suitable for high-flow applications. These traps require scheduled pumping by a specialist grease management service.

With increased awareness of environmental issues, investing in proper FOG management is not only beneficial but also ensures compliance with future legislation that may become more stringent in the coming years. Take control of your establishment’s FOG management now and future-proof your business.

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