Passive Grease Traps vs Mechanical Grease Recovery Units

How passive grease traps work

Passive grease traps work by slowing down the flow of wastewater to allow it to cool and separate into three layers: FOG, solids and water. FOG rises to the top of the grease trap, while solids settle or get collected inside a strainer, depending on the design, and the separated water exits from the outlet.

How mechanical grease recovery units work

On the other hand, mechanical grease traps, also called automatic traps or Grease Recovery Units (GRUs), perform the same function as passive traps but with a few additional features. They too slow down the wastewater flow, but typically have a removable strainer basket to collect solids and use a mechanical method to remove the separated FOG.

Some automatic/mechanical grease traps heat the water and automatically skim out the FOG on a programmed schedule, while others operate without a heating element. The skimmed FOG then gets transferred into a collector bin for easy removal, whereas in passive grease traps, kitchen staff or a maintenance contractor need to regularly maintain the unit by removing the grease build-up from within.

Grease build-up and separation efficiency

There is a direct relationship between the efficiency of a grease trap and the amount of accumulated grease it contains. The more grease there is in the trap, the less space remains for effective separation, which affects its overall performance.

As a result, passive grease traps can become significantly less efficient as grease accumulates and must be manually or mechanically removed. Since mechanical/automatic traps regularly skim and remove FOG, grease accumulation inside the unit is reduced. This helps the machines maintain a consistent level of performance, provided they are correctly sized, cleaned and maintained.

Daily maintenance requirements

Mechanical grease traps have an advantage over passive traps as they offer less hassle in daily grease removal. FOG is deposited into an easy-to-empty container on the side of the trap, which requires considerably less time to empty compared to removing grease from within a passive trap.

Larger passive separators require more installation space and usually do not fit directly under sink bowls, although compact passive models are available. They require clearing out the grease from within the unit by hand or by a specialist contractor, with the frequency depending on the size of the trap and how busy the kitchen is.

Mechanical units still require their collector bins and strainer baskets to be emptied regularly. Cleaning and servicing are also needed to ensure that the automatic grease removal system continues to work properly.

Purchase costs and installation

Mechanical traps can be more expensive than a passive unit and require an electrical supply. On the other hand, passive traps do not require an electrical supply and are typically less expensive to buy.

Mechanical grease traps can typically be installed directly underneath sink bowls, provided there is sufficient space and access for maintenance. Some compact passive traps can also be installed in this position, although larger units require a different arrangement. Nonetheless, the time saved in the daily maintenance of a mechanical unit can make the added expense worthwhile.

Pre-rinse sinks and large wok stations

There are also some circumstances in which smaller passive traps may not be suitable, such as sinks with pre-rinse taps or large wok stations. These can produce a high volume of wastewater and grease, requiring a larger unit or a different grease management solution.

Depending on the installation and local water company requirements, a larger passive trap may be needed. The correct capacity must be assessed for the individual kitchen rather than assuming that a 100–400 litre unit will be suitable in every case.

Grease trap installation and maintenance from Grease Guru

At Grease Guru, we can advise on whether a passive grease separator or mechanical grease recovery unit is the most appropriate solution for your commercial kitchen. Our installation service takes into account the kitchen layout, connected equipment, drainage arrangements and access required for regular maintenance.

Once the equipment is installed, our servicing and maintenance programmes help keep it working efficiently. Whether you are fitting out a new kitchen or replacing an existing grease trap, contact Grease Guru to discuss the right equipment and ongoing support for your premises.

Protect Your Commercial Kitchen with Planned Grease Trap Maintenance

Regular grease trap maintenance is one of the simplest ways to reduce drainage problems, improve operational efficiency and protect your commercial kitchen.

If you're looking for professional commercial grease trap maintenance anywhere in the UK, Grease Guru can help. Our experienced team provides nationwide grease trap cleaning, servicing and management solutions tailored to the needs of your business.

Frequently asked questions

What is the difference between a passive grease trap and a mechanical grease recovery unit?

Passive grease traps retain the separated FOG inside the unit until it is removed by kitchen staff or a maintenance contractor. Mechanical grease recovery units automatically skim or recover the separated FOG and transfer it into a collector bin for easy removal.

Which grease trap is best for a busy commercial kitchen?

Mechanical grease recovery units can offer an advantage in busy kitchens because the regular removal of FOG reduces grease accumulation and makes daily maintenance more straightforward. Nonetheless, the right equipment depends on the wastewater flow, grease output, available space and maintenance requirements of the kitchen.

Do automatic grease traps still need regular maintenance?

Yes. Although automatic grease traps remove FOG into a separate container, kitchen staff still need to empty the collector bin and remove food solids from the strainer basket. The unit also needs regular cleaning and servicing to maintain a consistent level of performance.

Can a grease trap fit underneath a commercial kitchen sink?

Many mechanical grease recovery units and some compact passive traps can be installed directly underneath sink bowls. There must be sufficient space for the equipment and access to empty, clean and service it, while larger passive separators require more installation space.

What size grease trap do I need for a pre-rinse sink or wok station?

Pre-rinse sinks and large wok stations can require greater grease management capacity because of the volume of wastewater and grease they produce. The correct size should be established from the connected equipment, wastewater flow and applicable local water company requirements.

Can Grease Guru replace a passive trap with a mechanical grease recovery unit?

Yes. Grease Guru can assess your existing installation and advise on a suitable replacement. The assessment needs to consider the available space, plumbing, electrical supply and maintenance access before the new equipment is installed.