How do grease traps work? A guide to fat, oil, and grease management

Fat and oil might be essential ingredients in commercial kitchens, but they can wreak havoc on drainage systems if not managed correctly. In this blog post, we explore the pressing question for many restaurant managers across the UK who are looking to prevent blockages and environmental damage, ‘how do grease traps work?’.

We will explore grease traps’ function and the crucial role they play in sustainable fat, oil and grease (FOGs) management as well as sharing how Turtle Enviro can support the food and beverage sector with leading solutions.

1. How do grease traps work?

Grease traps, in continuous use since the late 19th century, stand as essential filtration systems within commercial kitchens. Their fundamental purpose is to intercept fats, oils, greases (FOGs) and even starches from wastewater before these problematic substances can enter and damage the delicate sewer system.

These devices, typically constructed from robust materials such as plastic, stainless steel, galvanised steel or fibreglass, can be installed in various configurations. For example, some grease traps can be installed discreetly under a sink, integrated into the kitchen floor, as a standalone unit, or as below-ground plastic grease traps.

At the core of a grease trap’s operation are its inlet and outlet pipes. The trap itself is strategically positioned between the wastewater source (like a sink) and the discharge pipe leading to the external drainage system. When the wastewater containing FOGs enters the trap, natural separation begins.

The principle relies on the differing densities of FOGs and water. FOGs are approximately 70-80% lighter than water and will float on the surface of the water. Simultaneously, any denser solids that have been washed down the sink will settle to the bottom (it is important that excessive solid material such as unfinished food and thick sauces are scraped into a waste bin before dishes are rinsed). The dual separation of FOGs from water significantly reduces the potential for blockages further down the line.

This process is primarily achieved through the strategic placement of baffles within the unit, which prevent the wastewater from flowing directly through. These baffles create the following distinct chambers:

• Inlet chamber: This initial chamber forces the incoming wastewater downwards and significantly slows its flow rate. This reduction in velocity is crucial for allowing the separation process to begin effectively.
• Settlement chamber: As the water settles, the lighter FOGs particles naturally rise to the surface, forming a distinct layer. Any heavier solids present in the wastewater sink to the bottom of this chamber.
• Outlet chamber: Located to collect the relatively de-greased water from below the FOGs layer and above the settled solids, this chamber ensures that only treated water is discharged into the normal sewage system.

For smaller units, often installed under sinks, these are typically known as hydromechanical grease traps. They frequently incorporate vented flow control devices to regulate the volume of wastewater entering the unit, while also introducing air to accelerate the FOGs separation process.

Larger, underground units, referred to as passive or gravity grease separators, capitalise on their greater volume to hold larger quantities of wastewater for longer periods. This extended “retention time” allows gravity alone to perform the necessary FOGs separation, negating the need for active flow control or aeration. The FOGs, being lighter, floats to the surface, where it is effectively trapped, while the cooled, de-greased water continues its journey.

2. What is the purpose of a grease trap?

The most immediate benefit is preventing FOGs from solidifying within drainage pipes. Without a grease trap, congealed FOGs can cling to pipe walls, accumulating over time and leading to severe blockages. These blockages can cause wastewater back-ups, foul odours and expensive emergency plumbing repairs.

Beyond individual premises, grease traps safeguard the integrity of the public sewer network. Large-scale FOGs accumulation in municipal sewers can lead to fatbergs – enormous masses of congealed fat, wet wipes and other debris that cause significant disruptions, environmental pollution, and costly remediation efforts for water authorities.

FOGs can disrupt the biological processes at wastewater treatment plants, making it harder to treat effluent effectively. FOGs can even contribute to pollution of natural water bodies.

3. What is the legislation surrounding grease traps?

A key piece of legislation is The Building Regulations 2000, Part H (Drainage & Waste Disposal). This regulation mandates that drainage systems serving commercial hot food premises must incorporate a grease separator.

Section 111 of the Water Industry Act 1991 makes it a criminal offence to discharge any substance into the public sewers that could impede the free flow of wastewater. This directly includes FOGs. If a water company incurs costs due to FOGs issues, for example removing blockages, cleaning sewers or addressing pollution incidents, they have the legal right to recover these expenses.

The Environmental Protection Act 1990 outlines a ‘Duty of Care’ for all commercial premises regarding waste disposal, including waste cooking oils and fat. This means ensuring all waste is managed correctly from its point of production to its final disposal.

Moreover, the local authority’s environmental health department addresses complaints of ‘statutory nuisance’, which can include unpleasant smells and effluents. If a statutory nuisance linked to FOGs is identified, the local authority is empowered to issue an abatement notice.

4. Which industries are required to use a grease trap?

The focus is primarily on any establishment that prepares or serves food on a commercial scale.

This includes, but is not limited to:

• Restaurants and cafes: From fine dining establishments to local takeaways, all food service businesses are significant producers of FOGs.
• Hotels and guesthouses: Commercial kitchens within hospitality venues fall under these regulations.
• Pubs and bars (with food service): If a pub offers hot food, a grease trap is essential.
• Schools, hospital and care homes: Institutional kitchens preparing meals for a large number of people also require grease management.
• Food manufacturers and processors: Facilities involved in food production where FOGs is a byproduct of their processes.
• Bakeries and delis: Even establishments primarily dealing with baked goods can generate enough FOGs to warrant a trap.

5. How do I maintain a grease trap once installed?

While grease traps are incredibly effective, regular maintenance and cleaning are essential to ensure they continue to function optimally.

Regardless of the type of grease trap your establishment opts for, a critical maintenance aspect is its need for regular emptying. An uncleaned trap will eventually become overloaded with accumulated FOGs and solids, leading to blockages and rendering it ineffective. Larger separators might offer a month or two of operational use before requiring pumping, potentially extended by the addition of biological grease treatment fluids. Smaller units, however, often require daily emptying, though some advanced models feature integrated waste receptacles with automatic removal features, prolonging the intervals between manual cleanings.

Ultimately, a grease trap must be emptied when the accumulated sludge and FOGs reach approximately 25% of the tank’s level. For larger, passive traps, the services of a professional are often sought at regular intervals to ensure thorough cleaning and optimal performance.

Without regular emptying, the trap will eventually overflow, sending untreated FOGs into the drainage system or causing back-ups into the kitchen.

Regular maintenance ensures the following:

• Continued functionality: A full grease trap cannot perform its function effectively. The FOGs layer can become so thick that it prevents proper separation, allowing grease to escape into the sewer.
• Reduced odours: Stagnant FOGs and decomposing food waste within a grease trap can produce highly unpleasant odours, impacting the kitchen environment and potentially deterring customers. Regular cleaning removes these odour sources.
• Extended product lifespan: Proper maintenance prevents the build-up of corrosive substances and excessive strain on the trap’s components, extending its operational lifespan.
• Ongoing compliance: Water authorities will often inspect businesses to ensure they are meeting their trade effluent consent conditions. Demonstrating a robust maintenance schedule for your grease trap is key.
• Cost savings: Professional cleaning is considerably less than the expenses incurred from severe blockages, emergency repairs, fines or business downtime due to sewer issues.

The frequency of cleaning depends on the size of the grease trap, the volume of wastewater generated, and the amount of FOGs produced. High-volume kitchens or those producing a lot of fried food will require more frequent emptying.

How Turtle Enviro can help

For businesses seeking robust and compliant grease management solutions, we offer a comprehensive range of grease traps designed to meet various commercial kitchen needs.

FOGI Underground Grease Interceptor

This product is designed for larger kitchens and restaurants and offers a robust, high-capacity solution that handles significant FOGs loads and ensure your operations run smoothly and compliantly.

The FOGI range offers both vertical and horizontal configurations, each engineered for optimal FOGs separation and long-term performance.

The FOGI grease interceptor chambers arrive pre-assembled and ready for direct underground installation.

GT Grease Traps

The GT Grease Traps range offers a compact option suited for environments that regularly cook with fats and oils and utilise multiple sinks for dish and utensil cleaning.

Specifically engineered for the unique demands of small to medium commercial kitchens, each GT Grease Trap chamber comes pre-assembled.

This range features a smart gravity separation design, optimised by the chambers’ vertical orientation. This vertical structure enhances the natural separation of FOGs from wastewater, allowing fats and oils to rise efficiently to the surface.

The GT Grease Traps are available in a selection of capacities, from 136 litres to 465 litres, allowing you to choose the perfect size to match your kitchen’s specific FOGs output and wastewater volume.

Jumbo Grease Traps

For small to medium-sized kitchens and catering establishments that grapple with a significant output of FOGs, the Jumbo offers a sophisticated solution.

The Jumbo is an underground interceptor that uses the proven principle of gravity separation. Wastewater flow is slowed and cooled, allowing FOGs to float and solids to settle. What makes the Jumbo truly innovative is its patented moulded step within the chamber. This unique feature significantly enhances the settlement and increases the storage capacity for solids and sludge.

Compatible with 110mm EN 1401 pipework, each JGT1A unit boasts a 340-litre capacity. For facilities with high solid loads, such as certain food processing environments, the JGT1 model is recommended, featuring a primary sludge trap with a minimum 100-litre capacity.

Investing in the right grease trap and committing to a rigorous maintenance schedule are fundamental for responsible FOGs management. How do grease traps work, what devices are available and how they help businesses comply with regulations are all essential considerations when dealing with FOGs on a commercial scale.

By opting for a grease trap, commercial kitchens can protect their plumbing, safeguard public infrastructure and contribute to a healthier environment, all while avoiding costly disruptions. Contact the Turtle Enviro team for more information.