What is a Grease trap
A grease trap, also known as a grease interceptor, is a plumbing device designed to capture and retain fats, oils, and grease (FOG) from kitchen wastewater before it enters the main drainage system. These substances, when allowed to enter sewers, solidify and accumulate, leading to blockages, odours, sewer overflows, and expensive maintenance operations. Grease traps are essential components in commercial kitchens, particularly in restaurants, hotels, catering facilities, and food processing plants.
Grease traps function by slowing the flow of wastewater, allowing lighter FOG substances to float to the surface, while solids settle to the bottom. The cleaner water in the middle layer is then allowed to pass through to the drainage system.
Why Grease Traps Are Needed
When fats, oils, and grease are washed down kitchen drains, they may initially appear harmless in liquid form. However, as they cool and mix with other debris, they solidify and adhere to the interior of pipes, significantly reducing flow capacity. Over time, this leads to:
- Blocked pipes and drains
- Sewer backups and overflows (known as fatbergs in large-scale systems)
- Nuisance odours and hygiene issues
- Increased municipal maintenance costs
- Environmental pollution and health risks
Grease traps prevent this by intercepting FOG at the source, significantly reducing its impact on downstream infrastructure.
How a Grease Trap Works
Grease traps operate based on the physical properties of FOG — specifically, that fats and oils are less dense than water and do not mix with it. A typical grease trap functions as follows:
- Wastewater enters the trap from a kitchen sink or dishwasher.
- As the flow slows down in the chamber, grease and oils rise to the top, and solids settle at the bottom.
- The clearer middle layer of water exits the trap and continues to the foul water drainage system.
- Accumulated FOG and solids are periodically removed by manual cleaning or professional pumping services.
Grease traps can be installed under sinks (small-scale, passive traps) or outside the building as larger in-ground interceptors, depending on the volume of wastewater being handled.
Types of Grease Traps
There are several types of grease traps, each suited to different applications:
1. Passive Grease Traps (Hydromechanical)
- Typically installed under sinks or inside kitchens
- Compact and relatively low-cost
- Require frequent manual cleaning
- Best for small to medium food outlets
2. Gravity Grease Interceptors (GGIs)
- Larger systems installed externally or underground
- Rely on retention time and gravity separation
- Handle higher volumes of effluent
- Require scheduled pumping and maintenance
3. Automatic Grease Removal Units (AGRUs)
- Mechanised systems that separate and remove grease continuously
- Include skimmers and heaters to liquefy and collect grease in an external container
- Reduce manual cleaning and improve hygiene
- Common in high-output commercial kitchens
Legal and Regulatory Requirements
In many jurisdictions, grease traps are legally required in commercial food establishments. In the UK, for example:
- Water authorities may mandate grease traps under trade effluent agreements.
- Building Regulations (Part H) and Environmental Protection Acts apply where discharges could pollute public sewers.
- Food hygiene regulations and local environmental health officers may inspect and enforce grease management practices.
- Businesses may be held liable for damage or blockages caused by unregulated grease discharge.
Failure to install or maintain a grease trap can result in fines, enforcement notices, or even temporary closure of the premises.
Installation Considerations
Grease trap installation must be tailored to the size and nature of the kitchen operation. Key factors include:
- Flow rate: The unit must be sized according to the volume of wastewater produced.
- Location: Under-sink units must be easily accessible for cleaning; external traps require safe access for pump trucks.
- Compliance: Systems must meet local water authority and environmental standards.
- Accessibility: Units should have removable covers and enough working space for regular inspection and servicing.
Consultation with qualified drainage engineers or environmental consultants is recommended during planning.
Maintenance and Best Practices
Effective grease management is not just about installing a trap — ongoing maintenance is critical. Best practices include:
- Routine cleaning: Frequency depends on kitchen output; under-sink units may need weekly cleaning, while larger interceptors require monthly or quarterly servicing.
- Record keeping: Many authorities require logs of maintenance, cleaning schedules, and waste disposal manifests.
- Proper food waste disposal: Minimising solids entering the system helps trap performance.
- Employee training: Kitchen staff should be trained to understand grease disposal protocols and avoid flushing oils down drains.
Failing to maintain a grease trap reduces its efficiency and can lead to unpleasant odours, overflows, and enforcement action.
Environmental and Operational Benefits
Beyond regulatory compliance, grease traps contribute to broader sustainability and operational goals:
- Reduce risk of costly emergency drain unblocking
- Extend the lifespan of drainage infrastructure
- Improve overall kitchen hygiene and working conditions
- Support local water quality and pollution reduction
- Enable recycling of collected grease into biofuels or industrial lubricants
Conclusion
A grease trap is a vital component of any commercial kitchen’s drainage infrastructure. By capturing fats, oils, and grease at the source, it prevents costly blockages, environmental damage, and operational downtime. Whether installed under a sink or outside as part of a larger interceptor system, grease traps must be correctly sized, legally compliant, and well-maintained. For restaurant owners, facility managers, and drainage professionals, understanding the function, requirements, and maintenance of grease traps is essential to efficient, responsible, and regulation-compliant kitchen operation.