What This Requirement Covers
Commercial kitchens produce significant quantities of fats, oils, and grease (FOG) that can block drainage systems and cause pollution. Many water and sewerage companies require grease traps or fat interceptors to be installed on the drainage from commercial kitchens.
Key Requirements
When a Grease Trap Is Required
- Most water companies require grease management for any premises producing food (restaurants, takeaways, hotels, hospitals, schools)
- The requirement is imposed through the trade effluent consent issued by the water company
- Some local authorities also require grease traps as a condition of planning permission or Building Regulations approval
Types of Grease Trap
- Passive (gravity) grease traps: Small units installed under or near sinks; grease floats to the surface and is retained; require regular manual cleaning (weekly or more frequently)
- Automatic grease removal units (GRUs): Electrically powered units that skim grease automatically; require less frequent manual intervention
- Below-ground grease interceptors: Larger chambers installed in the drainage run outside the building; suitable for high-volume kitchens
Design Standards
- Grease traps should comply with BS EN 1825 (Grease separators)
- The trap must be sized for the peak flow rate from the kitchen; undersized traps allow grease to pass through
- The trap must be installed upstream of any connection to the public sewer
- A sample chamber should be provided downstream of the grease trap to allow the water company to test the effluent
Practical Compliance Tips
- Check with the water company for their specific grease management requirements before designing the kitchen drainage
- Size the grease trap correctly; an undersized trap is worse than useless because it gives a false sense of compliance
- Establish a maintenance schedule for the grease trap; failure to empty and clean it regularly causes blockages and odour
- Keep maintenance records as evidence of compliance for the water company and environmental health
- Train kitchen staff not to pour FOG down sinks; provide separate waste collection for used cooking oil
- Consider an automatic GRU for high-volume kitchens; the reduced maintenance burden often justifies the higher initial cost
- Ensure the grease trap is accessible for maintenance; below-ground interceptors need a vehicle access route for tanker emptying