Full Customer Question:

How do you calculate the correct size of grease trap for a restaurant, hotel, canteen, pub or cafe?


There a number of ways to size and select a grease trap according to EN1825-2:2002 Grease Separators – Part 2: Selection of nominal size, installation, operation and maintenance:
1. Measurement of flow
2. Based on catering equipment
3. Based on type of establishment
4. Special Calculation

All of the methods are complex and time consuming. The good news is that we can do it for you for free! However, in this post we will show you and example of how to do it based on Establishment Type.
The formula is:

This is where is gets complicated!

The Temperature Factor, Density Factor and Detergent and Rinsing Aid are read off tables/graphs:

The Max Wastewater Flow (l/s) Qs requires another calculation!

To this calculation you first need to work out the average flow volume per day from the establishment from the formula and tables below:

So tying it all together and taking the option of a Canteen Kitchen here is a full sample calculation:

  • 1200 Meals/day from 07:00-15:00 (8 hours/day)
  • t = 8 h
  • M = 1200 meals
  • Vm = 5 l (from table)
  • F = 20 (from table)
  • V = 1200/day (M) x 5 l (Vm) = 6000 l/day.
  • QS = 6000 l/day (V) x  20 (F) ÷ 3600 x 8 h (t) = 2.33 l/s
  • ft = 1.0 fd = 1.0 fr = 1.3
  • 2.33 l/s QS x 1.0 (ft) x 1.0 (fd) x 1.3 (fr) = 3.03 l/s
  • Nearest separator: NS 4.0 l/s  (BMS GT04)

The whole process is quite complicated!  Let us do the hard work for you, give us a call on +353 43 3326100 email us or email us on [email protected]

BMS is a quality manufacturer of package products for wastewater and stormwater treatment. BMS started in 1986 and has exported products to over 50 countries around the world.  It is a third generation family business with huge expertise in wastewater and stormwater.
BMS also manufacture a full range of products for surface water and wastewater treatment including our pioneering next generation RBC system the Aerotor, which forms part of our world leading Blivet package sewage treatment plant, a ‘one stop shop’ for all surface water products from design to installation including attenuation, interceptors, holding tanks (incl. chemical resistant), hydrobrakes, rainwater harvesting tanks & vortex silt/oil/debris separators, fully fitted pumping stations, our plug & play vehicle wash water recycling system; the Recyclone and much more.  Please see our enclosed Company & Product Profile for a full summary or View our full product/services catalogue at this link

BMS also can provide a Free Design Service for Sewage Treatment, Pump Stations or Surface Water and a full O&M, Repair, Advice and Testing service for existing installations.  We also can do free CPD Presentations on Sewage Treatment/Surface Water Management at any location.  Let us know when suits.

We would be delighted to discuss any requirements you might have, and we are available to meet you at your convenience.  Please do not hesitate to contact us.