What is a grease interceptor and why is it required in a commercial kitchen?

One of the most misunderstood mechanical devises in a restaurant is the grease interceptor. The purpose of a grease interceptor is to remove the oils and fats from your sanitary system before connecting into the city main.  If we didn’t install grease interceptor’s the city mains could become plugged and thus backing up the sanitary system.

All new and old restaurants must comply with GVRD Bylaw #268, there is no grandfathering of existing restaurants.  So you may ask what if we choose not to comply with the bylaw?  Metro Vancouver Sewage Control Manager might choose to take legal or other necessary actions to stop the contravention.  For further information about the bylaw please click on this link: Bylaw #268

In this post I will describe how to calculate the size of your grease interceptor for any restaurant in Vancouver and the Lower Mainland:

1.  First you have to know what type of fixtures should connect to your grease interceptor: kitchen sinks, bar sinks, mop* sinks, dishwashers, glass washers, espresso machines and floor drains* all drain into the grease interceptor.

2.  Do not connect: hand sinks**, ice machines, toilets, lavatories, urinals, condinsate or clear water waste from a drain pan or refrigeration coil into your grease interceptor.

3.  Grease interceptors are sized on the total volume of all the fixtures connected to it.  First measure the inside dimensions of the sink in inches.  Multiply the dimensions together and this will give you the volume in cubic inches.

4.  Take this volume in step 3 and divide the cubic inches by 231.  This will give you GPM (Gallons Per Minute) of that fixture.

5.  Since floor drains don’t have a basin they are given a nominal GPM based on size:  2″ floor drain is 22 GPM, 3″ drain is 37.5 GPM, and a 4″ is 45 gpm

6.  Dishwashers & Glasswashers are sized on their sanitary pumps.  Ask the supplier what the peak sanitary discharge rate is in GPM.

7.  Sum up all the GPM’s  in step 4, 5 and 6.  This total GPM will be the minimum flow rate of your grease interceptor.

Here’s an example:

You are opening a kitchen and you have a single compartment sink, mopsink, dishwasher and 2″ floor drain.  The single compartment sink is 20″x20″x18″, mop sink is 24″x24″x11″, dishwasher manufacture states peak discharge rate is 34gpm.

Solution

  1.  Single compartment sink: 20x20x18/231 = 31.2 gpm
  2. Mop sink: 24x24x11/231 = 27.4 gpm
  3. dishwasher = 34 gpm
  4. 2″ floor drain = 22 gpm
  5. sum up gpm’s = 114.6 gpm

Therefore your grease interceptor needs to have a minimum of 114.6 gpm.  Since grease interceptors are built in nominal sizes you must chose the next size up.  In this case a Watts WD-215 with a peak gpm of 150 will suffice, Click here for Watts website

This sizing method is enforced by the Environmental Protection Branch in accordance with GVRD ByLaw #268-2012.  For more information about calculating the size of a grease interceptor you can contact Natasha Markovic at the EPB: natasha.markovic-mirovic@metrovancouver.org, 604-436-6887.  Always check with the EPB and your Mechanical Engineer before ordering your grease interceptor.

*In some cases mop sinks and floor drains are considered non-simulantous loads.  Thus not adding to the gpm of the interceptor but must be connected to it.

**this may be overturned in the coming months by the GVRD