Kitchen Fixtures and Grease Interceptors; Does It Matter?

March 04, 2014

Some plumbing codes have exacerbated FOG related pretreatment problems by incorporating vague language regarding which fixtures should be routed through an interceptor.  Extensive field inspections have proven that FOG is being introduced through every fixture in the kitchen at one point or another.

For some reason not everyone thinks that floor drains or floor sinks need to be routed to an interceptor.  Yet spills like the one pictured here are very common.  We would advise that the kitchen staff isolate a spill like this and use absorbent materials to clean it up carefully.  Yet when it gets busy its more likely that someone with a mop and bucket will rush to the area and "do their best" to get it mopped up or at least liquid enough to squeegee into a nearby floor drain or floor sink.  

We know that dish ware that ends up in a multi-compartment sink is going to produce a significant amount of FOG, but fixtures such as bar sinks get over looked. Yet some common sources of FOG are cappuccino, cafe' breva, cafe' macchiato, cafe' latte, cafe' mocha, frappuccino, hot chocolate, iced cafe's with milk or cream, milk shakes, mixed alcoholic beverages with milk or cream such as white russian, irish coffee, kahlua and cream and so on.  The point being that milk fat is very common and found in many bar drinks where associated glass ware is typically also rinsed and washed.

The best way to prevent a restaurant from discharging FOG to the collection system is to connect all of the following fixtures to a properly sized, installed and maintained grease interceptor:

  • sinks used for washing pots, pans, dishes, cutlery, kitchen utensils, including pre-rinse sinks
  • drains serving self-cleaning exhaust hoods installed over commercial cooking equipment
  • drains serving commercial cooking equipment that discharges oil and grease (i.e. woks, soup kettles, tilt kettles, etc.)
  • drains serving garbage compactors used to compact waste that may contain, or be contaminated with food waste
  • floor drains
  • floor sinks
  • mop sinks

There are two remaining fixtures which should be carefully considered:

  • Dishwasher discharge is a high-temperature mixture of FOG, solids, water and surfactants from excess detergent.  Testing has shown that higher temperatures actually assist in separation performance.  However, interceptors are designed to separate free floating FOG not FOG that has been emulsified by surfactants.  Some jurisdictions believe that it is better to route the dishwasher through the grease interceptor and hope that excess surfactants do not emulsify previously captured FOG, rather than guarantee that the FOG and solids in the dishwasher effluent are delivered directly to the collection system by not routing it through the grease interceptor.
  • Many FSEs scrape dirty dishes into their food waste disposal unit increasing FOG-laden solids that can be discharged to the collection system.  This is a good reason to route these fixtures to a grease interceptor.  However, extra solids loading from a food waste disposal unit can be problematic. To help prevent the interceptor from prematurely filling up with food waste, jurisdictions can require a solids interceptor after a food waste disposal unit or, ultimately, consider eliminating food waste disposal units altogether to improve interceptor performance and reduce the amount of total suspended solids (TSS) entering the collection system.


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