Every so often, I like to assign homework that gets the brain thinking. Last week, I asked the question, "What is the state limit of FOGs in the sanitary waste?"

The e-mail between the students was hot and heavy. What are FOGs? The question asked about the limits, but the students had no idea what FOGs were.

The question was not intended to stump the students. I just got carried away with the alphabet soup we use in the trade. If you have ever installed a restaurant or commercial kitchen, you have probably heard of FOG. If not, you probably don't have a clue as to what it means.

FOG is not a weather condition that reduces visibility to nothing. FOG stands for fat, oil and grease. It is what we see discharging to the drain in a commercial kitchen. The fats, oils and greases are so nasty in fouling up sewage treatment plants that the states and federal government regulate the amount of FOGs that can discharge to the public sewer system.

Of course, the primary means of preventing FOGs from passing into the public sewer is by the proper installation of a grease interceptor. The key word is "proper." Within the past 10 years, the requirements for grease interceptors have changed. Most of the plumbing codes have changed, as well.

One of the primary concerns was that grease interceptors were not intercepting the grease. High amounts of FOGs were detected in the public sewer. There was a very good answer to this -- we were allowing the majority of the grease to bypass the grease interceptor. Not only were we allowing it to bypass, most of the plumbing codes in the country required this type of installation.

You may be asking, "What do you mean?" If you ever sit and watch the operation of a commercial kitchen during heavy business hours, you will find that the majority of grease in the restaurant is first washed down into the food waste grinder. The second largest amount of grease passes through the dishwasher discharge.

The change in the plumbing codes now permits a food waste grinder and a dishwasher to discharge to a grease interceptor. Before you can connect a food waste grinder to a grease interceptor, the manufacturer of the grease interceptor must recognize such a design. All of the manufacturers that I checked with require a solids interceptor to be installed with the grease interceptor. This is to reduce the amount of solids accumulating in the grease interceptor.

Flow Control

The other concern with the flow control is the vent pipe. While it is called the flow control vent, it really is not a vent at all. The opening is to allow air to enter the flow control. The air in the water helps to break up the grease, allowing for separation in the grease interceptor. Some manufacturers are now equipping their grease interceptors with an air admittance valve. This makes a lot of sense since the AAV will allow air into the flow control, yet it will prevent any odor from emanating into the kitchen area.

One of the problems that has occurred in the past has been the "undersizing" of grease interceptors. Contractors have felt pressure from restaurants that they don't have any grease, hence, they don't need a large grease interceptor. When the grease interceptor could not keep up with the flow, the contractor resorted to the removal of the flow control. With the flow control removed, the flow was too fast through the interceptor, allowing the majority of the grease to bypass the interceptor.

So heed the advice of the manufacturers, don't undersize the grease interceptor!

Rather than a simple grease interceptor, I would recommend that you sell your customers on the latest advance, a grease removal device, or GRD. A new standard, ANSI/ASME A112.14.4, regulates these devices.

GRDs will automatically remove the grease from the grease interceptor. The standard requires the grease to be 95 percent water-free or straight grease. The grease can be sold to a grease renderer for a higher price when presented water-free.

With a GRD, a restaurant does not have to worry about scheduling the cleaning of a grease interceptor. Of course, most restaurants think that a grease interceptor only has to be cleaned every six months. Then they wonder why they are having problems with the grease.

The biggest problem that owners have with a GRD is the initial price. But, in the long run, a GRD pays for itself. With a GRD, all the restaurant needs to do is periodically replace the jar that collects the clean grease that is removed from the interceptor.

Whether it is a plain grease interceptor or a GRD, be sure that the unit has been rated by PDI. This is the organization that certifies grease interceptors. This assures you that the interceptor will work. It is also the first thing lawyers look for when there is a grease interceptor failure.

As far as location, I like to place a grease interceptor as close as possible to the source of the grease. The further away the grease interceptor, the more likely you are to have problems with the drain.

Oh, getting back to that homework question, the maximum amount of FOGs permitted to discharge to the public sewer is 100 mg/l (often referred to as parts per million). None of the students got the right answer.