Determining your FOG Maintenance Interval

July 6, 2018 Larissa G.

Determining your FOG Maintenance Interval

Fats, oils and grease (FOG) that go down the drain can create unpleasant odours, clog pipes and can lead to costly sewer back-ups in your business. Don’t get caught in the trap!

It is important to start thinking of your grease interceptor as an integral part of your business’ success. Without consistent, frequent maintenance your grease interceptor can not only fail to do its job but may also accrue fines from the local government when it does.

One of the most important tools to ensure sufficient grease management within a facility is to correctly size, install and maintain a grease interceptor. There are several methods of determining the correct size of the grease interceptor; the most common of which is a calculation of total flow rate. The equation for calculating total rate of flow takes into account the volume of all fixtures, which is connected to the grease interceptor and assigns a drain downtime (usually 1 minute). The result is a calculated flow rate in gallons per minute (GPM) that is used to select a hydromechanical interceptor that is designed for that GPM. While this calculation determines the maximum flow that an interceptor will face, the industry has voiced its concern that it is not enough information to make an accurate selection of equipment.

The argument is that two restaurants with the same number and size of fixtures can produce very different amounts of grease, yet they would have the same sized interceptor if size were based on flow rate.  The end result in this scenario is that one restaurant may have to get their interceptor pumped out more frequently than the other.

The American Society of Plumbing Engineers (ASPE) has recognized a need to create a formulation to account for the differences in grease production of facilities and takes this into account when sizing and selecting an interceptor.

Based on data collected from a 2009 study, average grease production values have been created for 4 categories of grease-producers varying in severity. These values, along with desired and required pump-out frequencies can be used to determine the amount of grease an interceptor needs to hold for a specific job.

The table below shows a more in-depth example of a high volume, high grease producing restaurant with a grease production rate of 0.075lb/meal at 450 meals/day on average and the interceptor maintained every 30 days.

Source: ASPE (American Society of Plumping Engineers) Plumbing & Design Handbook (Volume 4, Chapter 8, 2016)

The second use of this equation is to determine a pump-out frequency for an existing interceptor. In this scenario, let’s assume our flow rate calculation came out to 95GPM and we installed a 100GPM unit that has been third-party tested and certified to hold 1058lbs of grease. Let’s again say we are a high volume, high grease producing restaurant, with a grease production rate is 0.075lb/meal at 450 meals/day. This translates to 33.75lbs of grease per day. If our interceptor can hold 1058lbs, then it will reach capacity every 31.4 days. Thus, your pump-out frequency should be at 30 days.

The Authority Having Jurisdiction (AHJ) (who enforces the city ordinances, State requirements etc.) is often the one who dictates your pump out schedule. However, it is still imperative to get familiar with your interceptor because it is important to know the period between grease clean outs differs for each type. The key takeaway with this is to always rely on experienced licensed professionals. Failure to act in accordance with this can result in mandatory penalties of up to $25000/day/violation.

Keep in mind that oversizing an interceptor to stretch the amount of time between cleanouts may seem like an attractive option, but it will cost you in the long run. Chemical reactions occurring within the grease interceptor reduce the pH of its contents which may result in corrosion of porous material. Further, high levels of hydrogen sulfide have known to be produced from the degradation of grease and food solids – this is where that “rotten-egg” odour associated with the interceptor comes from. Make sure to size your interceptor for a 30-60 day cleaning interval so you don’t incur unfixable problems.



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