Municipal utilites have to be vigilent about preventing FOG from entering their collections systems. Grease issues cost municipalities millions of dollars every year through replacing or repairing clogged sewer lines, and large amounts of grease can also negatively impact the health of the treatment plant.

To address this FOG issue, some municipalities have implemented regulations requiring mandatory pumping at set intervals (often every 30 to 60 days) for restaurant grease interceptors. These regulations attempt to solve the problem by keeping grease out of the municipal sewage system. If the grease is pumped out of the tank every 30 to 60 days, it can’t go into the sewer system, right? Wrong! What happens on days when the tank isn’t pumped? These types of ordinances fall short of solving the problem because they aren’t taking into account how grease moves into and out of the interceptor tanks.  In order to develop commonsense plans of attack in dealing with grease, you first have to understand the nature of grease, where it’s generated and what happens to it in the wastewater environment.

The greatest source of grease in any municipal sewer system obviously comes from restaurants. Hopefully, the kitchen staff is doing a good job of following best management practices, which include doing a dry wipe-down of all cooking utensils to remove large amounts of grease for disposal in solid waste bins before going into the sink or commercial dishwasher. In reality, however, when things get rushed in the kitchen, it becomes much easier to drop those greasy utensils into the bin of the three-compartment sink filled with hot soapy water. Why? Because it takes more time to physically scrape off grease from utensils and pans than letting the hot (above 85 degrees F) water liquefy it so the utensils are easier to wash, and the grease eventually just goes down the drain when the plug is pulled.

Now, consider that a commercial dishwasher has its final rinse cycle set to 125 degress F or above according to the code set by the local health department, and now you have a recipe for creating a very hot greasy wastewater soup going to the interceptor tank.

The effluent inside the grease interceptor is warmer in the core of the tank (above 85 degrees F), and it’s kept warm because additional hot water is being intermittently added by drainage from sinks and dishwashers. Traditional designs for grease interceptor tanks include a small 4-inch outlet with an inlet about a foot off the floor of the tank. Inside the tank, the hot greasy water is less dense than the cooler water around the perimeter, and so it can be more easily drawn into the small 4-inch downpipe on the tee baffle. From this point, it enters the municipal sewer system, with miles of surface area inside the pipes where the effluent soon becomes much cooler than in the interceptor tank. While the rapid cooldown is better for preventing foodborne illness, it creates a huge problem for cities because once it cools down in sewer pipes, it comes out of the effluent solution and begins to clump and adhere to the sewer pipes, eventually blocking them.

Historically, the most common way to deal with FOG in municipal systems is through regulatory measures — passing ordinances requiring pumping of the interceptors at mandatory intervals. But pumping the interceptor to remove the grease only works if the frequency is such that the interceptor never fills to the point of discharge. Some types of food establishments produce much more grease than others; in order to effectively prevent grease from entering a municipal sewer system, some interceptors would need to be pumped every few days, not weeks. Because of the cost of pumping and dealing with the grease once it’s pumped, it’s not practical or economical to pump interceptor tanks every few days.

To find a much more common sense way to deal with FOG, kitchen protocols and municipal regulations should consider how time, temperature and filtration affect grease:

The first step is always to prevent as much grease as possible from being discharged into the sewer lines in the first place. It’s important to have kitchen staffs follow best management practices as best they can, and to also encourage them not to use degreasers and emulsifiers in their kitchens. (Instead of helping, these types of products actually aggravate the situation.)

Whenever a grease system is initially installed, it’s best to use two smaller interceptor tanks rather than one large tank, or one that is chambered so the effluent has more of a chance to mix cooler perimeter water with that in the warmer core.

Include in the system either a larger-diameter, or better yet, multiple-outlet baffles to slow the velocity of the discharging effluent, which causes grease to more easily come out of solution and clump with other organics in the waste stream; the clumped grease and organics will then fall back into the tank instead of being carried downstream to sewer lines.

Outlet effluent filters with a filtration level of 1/32 of an inch should be used in wastewater systems to retain the grease within the interceptor. It is much more manageable to deal with grease clumped on the effluent filters by setting up a maintenance program to swap out clogged filter cartridges with clean ones as needed, cleaning them, then swapping them out again on the next service call.

Finally, pump the interceptor at shorter intervals when service personnel note that filters are plugging, not at some mandated interval.  

Elected officials can be educated by treatment plant operators who understand how grease acts in the sewer system, then can use their new-found knowledge to write more effective ordinances than ones that mandate pumping at set intervals. If your municipality has such an ordinance, ask a few of your restaurant owners what their cost is for this frequent pumping. It’s expensive, and is a hardship on many small-business owners. However, if restauranteurs are given the option of improving their practices through staff training, installing approved 1/32-inch effluent filters to trap the grease, establishing a service regimen with their pumper or maintenance company, then pumping the tank based on true need than at arbitrary intervals, you will have an effective system for dealing with grease.

Using this system, the restaurant owner is happy, because while he has a bit more expense when the sytem with an effluent filter is first installed, he has fewer expenses each month from mandatory pumping fees, and management of the system with effluent filters is directly related to how much grease the business produces. Utility operators are happy because this method is much more effective in preventing grease from entering the system and damaging plant equipment and clogging municipal sewer lines. Finally, your elected officials are happy, because they’ve used today’s technology and old-fashioned common sense to put in place regulations that are fair and effective in solving their city’s grease problem, with costs to repair their infrastructure steadily dropping. F

About The Author

Theo Terry is the inventor of 19 patented wastewater products and CEO of Bear Onsite LLC. You can contact him to learn more about handling grease, and ways to utilize manifolded filters in grease management at theo.terry@bearonsite.com or 877/653-4583.