How to deal with too much fat, oil and grease in your wet wells

3 October 2017


The best way to deal with the effects of fats, oils, and grease (FOG) in your process is through prevention. FOG that gets washed down drain pipes in homes, food plants, restaurants or any other source is expensive to cope with. Just like the negative effects that plaque has in the arteries of the human circulatory system, FOG has a similar effect on sewer pipes.

When FOG hardens, it can clog the system and back up where it came from or overflow to streets and even natural resources like lakes, rivers, or oceans. This is not only an unsanitary and smelly situation but depending on the amount of FOG and time it has been collecting, there may be millions of gallons of FOG to clean up. The frequency of these overspills can cost a city millions of dollars in maintenance, health and environmental fines.

As a consequence, municipalities spend lots of money cleaning sewer pipes as prevention measures to keep sewage pipes operational and functional. Operators involved in waste water treatment also want to ensure that the water treatment process is not severely slowed down due to the challenge. Although grease traps are in place in businesses where FOG generates, plenty of FOG makes it across the network of wet wells in most cities. Since pumps and generators are not designed to handle the extra scum, the end result is a slowdown of the treatment process and an increase in maintenance cost. In an ideal world, all of us would make sure that debris or greasy matter does not go in to the sewer system by disposing of it in other ways, rather than down the drain. An ounce of prevention could save us all lots of money because at the end, we all pay one way or another.

Back to reality

The fact remains that FOG is an ever increasing problem. All you have to do is search for images of wet wells with FOG and you will see that in some cases the amount of fat in a wet well is astonishing. I have seen surfaces with so much of this stuff on it that not even a concrete masonry block can break through it (an extreme case). Waste water treatment operators use substances and mechanisms that aid in its reduction, but it seems that dealing with FOG is a reality that is here to stay.

So what else can be done to reduce some of the maintenance costs associated with this fatty issue?

Is there room to save time and money when dealing with FOG? The answer is yes by utilizing the wall cling reduction function found in ultrasonic level controllers. Any time there is an opportunity to reduce maintenance, this equates to saving time and money. For example, the issue with FOG is not only with the sewage pipes but its effect manifests across the wet well network and they too need to be maintained to prevent equipment malfunctioning and avoid or reduce overspills. One of the big issues that you want to avoid is false level readings from level devices (in case of the level sensor is mounted too close to the wet wall.) Granted, not all geographical regions create FOG equally. The fat ring builds up in some wet wells can be light to severe depending on the industries and population make-up in the area. If you could reduce the frequency of trips to offending areas by 20% or even just 10%, this means that you will be using less manual labor with not as many degreasing agents and you would reduce your distance to and from sites for maintenance. Depending on the size of your operation, the savings can translate to thousands of dollars year-after-year.

How do you implement wall cling reduction?

If you’re using an ultrasonic level controller, like a SITRANS LUT400 or a HydroRanger 200 HMI, use the “Wall Cling Reduction” function to randomly alter the “ON” and “OFF” set-points over range. This eliminates the ridge of material that builds up at the set-point, thereby increasing the number of days between trips to clean the wet well.

On the SITRANS LUT400 or HydroRanger 200 HMI, you want to:
Enable the “Wall Cling Reduction” function.
Set the range in “Level Set-point Variation.”

The result: the pump “ON” and “OFF” set-points are randomly varied. Inside the pre-defined range, the material level does not stop at the same point each time.

For example: A range of 2 feet is used to vary the set-point. The randomly selected set-points are always inside the “ON” and “OFF” set-points. See figure below.

Eliminating FOG from entering the sewage system will be the ideal scenario. The reality is that it would take a lot of education and commitment by all industries and the public to see the negative effects this causes to the environment and to the water treatment process. Implementing something as simple as Wall Cling Reduction does not eliminate the issue, but it can help mitigate some of the maintenance costs associated with it.

Please join us at the 2017 WEFTEC Expo (booth #1617, South Hall) to discuss these solutions in further depth. We would be happy to answer any questions you have regarding your process and how you can relieve some of the FOG issues that you may be experiencing.

How are you addressing external influences that interfere with your level measurement devices?

Source: https://blogs.siemens.com/en/measuring-success.entry.html/2017/09/29/40645-how-to-deal-with-too-much-fat-oil-and-grease-in-your-wet-wells.html



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