Sludge Removal


Thanks to Luis Margheritis for today’s photo, which is of a newly revised sludge removal process. It seemed to be better than a picture of actual sludge for today’s topic.
I have been fortunate to work with over 60 different water and wastewater treatment plants around the country, and in the process encounter well over 1000 Operators. I feel as though I have learned something from each of you, even though you thought you were supposed to be learning something from me.
As you might expect, I have encountered some outstanding Operators. And I have encountered some poor ones, too. One of my worst experiences came about 25 years ago at a wastewater plant in Louisiana. But I did learn something from that crew, and I hope you do as well, through today’s blog.
My initial role at this plant was to assist the crew in starting up a new plant, which was built adjacent to an existing plant. So the crew should have been quite experienced. I guessed at the initial control settings for the pumps that removed sludge from the primary clarifiers. The settings were pretty typical for a plant of this type and size, with pumps set to run for 5 minutes, and then idle for 10 minutes, or something close to that. The crew was supposed to do what any responsible crew would do: adjust these timers up or down, in response to actual plant operating conditions.
About a year later, I was summoned back to the same plant, because it was having difficulties meeting its quality targets. The crew reported that they had experienced problems with the primary sludge pumps, and so they replaced them! I was stunned that these units had lasted less than a year — with proper O&M, they should have provided a couple decades of satisfactory operation.
While they replaced the pumps, they kept all the original pump controls, including the timers. Despite the installation of the new pumps, the timers were set exactly as I had set them! These guys didn’t have a clue as to the most basic operation in a wastewater plant!
This led me to an adage I’ve developed over the years: A good Operator can make any plant work; a bad Operator can’t make any plant work!
Proper sludge removal has three key objectives:
First, sludge in must equal sludge out.
Second, sludge is mostly water, and leaving sludge in the clarifier longer allows the sludge to thicken, and squeeze out some of the water. This is good, because it means less pumping cost, and it can significantly improve sludge processing operations.
Third, you can have too much of a good thing, in terms of leaving the sludge in the clarifier. Sludge that is too thick to pump is of no use. And leaving sludge too long in the clarifier can allow it to go septic, with off-gases actually causing some of the settled sludge to float away — exactly the opposite of what we are trying to achieve.
The way to reach these three objectives is by adjusting the pump timers. And this can only be done in response to actual operating conditions. Only an Operator can do this. And only a good Operator can do it well!

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