P Removal: A Better Way

Share Your Idea Tips and Tricks is an occasional feature of TPO in which wastewater operators tell how they took innovative measures to solve problems.
P Removal: A Better Way

We have an oxidation ditch system. Since the plant was started up in 1987, we have been feeding alum for phosphorus removal at the head of the plant. We have four channels: The two outer ones are used to treat the waste, and the two inner channels are used as digesters. Normally, we use the outermost channel (Number 1) for treatment and Number 2 for heavy flows and backup. We decided to drain and clean the Number 1 channel and switched to Number 2 for treatment.

When we drained the Number 1 channel, we found a large amount of solids that had settled below our aeration disks right where the alum was feeding to the plant. I asked Donna Lawson, wastewater technician II with the Virginia Rural Water Association, to stop by, look at the situation, and give us feedback and suggestions. She immediately questioned why we were feeding alum at the head of the plant right where our raw wastewater came in. The only reply I could give was, “It has been done that way for 20-plus years.”

We agreed that alum should be fed at the splitter box just before the clarifiers. The piping was already in place, and turning two valves was all it took to make the change.

Our permit limit on phosphorus is 2.0 mg/l monthly average. When feeding alum at the head of the plant, our phosphorus tests were averaging 1.0 to 1.3 mg/l, well below our limit. We were feeding about 190 to 200 gallons per week.

After switching to the splitter box feed, we cut our alum usage in half to 95 gallons per week, and our phosphorus is running 0.3 to 0.4 mg/l per test. This is saving us about $1,800 every eight months.

As operators we do some things because, “That’s the way it has always been done.” I know we have to be careful and always keep our permit limits in mind, but we can take calculated small steps that can improve our plant operations.


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