Alum addition for P removal 2

[DrLewinstein]

We are working on a 1 mgd activated sludge plant that has a 6 month rolling average pound limit for phosphorus. No concentration limit. The plant presently meets this limit without P removal, but could in the future have to remove some P to meet compliance if flow increase. We plan to add alum into the pipe between the aeration basin and the clarifier. M&E says this is acceptable practice. The operator says we should actually have a mixing tank prior to the clarifier. He also says we should add caustic also to maintain pH. I could understand adding caustic if we were adding lots of alum but this seems excessive just take out some pounds but not have a concentration limit. Any thoughts?

Thanks

 

[bimr]

One of the reasons that alum is used is because it effective in the pH range of activated sludge systems.

Increasing the pH of the system with caustic will be extremely expensive. Suggest you ask the fellow where has he does this before.

If you can get approximately 4 changes in direction, the alum will be mixed in adequately. You can also increase the flow of the carrier fluid.

 

[QualityTime]

Wastewater normally has a lot of alkalinity and is therefore resistant to pH change. The addition of alum will not decrease the pH very much. Every 1 mg/l of alum uses up 0.45 mg/L of alkalinity (as CaCO3. Do jar tests to determine what the resultant pH and what the resultant alkalinity is