I am trying to find a long-term solution to stabalizing a settling pond that sometimes receives a high loading of sugar that decreases the pH to around 4-5.  The retention time of the settling pond is 1 day, from which is moves to our Aeration Pond and then to be discharged to the river.  Our discharge permit is pH 6-9, and it's a constant battle of adding caustic/soda ash to the settling pond every day.  I am curious if somehow I can add a lime slurry to the settling pond in which the lime mixture will settle and leach out its alkalinity and thus stabalize the pond to a high enough pH that when high loading of sugar is introduced to the pond, it will dilute it enough to proceed safely to our aeration pond.  Does this sound scientifically/chemically possible, or will the lime even settle to the bottom and mostly remain there as I hope?  Thanks and any advice is appreciated.  I have researched lime and I haven't come upon a problem or a solution as the one I present.  'thanks again.

I'm by no means an expert in ponds, but I'd expect the setting pond to be after the aeration pond. It sounds like due to the lack of oxygen and the high amount of readily available "food" -the sugar you're producing volatile acids under anaerobic conditions which is lowering the pH. Does the pH fluctuate during the day due to high amounts of algae? If pH the only parameter that is tough to meet?

kristoph:

It sounds like you are producing organic acids from sugar fermentation in the settling pond. Probably best to aerate this to slow this down. Lime does "time release" if overdosed, however, if too much is added, the pH can go to 11 or above and affect the subsequent biological treatment. Best to add magnesium hydroxide, which has limited solubility (pH 9.5 at the highest) and it slowly does "time release" to keep the pH up.

Hope that this helps.