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RE: pH problem

david jenkins — Wed, 14 Mar 2007 11:42:59 GMT

I just reread your post and noticed that you stated that, in summer when the pH gets to 10 or so, you can see the bottom of the pond. This observation also fits with what I posted last evening. When the pH gets that high you can precipitate calcium carbonate. This precipitate flocculates/weights down the alge and the aggregate of CaCO3 and algae then sinks to the bottom of the pond.

RE: pH problem

david jenkins — Tue, 13 Mar 2007 20:41:46 GMT

Here is a highly simplified picture of what is happening:

1. The pH of natural waters, including wastewaters is controlled by the concentrations of alkalinity and dissolved carbon dioxide in the liquid.

2. The higher the alkalinity the higher the pH and the higher the dissolved CO2 content, the lower the pH.

3. When algae photosynthesize they consume CO2 from the liquid.

4. If the consumption rate of CO2 by the algae exceeds the supply rate of CO2 to the liquid then the CO2 concentration in the liquid will go down and the pH will go up.

5. CO2 is supplied to the liquid from two sources:

(i) the respiration of the algae and bacteria in the liquid

(ii) by transfer from the air across the water surface into the pond liquid.

These combined sources of CO2 to the liquid can be easily exceeded by the CO2 uptake of an actively photosynthesizing algae pond.

6. Your observations are completely consistent with this picture since:

(i) the pH goes up during the day when photosysnthesis is active

(ii) the pH goes down at night when photosynthesis stops but respiration continues.

Knowing that this is a problem with not being able to supply CO2 fast enough to keep up with the demand of CO2 from photosynthesis leads to a possible solution: If you were to install a surface mixer in the pond then you could increase the CO2 input from the respiring bacteria at the bottom of the pond and increase the CO2 transfer into the pond from the air. Also, you could take advantage of the drop in pH and night by only discharging from the pond at night. Another way to do this is to bubble air into the depth of the pond to encourage mixing and turnover.

RE: pH problem

GaryS — Tue, 13 Mar 2007 13:31:47 GMT

chance (4/26/2006)

The pH is running at 9.7, even during the evening hours. By mid to late summer, you can see the bottom of the cell and the pH runs at 10.0.

...

How late in the evening? We had a strip chart recorder on one pond where you could observe the trend. The pH would start going up in late morning, and would stay elevated until well after midnight before it would trend back down. What you're describing fits what I've observed with pond pH swings due to algae. Our ponds can run fairly clear, certainly not green and still have pH's as high as 10.

RE: pH problem

Al Temple — Mon, 08 May 2006 09:39:33 GMT

I may be able to help you as we have completed many WWTP in North Dakota. If you are interested please call me LAS International. Al Temple 701-222-8331.

RE: pH problem

John Sansalone — Wed, 26 Apr 2006 17:33:04 GMT

In natural water systems (ponds, lakes, etc.), algae can cause big swings in pH - pumping up the alkalinity and D.O. during the day, respiring (and causing a drop in D.O. / pH ) at night. This can be the case even when the algae is not so obvious, because of growth on the bottom. You might want to check those parameters several times over the course of the day, and see if it fits this pattern. If so, might want to think about things like grass carp, to keep it in check.

pH problem

chance — Wed, 26 Apr 2006 16:36:36 GMT

I was wondering if I could get some assistance with a two cell lagoon system. The system does not have any problems meeting effluent limits, except for pH.

I live in South Dakota so the lagoons are froze over during the winter months. The pH within the secondary cell was around 7.2 to 7.5 all winter and when the ice came off, it jumped up to around 8.7.

There was some algae that started to grow on top of the cell for about three weeks and the amount of algae became less and less. Right now, you can see three to four feet into the water. The pH is running at 9.7, even during the evening hours. By mid to late summer, you can see the bottom of the cell and the pH runs at 10.0.

The alkalinity of the water is 264, so it isn't an alkalinity problem. BOD and TSS are single digits and ammonia is less than 1.0.

Is this caused somehow due to no nutrients in the water?? Does anyone have any ideas. Thanks...