Thursday, June 4, 2009

Battle Of pH

Author: Hong Ting (Sam) Chiu

The plan of the day was to start the batch experiment. However, it didn't happen as we anticipated. It was because we are in the "Battle of pH." Our experiment requires 24 bottles to be run at pH 6, 7, and 8. However, based on the trials ran yesterday, we are having difficulty to maintain the pH at the intended value (within ±0.1) over time. Therefore, we decided not to start the batch experiment; instead, we look further into ways to fix the pH and keep trying.


The 24 bottles are ready to go; but pH isn't.


The two trials from yesterday :(


Chemicals and equipments are also ready.

Due to the large variation, we discarded the trials from yesterday and started another two with a more systematic plan of attack. The first one, we decided to take a baby step: mix the calcium chloride, the sodium bicarbonate, the arsenite, and the granular ferric hydroxide (GFH); let it mix for one and a half hour at 100 rpm without any disturbance; record and observe how to pH varies with time. It seems that the pH converges in about 15 minutes and has minimize changes after on. We then decided to make the second one (with the same content), but adjust the pH with sodium hydroxide. The pH doesn't stay stable over time. We have to intervene: spike the pH up with sodium hydroxide from time to time so that it maintains the pH within ±0.1 of the intended value.


The bottles on a shaker with a pH probe for monitoring.


pH at 7.54 - because we just spiked it up.


The result of the first bottle.


The result of the second bottle.

Now, we are off at the dorm. However, the shaker and the pH meter are still running at UNESCO-IHE (Do we still count as "working," since the shaker, the pH meter, and our brains are still working?? Haha); we will see what the overnight results will look like tomorrow. If the pH doesn't drop too much and we can start the actual batch experiment really soon.

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