Quantitative control of biochemical pH
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For water treatment, is it better to use light or heavy sodium carbonate? Also, are there any ways to distinguish between the two? Soda ash is added on-site to control the pH, but it’s difficult to determine the exact amount to use. Is there any good way to calculate it, or does one have to rely solely on the changes in pH after addition?
It is more accurate to conduct experiments in the laboratory, as certain substances present in wastewater, such as phosphoric acid, have a buffering effect on pH, which means that the calculated values may not be precise.
We add acid and alkali chemicals to the reaction tank and stir them; there are connected tanks following that, where stirring and online monitoring take place
Light soda ash was added to the anaerobic-aerobic tank on site, with almost no change in pH, indicating an exceptionally good buffering effect
However, this may also be related to the operating conditions of the on-site biochemical equipment; the laboratory cannot replicate them completely
It is best to adjust the pH value before entering the aerobic tank, with it generally being kept between 6.5 and 7.5； If denitrification is also required, alkali must be added at the inlet and in the middle of the aerobic tank to adjust the pH.
The concentration of the added alkali should not be too high, otherwise mixing will be uneven and it can easily lead to a deterioration of the local environment, which is detrimental to the activated sludge.
The specific situation is that the pH of the raw water is around 8.0. Pretreatment denitrification is carried out on-site, and the equipment has been in operation for nearly 3 months. In the anoxic tank, the pH has remained around 6.8 over the past one and a half months (while it is 7.1 in the aerobic zone). Attempts have been made to add soda ash to the anoxic tank, but with little effect
Alkali is added to the aerobic tank to adjust the pH value in order to ensure an efficient nitration reaction. With an aerobic pH of 7.1, it can be seen that the nitration reaction is not inhibited; if a low pH at the aerobic outlet is caused by the nitration reaction, it can generally drop as low as pH 6.5.
Can’t you measure a few more points?