[marsh]

Randy,

I agree the to regulate Ca reactor variables so as to match system alkalinity consumption with Ca reactor alkalinity output given calcium levels do not rise. My arguement has to do with simplifying Ca reactor setup.

The way I handle alkalinity is to measure the alkalinity of the final effluent and adjust the drip rate of the effluent to match tank consumption. I keep my pH in the reactor chamber near a set point to dissolve media but not disintegrate it and thus maintaining a constant effluent alkalinity. In this way only one variable is changed, effluent drip rate, to match alkalinity consumption. My assumption is that with a pH contoller, with the probe in the reaction chamber, the alkalinity of the effluent will be constant over a wide range of drip rates. This gives a relatively wide dyanamic range in which to match alkalinity consumption with reactor alkalinity consumption by changing one variable, effluent drip rate. It also considerable simplifies reactor "tuning".

Your method, I assume, alters the CO2 bubble rate so as to dissolve media and not disintegrate it but keeps the drip rate constant. Altering the chamber pH by adjusting the CO2 bubble rate alters the effluent alkalinity which with a constant drip rate matches tank alkalinity consumption. Again changing one variable, CO2 bubble rate? Or do you also change the effluent drip rate? If only the CO2 bubble rate is altered to match alkalinity output with consumption, I believe, you are limited by the accuracy of bubble counting, bubble rate incremental change, effluent pH measurement and perhaps by dynamic range of your alkalinity adjustment. The dyanamic range of alkalinity output at a constant drip rate is limited by a pH range of 6.5 to ?7.6. Is this a real issue? Also is the change in alkalinity linear with reactor pH change? If you also alter drip rate I presume you will also alter the effluent alkalinity at a set bubble rate as the dwell time changes. Is this actually an issue with reasonable incremental changes in drip rate? Anyway, once set with alk output equal to consumption, everything is copacetic. However, the matching process takes a good while just changing one variable.

I do not have a dual chambered reactor, but the intial question had to do with lowering the final effluent pH of a dual chambered reactor. The final effluent pH is ~7.0 making the 1st chamber ~6.5-6.7. Increasing his CO2 bubble rate to increase effluent alkalinity to match tank consumption would put the media in the first chamber at risk. For example, an effluent pH of 6.5 would mean the 1st chamber pH is 6.0- 6.2 or so putting the media at risk. Decreasing the CO2 bubble rate and thereby increasing the 1st chamber pH/decreasing effluent alkalinity may also place the pH in chamber too high for the 2nd chamber media to be of use in terms of alkalinity contribution. I always thought the 2nd chamber was mainly to increase effluent pH and not alkalinity anyway.

IMHO a ph controller with the probe in the first reactor chamber will simplfy setup and will put his 1st chamber media at less risk. In another thread his effluent pH was 6.5.