We experience problems with ...
Published by Waymon Hofheins
We experience problems with deposits of elementary sulfur in our waste water treatment.
Elementary sulfur deposits is strange. Are you sure you are not getting a sulfur salt, not elementary sulfur. Sulfate deposits used to be quite common in the 40s and 50s when sulfuric acid was used to lower the pH in cooling towers - that was before the use of some materials that allowed the cooling towers to operate at a higher pH. Taking the pH down with the use of chromate and zinc allowed for good corrosion protection at a low pH. It kinda sounds like you are taking the pH down to this extremely low level to control some other deposits (look at the Langelier index, and others). The bacteria will function better if it is operating at a higher pH, up to 7.5 or even 8.2. So, why are you at 6.91 pH? Can it be raised? "This is to the point where metal parts are corroded away, although our pH measurement is still relatively neutral (average 6.91 with standard deviation 0.27)."
A 6.91 pH can be very corrosive. This could be a problem. Look at Langelier and others.