Union Rome is a 2.2 MGD Membrane Biofilter(MBR) plant. We have been battling this problem for a while now. We have tried feeding a baking soda solution but still would have great effluent pH's for weeks and then all of a sudden it would drop to 6.3 or 6.4. Then we received information that a soda ash solution gave a more stable reading so we changed to that. Same scenario - great for a while, then drop below our lower limit. We've increased detention time the soda ash comes into contact with our effluent - same scenario. We've moved our solution feeds around to different areas of the plant, also changed the strength of the solution as well as the pace it's fed. It hasn't really helped.
We've considered that we are being dumped on but it's so random and by the time we get the low pH, it's taken 24 hours to go through our plant so there's no way to track it back. We've also tried to tie it to some kind of event in our plant - like an equipment failure, or blowers kicking out, or some occasional operational changes. No luck finding a link.
If anyone has experienced this or has any ideas we haven't thought of, your advice would be greatly appreciated.