Vincenzo Scarlata, Proprietario, Bioflot: Can be interesting to know your final effluent quality, the volatile fraction of your sludge and the characteristic of your settling basin.
Having SVI 150, it is difficult to correlate sludge quality with high TSS in the effluent. Your F:M based on the data you wrote is low. If your effluent is acceptable for COD, BOD and nitrogen, you can try to decrease MLSS concentration to decrease the solid loading on your settling basin.
The effect of SRT modification requires some days to be appreciate. Working with a pilot plant, the rule is to wait three times the SRT before, to start the analysis. Your D.O. is very high but I don’t think that can create problem in settling basin, you are only consuming energy without necessity. I don’t know your aeration system but you can study to apply inverter or timer. If your D.O. in the night increase from 4 to 6mg/l or you have less inlet load or you might have a transient toxic.
I agree with Fuller if you have high TSS in the effluent the first action is to try to save the situation with a polymer that can give you result in few hours. In any case, I know of an industrial plant where the use of polymer is practically constant. Other important point is to check and if necessary to add phosphorus.
Hector Fernandez, GM-HI Group, LLC: Polymer is like an aspirin to the flu, it helps but it is not the solution.
Ryan Hennessy, Lead Operator/ In house microscopy-Woodard & Curran: I’ve seen some plants that have the ability to adjust the amount of RAS that goes to the selector further along in the aeration basin. In these configurations it is possible to send less RAS to the selector to bring the F:M ratio in the selector up (drive the ORP down for denitrification).
Polymers in some situations can be a necessary evil. Polymer to the clarifier in large wastewater treatment plants with high flow should be avoided (very expensive!) In indu
strial plants that run >100% design hydraulic capacity sometimes they live with this cost (cheaper to sustain this than to build a new clarifier or add a DAF on the back end- no capitol money available). In smaller plants that have I and I issues having polymer available for higher flows is sometimes very useful.
Amit Christian, Country Representative-Levapor Biofilm Technologies & Bio Consulting, GmbH: To the original question, I think the problem is quite complex than one thinks. As it is mentioned that the DO level falls during certain times and gains again after a while. This could be due to shock loading of the toxic pollutants.
Another possibility is denitrification which is not functioning and thus the regaining of alkalinity which was assumed during design phase is not occurring and dropping the pH of the effluent and at the same time disturbing biological activity and thus settling properties of the sludge. Under low BOD conditions, if not enough rbCOD is present then the nitrate recycled would not be denitrified and thus, there would not be any gain of alkalinity. The higher concentration of TKN in the inlet would consume more alkalinity due to favourable conditions for nitrification (low BOD, F:M ratio) and at the worst case scenario if the alkalinity input is not suffice during the high TKN events, you loss optimum pH range in the reactor, losing biological activity.
