Hello everyone


I work at a Modified Ludzack-Ettinger WWTP here in Florida and we are permitted for annual average daily flow of 7.5 MGD.  Currently the plant treats wastewater at AADF of ~5 MGD.  Our influent BOD strength remains relatively constant ~ 250 mg/l ± 50 year round and we run the plant with the aeration MLSS 2800 – 3500.

Everything seems backwards from what the books say about the settleometer and wasting (we waste more in the winter less in the summer).  More MLSS is needed treat same amount of BOD due to temperature change.  I asked the older operators about this and they tell me it’s due to the plant being below capacity.

My question is what aspect of being below capacity would cause the plant to behave as it does?

By the way we have been through hurricanes to very dry weather and nothing seems to affect the plant.                        

                                                                                              Thanks

sludge yield is actually higher as the temperature decreases. This is because the metabolism of the bacteria is slower and there's less endogenous activity. (which is basically the bugs eating themselves). This is normal, especially in a longer sludge age BNR plant like yours.

I've found at a few plants that I can run a lower sludge age in the summer due to this where I need to wase a little more in the winter. The MLSS (and the F/M stays the same even with the lower wasting rate).


Also don't waste based on the settleometer. This gets a lot of people in trouble. Certain things will give you a higher SVI and need to be identified microscopically if you see the SVI increasing.

best regards,

Ryan