the liquid in the time allowed for the decant cycle because the decanter lip or inlet is always below the liquid level in the tank it is not affected by freezing or any ice build up at the surface of the tank if operated in very cold climates it also prevents floating scum from being discharged with the effluent and affecting its quality tests have shown that any mlss settled in the space between the trough and the deflection baffle will be resuspended when the next aeration cycle is started due to the air that is allowed to collect under the trough and be expelled through numerous air relief holes located in the space between the trough and deflector of the inventive device dye tests and specially treated sawdust used to simulate activated sludge have been used to verify that even with the sludge blanket just at the bottom of the decanter the low inlet velocity and the deflectors do not allow the sludge blanket to be disturbed it is often desirable to use an sbr for nitrate reduction prior to discharging nitrate reducing bacteria thrive in an anoxic atmosphere such as is present after decanting and before aeration this.