Dissolved Air Reactors
A second activated sludge process utilizes diffused air for nitrification,which is the conversion of ammonia (NH4-) to nitrate (NO3-) is provided in open reactors in combination with the final sedimentation tanks. Carbonaceous stage effluent enters the reactors in a plug flow pattern and is combined with the return sludge to form mixed liquor. Because of the high BOD5 and suspended solids removal efficiency of the carbonaceous stage, a regulated stream of primary treatment effluentcan bypass the carbonaceous stage and be fed directly to the nitrification stage to supplement the food supply required by the nitrifying bacteria. Air for the system is provided by centrifugal compressors and a membrane diffuser system.
In the final sedimentation tanks, the solids (activated sludge) are removed from the mixed liquor by gravity settling. The solids may then be returned to the reactors or wasted from the process, as required.
At this point in the process, the removal of carbonaceous BOD5 and suspended solids is expected to be approximately 95 percent. More than 95 percent of the ammonia nitrogen in the influent to this activated sludge system will have been converted into nitrate-nitrogen as well.