MYTHS OF NITRIFICATION TALES OFTEN TOLD THAT ARE NOT TRUE

The design, construction and/or adaptation of wastewater treatment plants for nitrification have been occurring for approximately thirty years. Over this time the basic principles of nitrification have either been ignored, elaborated upon, modified and, in some cases had falsehood presented as truth. These myths about nitrification includeThe required solids retention time (SRT)The required hydraulic retention time (HRT)That the BOD must fall to 20 mg/L before nitrification occursThe need for two-stage treatmentThe settling properties of nitrifying sludgeThe allowable surface overflow rateThe mixed liquor dissolved oxygen (DO) requiredThe return activated sludge (RAS) flow requiredThese myths are examined and shown to be untrue, or at least not true in many instances, and restrict the operators' ability to produce good effluent under a variety of conditions. The paper shows a rational basis for design and a performance envelope for nitrification.