Sean Scuras is Garver’s National Practice Leader for Wastewater Treatment and an Adjunct Assistant Professor at Clemson University. A former WWTP operator, Dr. Scuras has over 40 years of experience in the wastewater field. He has a BS in Engineering from Southern Illinois University, an MS in Civil Engineering from the University of Colorado at Denver, and a PhD in Environmental Engineering from Clemson University. His specialties include nutrient removal process design, optimization, troubleshooting, and operator training.

To reach very low effluent nitrogen levels requires attention to all nitrogen species:  ammonium (NH4-N), nitrate (NO3-N), nitrite (NO2-N), particulate organic N (PON), and dissolved organic N (DON).  Together these are known as total nitrogen (TN).  NH4, PON, and DON are TKN.  NOx is NO2 + NO3. Some DON is recalcitrant and remains in the effluent as rDON.  Some PON may be removed in primary clarifiers.  In the bioreactor, much of the PON and DON will be converted to ammonium.  Some of the ammonium is removed by assimilation into biomass as growth occurs in the bioreactor.  The higher the BOD into the bioreactor and the shorter the SRT, the more nitrogen is removed by assimilation.  The non-assimilated non-recalcitrant nitrogen is available for nitrification and denitrification processes.  Although nitrification to convert ammonium to NOx is straightforward, adequate safety factor over the minimum aerobic SRT is needed to provide the consistent and complete nitrification that is essential to meet very low nitrogen limits.  Many processes recycle the nitrified flow to an upstream anoxic zone for denitrification of NOx to N2.   Even with an adequately sized anoxic zone and sufficient carbon, there is a practical limit to the fraction of the wastewater that can be recycled for denitrification so that most processes are capable of no more than 80% denitrification using this approach thereby leaving 20% of the NOx, the rDON, a bit of PON associated with the ETSS, and a bit of NH4-N.  When these are > TN limit, a second denitrification stage is required.  This talk will use examples to explain these relationships so that operators and managers can be prepared for upcoming discussions of process capabilities, TN limits, and process modifications to maintain compliance.  One of the example processes is achieving TN < 2 mg/L and TIN < 0.5 mg/L.