Determination of Nitrifier Growth Rates in NYC Water Pollution Control Plants

New York City DEP in collaboration with the City College of New York has developed a step-feed BNR process that has demonstrated significant nitrogen removal. The process is being considered for implementation at several water pollution control plants. Several bench scale and pilot studies have been initiated to develop design criteria for step-feed BNR. In this paper the methods used to measure maximum specific nitrifier growth rate, μA and nitrifier decay rate, bA are presented. Sequencing batch reactors, SBRs, operating on primary settling tank effluent have been selected to measure μA. The SBRs are operated for a minimum of three SRTs to allow for acclimation of the nitrifiers and achieve pseudo steady-state conditions. Subsequently, nitrification rates are measured and using the BioWin model to simulate SBR operation, μA is calculated. Biomass from the SBRs is also subjected to starvation operating conditions in order to measure bA. Data from one of the studies is used to illustrate the method and also underline the importance of measuring both μA and bA for a given wastewater.