A Field Comparison of Methods for Estimating Nitrifier Maximum Specific Growth Rate in Treatment Plant Design – The Case Against WERF's High F/M Method

The nitrifier maximum specific growth rate (mmax) is arguably the most important parameter for estimating reactor size in a biological nutrient removal (BNR) system. The authors used three methods to establish the design mmax value for the enhanced nutrient removal (ENR) upgrade at the Little Patuxent Water Reclamation Plant (LPWRP) in Howard County, Maryland. Statistical analysis of the high F/M data set indicated a high degree of correlation between seed size and the nitrifier maximum specific growth rate estimate. This is contrary to the premise under which the test was developed but is consistent with the author's observations for other studies conducted by several reputable laboratories on similar projects. This study concluded the low F/M method is superior to the high F/M test for the reasons cited.