Comparison of Methods to Evaluate Nitrification Kinetics: WERF “High F/M” and “Low F/M” Protocols

Water Environment Research Foundation (WERF) presented three methods targeted to improve the accuracy of nitrifier maximum specific growth rate (μ_max) measurements: High Food to Micro-organism (F/M), Low F/M, and the Washout methods (2003). By reducing the time and effort required, these methods encourage direct measurement of μ_max for each wastewater treatment facility, instead of relying on textbook values with added safety factors. Reducing the design μ_max has a significant impact on cost of nitrification, in that a small percent increase in μ_max can result in a significant decrease in required aeration volume, and thus a significant cost savings.

The High F/M, Low F/M, and Washout Methods utilize different experimental protocols, and each presents different advantages. This work focused on comparing results from the High and Low F/M methods at two different wastewater temperatures. In addition to steady-state comparisons, temperature shock tests were performed to investigate each Method's effectiveness at estimating μ_max during temperature change, to determine whether such shock tests can be used as surrogates for the time-consuming process of developing temperature-acclimated biomass. New biomass is produced during the High F/M method, but not (theoretically) during the Low F/M assay, suggesting that the two methods respond very differently to temperature shock testing. The performance of either method under laboratory conditions during temperature shock testing has yet to be demonstrated definitively.