The effect of CO2 concentration on a nitrifying chalk reactor

The effect of CO2 concentration on nitrification rate was studied in a fluidized bed reactor using chalk (solid calcium carbonate) as the biomass carrier and buffering agent. Using one chalk type and uniform particle size, carbon dioxide was found to limit the nitrification rate in the reactor at concentrations up to 0.3 mmol l−1. At this concentration the nitrification rate was about 2.5–2.7 g NH4+–N l reactor−1 d−1. The pH established in the reactor varied between 4.5 and 5.5, remarkably with lower pH obtained remarked at higher nitrification rates. Kinetic parameters for nitrification rate with CO2 as the rate limiting substrate were determined: a Michaelis–Menten constant, Km, of 0.013 mmol l−1 CO2 and a maximum ammonium oxidation rate of 2.33 g NH4+–N l reactor−1 d−1.