Chalk as the carrier for nitrifying biofilm in a fluidized bed reactor

A fluidized bed reactor for nitrification with chalk as the biomass carrier and the sole buffer agent was studied. Chalk dissolution in the reactor wa s found to follow the stoichiometric ratio of 1 mole of CaCO3 dissolved for each mole of Nh(4)(+) oxidized. Three batches of chalk, each one having a different dissolution rate, were used to replace the dissolved chalk. The t hree dissolution rates resulted in three different steady state pH levels i n the reactor (4.7-6.6) and nitrification rates. Nitrification was found to be limited by either the chalk dissolution rate or dissolved oxygen concen tration depending on the type of chalk used. A maximal nitrification rate o f 1.44 g NH4+-N/l reactor . d was observed. The average cell yield was 0.1 g cells/g N oxidized, similar to the cell yield during reactor start-up whe n the pH was 7. The specific ammonium oxidation rates varied between 0.08 a nd 0,15 mg NH4+-N oxidized/mg protein . h. values which are in the reported range For nitrification at pH 7 to 8. Oxygen update rate (OUR) results ind icated that the major mechanism responsible for the high nitrification rate observed in the reactor operating at low pH seems to be the favorable micr oenvironment provided by the chalk. (C) 2000 Elsevier Science Ltd. All righ ts reserved.