Nitrification and low temperature in a raw water reservoir and rapid sand filters

Ammonium removal occurs in both the surface water reservoir and rapid sand filters of Amsterdam Water Supply. Nitrification in the reservoir is best modelled as a first order reaction with a temperature dependent breakdown coefficient. In moderate winters, the increase of ammonium concentration in the filter influent is compensated but stagnation of nitrification in the Winter of '95–'96 led to a two and half month excess of the ammonium maximum admissible concentration. Only after the start of phosphate dosing, full restoration of nitrification was achieved. A model to alert for ammonium breakthrough was developed based on growth characteristics of Nitrosomonas .