The presence of ammonia during drinking water production can be the source of several water quality problems during distribution and during disinfection when chlorine is used. It is therefore important to optimize the ammonia removal before disinfection. The purpose of this work was to compare nitrification on an opened superstructure (Picabiol) and two closed superstructure (Picacarb and Calgon F400) granular activated carbon (GAC) during colonization of new filters and after longer operating times in pilot and full-scale filters. Fixed nitrifying biomass levels, ammonia removal and oxygen consumption were monitored at high and low temperatures and at two different ammonia loadings. In first stage pilot filters supplied by an ammonia concentration higher than 0.4 mg l−1 N-NH4 and at temperatures higher than 20°C, nitrification capacity was higher on Picabiol than on Picacarb. At low temperature, no ammonia removal occurred on both materials. Calgon and Picabiol provided equal nitrification performances. In full-scale second stage filters fed with ammonia concentrations ranging from 0.02 to 0.16 mg l−1 N-NH4, nitrification performances were similar on Picabiol and on Calgon. In cold water, none of these filtration materials provided a proper nitrification; nitrifying biomass, however, did not disappear on the GAC filters during winter.

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