Impact of temperature on nitrification in biological activated carbon (BAC) filters used for drinking water treatment

The impact of temperature on nitrification in biological granular activated carbon (GAC) filters was evaluated in order to improve the understanding o f the nitrification process in drinking water treatment. The study was cond ucted in a northern climate where very cold water temperatures (below 2 deg reesC) prevail for extended periods and rapid shifts of temperature are fre quent in the spring and fall. Ammonia removals were monitored and the fixed nitrifying biomass was measured using a method of potential nitrifying act ivity. The impact of temperature was evaluated on two different filter medi a: an opened superstructure wood-based activated carbon and a closed supers tructure activated carbon-based on bituminous coal. The study was conducted at two levels: pilot scale (first stage filters) and full-scale (second-st age filters) and the results indicate a strong temperature impact on nitrif ication activity. Ammonia removal capacities ranged from 40 to 90% in pilot filters, at temperatures above 10 degreesC, while more than 90% ammonia wa s removed in the full-scale filters for the same temperature range. At mode rate temperatures (4-10 degreesC), the first stage pilot filters removed 10 -40% of incoming ammonia for both media (opened and closed superstructure). In the full-scale filters. a difference between the two media in nitrifica tion performances was observed at moderate temperatures: the ammonia remova l rate in the opened superstructure support (more than 90%) was higher than in the closed superstructure support (45%). At low temperatures (below 4 d egreesC) both media performed poorly. Ammonia removal capacities were below 30% in both pilot- and full-scale filters. (C) 2001 Elsevier Science Ltd. All rights reserved.