A pilot study of biological GAC filtration in drinking-water treatment

The impact of empty-bed contact time and temperature on the efficiency of biological GAC filtration has been studied on pilot filters at the Neuilly-sur-Marne treatment plant. Fixed bacterial biomass was investigated using a method of potential respiration of labelled glucose and the filtration efficiency was characterized by the removal of biodegradable dissolved organic carbon (BDOC). With a fixed bacterial carbon biomass of c. 2 mg/l, pilots with empty-bed contact times of 10 min removed around 60% of BDOC. The net exportation of bacterial biomass was very low when compared to the removal of BDOC achieved by the filtration. BDOC removal increased with increasing empty-bed contact times in the tested range of filtration velocities (6-18 m/h). Data showed that it was necessary to double the empty-bed contact time when temperature decreased from 20 degree C to 8 degree C to keep a similar BDOC removal efficiency, although the average bacterial biomass was the same at both temperatures.