Biofiltration of air loaded with ammonia by granulated sludge

Abstract Granulated sludge has some physico‐chemical characteristics that make it useful as a packing material in biofilters. The purpose of this study was to investigate the potential of a biofiltration unit packed with this support material to treat ammonia. The results show that ammonia elimination is very high. The maximum removal efficiency at a volumetric load of 140 and 300 g ammonia.m−3 packing.day−1 is 90% and 80%, respectively. The use of sludge requires neither nutritive aqueous solution, nor buffer solution, as was the case for other treatment systems. Subject to adequate humidification, the pressure drops measured were very low. Ammonia was oxidized to nitrite, nitrate, and probably gaseous nitrogen, the proportions of each depending on operating conditions of the biofilter. For ammonia concentrations below 576 g ammonia.m−3 packing.day−1, ammonia removal in biofilters packed with sludge followed apparent first order kinetics. The maximum growth rates estimated by the theoretical model and experimental results are slightly superior to those found for pure cultures. The operating conditions would seem to be more favorable to nitrifying bacteria growth. These results also show the complex phenomena which govern ammonia removal in biofilters.