A laboratory-scale biofilter filled with granular sludge(digested and dried) has been used to remove hydrogen sulfide (H2S) and also ammonia (NH3). The biofilter has been effective in removing 96% of the H2S for inlet concentration of less than 230 mg H2S/m3 with no acclimation period and immediate reduction. For the NH3, for concentration of less than 115 mg/m3, a reduction of 72% was measured but an acclimation period of about 6 to 7 weeks was necessary after the nitrifying bacteria seeding to obtain this level of reduction. Changes of the inlet gas concentration affected more the nitrifying bacteria than the sulfur bacteria as their counts showed.

The tests were done to verify the reduction of the concentration of only 2 gases and no link has been done to the verify the effect of these reductions to the final odor of the gas treated. No comment on the a large scale biofilter feasibility is done probably because of the performances of the nitrifying bacteria and the possible need of more experimentation to better understand their behavior.