Comparison of the biological NH3 removal characteristics of a three stage biofilter with a one stage biofilter
A three stage and a one-stage bench-scale biofilter with effective heights of 129 cm filled with same type of packing material were operated at different influent concentrations of ammonia in order to investigate their performance in treating waste gas streams. The columns contained a mixture of municipal compost inoculated with thickened municipal activated sludge as a base material and shredded hard plastic as a bulking agent in a 3:2 v/v ratio; the porosity, density and pH were 52 %, 0.65 and 7.2 respectively. Microbial acclimation to ammonia was achieved by exposing the three stage biofilter to an average inlet loading rate of 2.15g-NH3/m3 h and the one-stage to an average inlet loading rate of 1.32 g NH3/m3 h and an empty bed residence time of 60 s, for 10 days and 17 days respectively. Under steady-state condition, maximum elimination capacity (EC) was 9.85 g-NH3/m3h at a loading rate of 9.86 g-NH3/m3h for three-stage biofilter and 8.08 g NH3/m3h at a loading rate of 8.13 g-NH3/m3h for one-stage biofilter. The average pressure drop across biofilters bed was determined 33.76 Pa/m1 in three-stage biofilter and 180.7 Pa/m1 in one-stage biofilter. The three stage biofilter showed superior performance and gained more elimination capacity, shorter acclimation time, longer operation in steady-state condition and less pressure drop than one-stage biofilter.