Performance and substance transformation of low-pH and neutral-pH biofilters treating complex gases containing hydrogen sulfide, ammonia, acetic acid, and toluene

Two biofilters with low pH and neutral pH were operated on pilot scale for the treatment of complex gases containing hydrogen sulfide, ammonia, acetic acid, and toluene during 205 days. Under the coexistence of complex gases, the low-pH biofilter (LPB) had higher removal efficiency (RE) for hydrogen sulfide and toluene, and the maximum efficiencies were 99.24% and 99.90% respectively, while the neutral-pH biofilter (NPB) had higher REs of ammonia and acetic acid, up to 99.90% and 99.92% respectively. Higher pressure drop up to 622 Pa was achieved in the LPB, most likely caused by the special structure of fungi different from bacteria. Determination of the concentration of carbon-based intermediates revealed the dominant microbial removal of acetic acid and clarified the relationship between the generation of intermediate and the performance of biofilters. Respective amount of CO₂ in the inlet and outlet showed that the mineralization capacity of the NPB was higher than that of the LPB, and it was more influenced by empty bed residence time (EBRT). The proportion of different forms of nitrogen and sulfur in the filler indicated that the removal of ammonia in the LPB mainly depended on the adsorption by moisture, while that in the NPB was microbial degradation, which was also the main removal pathway of sulfur regardless of pH condition. The removal and transformation of different substances in coexisting complex gases showed different characteristics in the LPB and NPB respectively.