Biofilter response to gradual and sudden variations in operating conditions

Abstract Biofiltration is an efficient technology that involves passing chemical-laden gases through a moist, porous medium containing active microorganisms. Although this technology is apparently simple, its effectiveness relies on the optimisation of several operating parameters and the selection of a suitable packing or carrier material. In this study, four organic packing materials were tested for biofiltration purposes. The highest removal efficiency for hydrogen sulphide (H 2 S) inlet concentrations ranging from 0.03 to 0.32 g m −3 was achieved when filling the bed with the material based on a mixture of pig manure and sawdust. After selecting this carrier material, the response of the biofilter to gradual and sudden changes in the H 2 S loading rate and gas flow rate was studied. A combination of high contaminant inlet concentrations (0.28 g m −3 ) and high gas flow rates (1.3 m 3  h −1 with a EBRT time lower than 22 s) would require two biofilters in series in order to ensure a contaminant outlet mass loading rate lower than 15 g m −3  h −1 is discharged into the atmosphere. The packing material was able to recover high degradation rates after brief starvation periods, but increasing the gas flow rate from 0.81 to 1.85 m 3  h −1 rendered a decreasing elimination capacity (a subsequent increase in non-degraded outlet amounts of contaminant), even when H 2 S feeding rate was gradually decreased from 0.55 to 0.26 g m −3 .