Biofilter response to gradual and sudden variations in operating conditions

Biefiltration 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 (H2S) 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,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 biotilters 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 H2S feeding rate was gradually decreased from 0.55 to 0.26 g m(-3). (C) 2004 Elsevier B.V. All rights reserved.