Understanding the limits of H2S degrading biotrickling filters using a differential biotrickling filter

The removal of H2S in high performance biotrickling filters was investigated using a differential biotrickling filter. The differential biotrickling filter was designed to reach high gas velocities through a minature packed bed, in this case a single 4-cm open-pore polyurethane foam cube. External mass transfer was limiting below air velocities of 3000-4000 m h−1, with possible other parameters such as biological kinetics or diffusion-controlled performance above 4000 m h−1. The effect of the liquid trickling rate on H2S elimination was found to be nil at low gas velocity, and significant at high gas velocity, consistent with speculations on the wetting of the packing and the rate-limiting step at the conditions of the experiments. The effect of additions of various species of sulfur on H2S treatment was investigated. Sulfide negatively affected H2S removal, while sulfate and sulfite had no effect. Interestingly, traces of thiosulfate resulted in improved H2S removal rates. Cell activity assessed by oxygen-uptake rate determinations was the greatest at near neutral pH. Finally, biokinetic parameters for H2S elimination obtained in the differential biotrickling filter and in a batch suspended culture were compared. The rates in the differential biotrickling filter were much higher, indicating that the batch reactor was subject to mass transfer limitation, and illustrating that the biokinetic parameters determined in shake flask systems may not necessarily apply in biotrickling filters. Overall, the study highlights that a differential biotrickling filter is a useful tool for investigating the performance and limits of H2S biotrickling filtration, and that detailed studies help in understanding the mechanisms of pollutant removal in biotrickling filters.