Operation of Biofilter with Mixed Agricultural Residue as Filter Material: Effects of Humidification and Inlet Hydrogen Sulfide Volume fraction on the Performance

A. Gangagni Rao, P. Ravichandra and A. Jetty

Abstract
Mixed agricultural residue, inoculated with aerobic sulfide oxidizing microbial consortium, was used as biofilter media to study the removal efficiency (ηR) of hydrogen sulfide (H2S). The effect of humidification and inlet H2S volume fraction on the performance of biofilter was also investigated. A 3.9 l bench scale biofilter was continuously operated to treat air containing H2S gas in the range of φ = 275 to 2833 · 10–6 for 150 days. ηR of 99 % was obtained at φ = 2020 · 10–6 of inlet H2S volume fraction during continuous operation with humidification. However, η,R dropped to 51 % when the inlet H2S fraction increased beyond φ = 2020 · 10–6. A maximum elimination productivity of 91 g m–3 H2S of filter bed h-1 and inlet mass loading rate of 91 g m-3 H2S of filter bed h-1 was achieved when the tEBRT was in the range of 15 – 155 s. The filter was operated without the humidifier at the inlet H2S fraction of φ = 2020 · 10–6 and observed that ηR dropped to 51 % due to the drop in moisture of the filter material. However, ηR could be recovered up to 83 % upon reintroduction of humidifier into the circuit of biofiltration process indicating, that humidification of the waste gas was essential to achieve the highest possible ηR at particular inlet H2S fraction. The filter recorded ηR above 99 % even in the acidic phase at φ = 2020 ·10–6 of inlet H2S fraction without intermittent washing. The gas dispersion characteristics were comparable to the previously tested bed materials, offering low-pressure drop across the biofilter in the range of 21 – 74mm of H2O per meter height of packing material.

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Keywords
biofiltration, mixed agriculture waste, H2S, moisture, humidifier, pressure drop, sulfur oxidizing bacteria