Removal of odorous sulphur compounds from industrial gases by biotrickling filters

A pilot plant for the removal of odorous sulphur gases was established at an industrial phosphoric acid production plant line located in Skhira (Tunisia). The air pollution control system train consists of a first stage, including a chemical scrubber operating with an alkaline solution containing caustic soda, followed by a two-stage biotrickling filter (BTF) filled with Mytilus edulis shells. In this study the performance of the dual-stage BTF in the removal of hydrogen sulphide (H2S), sulphur dioxide (SO2) and dimethyl sulphide (DMS) contained in the exhaust air current from the phosphoric acid reactor was evaluated. The concentrations of H2S, SO2 and DMS at the inlet of the two-stage BTF were 10-30 ppm, < 1-20 ppm and 16-30 ppm, respectively. All the respective concentrations at the outlet of the biological step were < 1 ppm, except for the H2S in outlet during the first day of operation (10 ppm). Removal efficiencies were generally higher than 95% for all compounds, and remained high even with an increase of the off-gas flow rate. Mass-removal capacity was, at the least, 2.0 g m-3 h-1, 0.5 g m-3 h-1 and 6.2 g m-3 h-1, for H2S, SO2 and DMS, respectively. The process gave satisfying removal efficiencies, especially if considering the already low inlet concentrations, owing to the high quality of raw phosphate used