Treatment of tetrathionate effluents by continuous oxidation in a flooded packed-bed bioreactor

Thiosalts are compounds commonly present in process plant liquor for the concentration of metal sulphide ores by milling and flotation. Since thiosalts are metastable species that are oxidized to sulphuric acid as an end product, they cannot be discharged nor recycled into the process. Therefore, the development of a cost-effective process for the treatment of these effluents is necessary. In this paper, the continuous bio-oxidation of tetrathionate is carried out in a flooded packed-bed reactor by an immobilized microbial consortium. Batch tests show that the initial tetrathionate concentration and pH slightly affect the tetrathionate bio-oxidation process in the ranges 3 to 5 g/L and 1.5 to 2, respectively. The specific bio-oxidation rate is 0.08 h− 1. Only sulphate ions and protons have been detected as end products. For the starting up of the bioreactor, a new method of biofilm formation for tetrathionate bio-oxidation is implemented. The maximum bio-oxidation rate in continuous operation is 0.415 gh− 1 (0.830 kg h− 1 m− 3). The biofilm was stable for the whole period studied, i.e. 35 days. These results indicate that a flooded packed-bed reactor is an interesting option from an economic point of view for the treatment of waters contaminated by thiosalts.