Elemental sulphur production from thiosulphate under haloalkaline conditions in a Thioalkalivibrio versutus amended fluidized bed bioreactor

Abstract

<p>Concentrated sulphurous and saline streams, produced for example by pulp and paper and petrochemical industries, pose challenges for both environmental and processes management. In this study, the potential of biological recovery of S<sup>0</sup> from haloalkaline thiosulphate solution in a Thioalkalivibrio versutus amended continuous-flow fluidized bed bioreactor (FBBR) was investigated using different (12−5 h) hydraulic retention times (HRT) as well as physico-chemical means to separate the S<sup>0</sup> produced. S<sub>2</sub>O<sub>3</sub><sup>2−</sup> was biotransformed to SO<sub>4</sub><sup>2−</sup> and S<sup>0</sup> with the highest biotransformation efficiency of 99.9 %. At 7 h HRT, the capacity of the FBBR was reached, seen as incomplete thiosulphate conversion. S<sup>0</sup> production rate increased up to 6.3 ± 0.6 g S/l/d at HRT 7 h, whilst the average S<sup>0</sup> yield was 27 ± 2 %. The presence of biologically produced S<sup>0</sup> was visual and identified by scanning electron microscopy. Separation of S<sup>0</sup> from the effluent by centrifugation at 3417 relative centrifugal force (rcf) resulted in 93 % separation, while among the four tested coagulants, FeCl<sub>2</sub> at 0.5 g/l resulted in 40 % separation. Also, FeCl<sub>2</sub> enhanced thiosulphate biotransformation rates. In summary, continuous biological S<sup>0</sup> production followed by separation by centrifugation indicates potential for sulphur recovery from alkaline and saline industrial streams.</p>