Potential of biological sulphur recovery from thiosulphate by haloalkaliphilic Thioalkalivibrio denitrificans

The aim of this study was to investigate the potential for elemental sulphur recovery from sulphurous solutions under aerobic and anoxic conditions by haloalkalophilic Thioalkalivibrio denitrificans at 0.8–19.6 g S ₂O ₃ ²⁻-S L ⁻¹ and 0.2–0.58 g NO ₂ L ⁻¹, respectively. The experiments were conducted as batch assays with haloalkaline (pH 10 and ≥ 14 g Na ⁺ L ⁻¹) thiosulphate solution. Aerobically, the highest biotransformation rate of thiosulphate obtained was 0.03 h ⁻¹ at 8.5 g L S ₂O ₃ ²⁻-S. Based on Monod model, the maximum substrate utilisation rate (q _m) was 0.024 h ⁻¹ with half saturation constant (K _s) 0.42 g S ₂O ₃ ²⁻-S L ⁻¹ at initial [S ₂O ₃ ^2--S] of 14 g L ⁻¹. S ⁰ accumulated at [S ₂O ₃ ²⁻-S] ≥ 1.5 g L ⁻¹ (10% yield at initial 9.5 g S ₂O ₃ ²⁻-S L ⁻¹) and the highest S ⁰ yield estimated with the model was 61% with initial [S ₂O ₃ ^2--S] of 16.5 g L ⁻¹. Anoxically, the maximum nitrite removal rate based on Monod modelling was 0.011 h ⁻¹ with K _s= 0.84 g NO ₂ ⁻ L ⁻¹. Aerobically and anoxically the maximum specific growth rates (µ _m) were 0.046 and 0.022 h ⁻¹, respectively. In summary, high-rate aerobic biotransformation kinetics of thiosulphate were demonstrated, whereas the rates were slower and no S ⁰ accumulated under anoxic conditions. Thus, future developments of biotechnical applications for the recovery of S ⁰ from haloalkaline streams from the process industry should focus on aerobic treatment. Highlights: Haloalkaline S ₂O ₃ ²⁻ biotransformations kinetics by Thioalkalivibrio denitrificans Aerobic thiosulphate-S bioconversion up to 0.024 h ⁻¹ with K _s = 0.42 g S ₂O ₃ ²⁻-S L ⁻¹ 10% S ⁰ yield with initial 9.5 g S ₂O ₃ ^2--S L ⁻¹ in aerobic condition Anoxic NO ₂ removal up to 0.01 h ⁻¹ with K _s = 0.84 g NO ₂ ⁻ L ⁻¹.