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 S2O32--S L-1 and 0.2-0.58 g NO2 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 S2O32--S. Based on Monod model, the maximum substrate utilisation rate (qm) was 0.024 h-1 with half saturation constant (Ks) 0.42 g S2O32--S L-1 at initial [S2O32--S] of 14 g L-1. S0 accumulated at [S2O32--S] ≥ 1.5 g L-1 (10% yield at initial 9.5 g S2O32--S L-1) and the highest S0 yield estimated with the model was 61% with initial [S2O32--S] of 16.5 g L-1. Anoxically, the maximum nitrite removal rate based on Monod modelling was 0.011 h-1 with Ks = 0.84 g NO2- L-1. Aerobically and anoxically the maximum specific growth rates (µm) 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 S0 accumulated under anoxic conditions. Thus, future developments of biotechnical applications for the recovery of S0 from haloalkaline streams from the process industry should focus on aerobic treatment.HighlightsHaloalkaline S2O32- biotransformations kinetics by Thioalkalivibrio denitrificansAerobic thiosulphate-S bioconversion up to 0.024 h-1 with Ks = 0.42 g S2O32--S L-110% S0 yield with initial 9.5 g S2O32--S L-1 in aerobic conditionAnoxic NO2 removal up to 0.01 h-1 with Ks = 0.84 g NO2- L-1.

Increase in sedimentary organic carbon with a change from hypoxic to oxic conditions.

In the Seto Inland Sea, Japan, chemical oxygen demand has increased over recent decades, while average dissolved oxygen concentrations in the bottom water have increased. In this study, we investigated responses of organic carbon (OC) in hypoxic sediment to changes of redox conditions using experimental columns containing sediment and overlying water. Surface sediment showed an increase in OC along with the change to an aerobic condition. Microbial community analysis showed a predominance of sulfur-oxidizing bacteria (SOB) such as Sulfurovum sp. in the sediment. This dominance could account for the increased OC. Additionally, the dissolved organic carbon (DOC) concentration in the overlying water increased. Further experiments using sandy sediment showed that biodegradation of Sulfurimonas denitrificans was associated with DOC release. These results show that a change in the sedimentary environment (increase in dissolved oxygen) increased the sedimentary OC and DOC of overlying water by stimulating certain autotrophic bacteria, especially the SOB.