Sulfur Oxidizing Bacteria Screening And Basic Research Of Biological Sulfur Removal

The biological desulfurization technology has a promising future, for it already showedsome advantages, such as, rather simple facilities and mild operation conditions needed,safety and lower cost, and producing hardly secondary pollution. However, there are stillsome problems of this technology remained, including lower efficiency of strain and reactor,and rather immaturity of processing techniques.In this study, a sulfur oxidizing bacterium has been isolated, it showed sulfur removalability when being cultivated in sulfide medium. The study was aimed to apply JNU-2in thetwo stages microbial desulfurization process of flue gas SO2absorption solution, and furtherexplore the path and process to convert sulfate into elemental sulfur. The main results are asfollows:A sulfur oxidizing bacterium was isolated from an anaerobic sludge pool. Its16S rRNAsequence was almost same as the spice of Thermithiobacillus tepidarius (T. tepidarius),named T. tepidarius JNU-2. JNU-2was the first reported Thermithiobacillus strain forremoving sulfide and recycling sulfur from simulative sulfate containing waste water. Afterculture conditions optimization (pH6.0,37℃), the thiosulfate removal ratio and elementalsulfur production ratio reached98.0%and83.06%, respectively, after incubating for24hours.Based on the traits of JNU-2, a new-style sulfurs regeneration reactor-Internal AirliftLoop Reactor (IALR) was provided and successfully applied. The key operating conditionsventilatory capacity (VC) and hydraulic retention time (HRT) were also respectivelyinvestigated. The production ratio of elemental sulfur was about60.0%and the maximal yieldwas75mg L-1h-1at60mL min-1VC and10h HRT. All the above results indicated that thestrain JNU-2and the new-style reactor would be of great potential for producing sulfur sourcein industrial site.The sulfide oxidation dynamic model of IALR and JNU-2strain desulfurization systemq1=0.132×10-6S/(0.811+S) and q2=0.092×10-6P0/(2.019+P0) were established and verified. Themodel was consistent with the actual under lower VC (60mL min-1). Compared with theactual value, the difference of simulative S2-oxidation ratio and S0generate ratio were only11.04%and5.41%, respectively, at13h HRT; The same comparisons at10h HRT were only13.15%and3.63%, respectively. The simulation values were significant different from theactual under higher VC (360mL min-1).In order to apply the JNU-2strain in the sulfide oxidation phase of two stages flue gasbiological desulfurization, its previous reaction--sulfate bio-reduction was studied. The SRBanaerobic activated sludge was domesticated with high sulfate concentration, it was utilized for bio-reduction treatment of simulated flue gas SO2absorption liquid.3,780mg L-1sulfatereduction ratio increased more than10%in the appropriate culture condition (pH6.5,32℃,Fe2+2mg L-1). In the sulfate reduction process, the optimum value of ThCOD/SO24-andThCOD (Theoretical chemical oxygen demand) were found of3and3.33, respectively,1,110mg L-1sulfate reduction ratio reached72.15%. The activity of SRB was suppressed by300mg L-1sulfide in the sulfate reduction system. The domesticated SRB anaerobic activatedsludge would be of great industrial potential for flue gas bio-desulfurization.The effects of several common heavy metal ions in the flue gas on SRB sulfate reductionwere analyzed. It was found that the heavy metal ions, Ni2+and Pb2+, showed stronginhibition on SRB sulfate reduction ability at the level of1.0mg L-1and2.0mg L-1,respectively. Meanwhile, Cu2+inhibition detail at rather higher concentration (8.0mg L-1). Itproved that the heavy metal ions which have negative impacts must be removed to ensure theefficient sulfate bio-reduction.The effects of sulfate reduction organic substrate and product on sulfide bio-oxidationwere analyzed. It was found that the sulfate reduction substrate-lactate and bio-conversionproduct-acetate had inhibitory effect on sulfide oxidation, especially, the presence acetatestrongly inhibit the bio-oxidization process (22.88%thiosulfate conversion ratio after beingcultivated84h,1.38%elemental sulfur production ratio after cultivating24h). So the sulfidegenerated from anaerobic reduction reaction should be extracted in order to avoid feedbackinhibition by the reductive product.