| Alkali absorption-biological flue gas desulphurization technology includes absorbtion SO2 in flue gas to SO32-/SO42- by sodium hydroxide, anaerobic reduction of SO42- to S2- by the anaerobe and aerobic oxidation of S2- to sulfur element (S0) by the aerobium. In that case, the recovery of sulfur resources are achieved. This paper concentrated on the bio-process and investigated the start-up and running of the aerobic reactor, the tandem and process optimization of the anaerobic and aerobic reactors and the analysis of the sulfur product.The biological oxidation process of sulfide to sulfur with colorless sulfur bacteria was studied in an aerobic internal circulating bio-fluidized bed reactor (effective volume=45L) with the simulation sulfide -containing wastewater as influent. The reactor was started at 30±2℃temperature and 7.00～7.50 of pH and COD:N:P=100:5:1 for the influent. After 28 days, there were a large amount of myceliums in the reactor, and the organic loading rate reached over 3.73kgCOD·m-3·d-1and 1.09kgS2-·m-3·d-1 for the sulfide loading rate. The removal efficiency of organic and sulfide were more than 70 %and 85% respectively while the theoretical yield of sulfur was 75% approximately. In addition, hydraulic retention time (HRT) and the air aeration quantity were inspected. It was demonstrated that the optimum HRT value was 8h under the influent concentration of S2- and organic respectively for 200mg·L-1 and 800mg·L-1, and the best treatment effect of aeration was obtained at 60～90L·h-1.The anaerobic and aerobic reactors were tandemed in the way of using the anaerobic enfluent as aerobic influent under the condition of 30±2℃in two reactors and 7.50～8.50 of pH and COD:N:P=100:5:1 for the anaerobic influent. During 19～30 days, the organic and the SO42- loading rates of anaerobic reactor respectively reached 5.8±0.1kgCOD·m-3·d-1 and 1.8±0.1kgSO42-·m-3·d-1 with 91.2% of the removal efficiency of organic and 85.8% of the SO42- while the theoretical yield of sulfur was 63.9% on average. Furthermore, there were a large amount of myceliums in both reactor, and the aerobic bacteria was not polluted by anaerobic. The water quantity and quality shock lading experiment and the second start-up experiment were operated to observe the run efficiency of the anaerobic-aerobic tandem system. The result showed that the system was good at anti-shocking and resume.On the base of steady running of the anaerobic-aerobic tandem system, Response surface methodology was employed to decide the reciprocal influence of three main factors and to determinate the optimum operation conditions which were calculated from the simulation equation for S0 conversion at HRT of 16h, inlet SO42- concentration of 1348 mg·L-1 and air flow of 165 L·h-1. Statistical test showed that all three factors were significant and the interaction effect of HRT and inlet SO42- concentration was more remarkable than others. The results of demonstration test for 5 days, acquiring theoretical S0 yield efficiency of 65.2% on average which extremely approximate with the predicting value, illustrated that the equation had good applicability with the reactor system.Moreover, the light microscopic photographs of the effluent from aerobic reactor showed that there were lots of sulfur granules and membranaceous sulfur in effluent water. The observation of scanning electron microscope of sulfur product showed that the product was consisted of irregular crystal grains forming into larger particles. It is inferred that the sulfur product was present in the form of rhombic sulfur (a-sulfur) by X-Ray Diffraction analysis. The component and contents were mensurated and it is testified that the purity of sulfur product was 79% approximately. |
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