| Sulfur and nitrogen containing organic wastewater threatens aquatic environment and human health seriously at high concentration. Biological denitrifying sulfide removal process(DSR) can eliminate organic compounds, sulfide and nitrate contaminants effectively and sulfide can be converted to elemental sulfur for resource recycling through the regulation of process parameters. However, how to achieve long-term stable operation in DSR process and effective recovery of elemental sulfur are the main limitations in engineering application and promotion.This study mainly concentrates on the operation and sulfur recovery of wastewater denitrifying sulfide removal. The effects of up-flow velocity and processing loads were investigated by running anaerobic expanded granular sludge bed reactors(EGSB). The stability and efficiency of the DSR process were further improved by optimizing the process parameters. On the other hand, the characteristics of biological elemental sulfur were studied and a reasonable sulfur recovery method was proposed. The purpose of this study was to provide a theoretical basis for the practical engineering operation, control and sulfur recovery in DSR process.The performance of DSR-EGSB reactors were estimated under different up-flow velocity(2m/h, 3.5m/h and 5m/h), and the results showed that the suitable up-flow velocity was 3.5m/h. In three cases, the contents of elemental sulfur in effluent accounted for 37%, 51% and 54% of the total production,respectively. The ratio of elemental sulfur in effluent could be improved effectively through increasing up-flow velocity in a certain range. Furthermore, the impacts of different C-N-S loadings on DSR process were investigated. The suitable C-N-S loadings for DSR process was 2.22 kg C·m-3·d-1,2.06 kg N·m-3·d-1 and 3.93 kg S·m-3·d-1. The removal of acetate, nitrate and sulfide could reach 95%, 98% and 95%, respectively. Accordingly, the yield of elemental sulfur was greater than 85%. The main reason for the breakdown of DSR process was the accumulation of nitrite in the reactor generated by the inhibition of high sulfide loading on Pseudomonas, Azoarcus, Thauera and other heterotrophic denitrification bacteria.The acid destabilization-inclined plate sedimentation-centrifugation combined method for elemental sulfur recovery was proposed based on the properties of biological sulfur. More than 71% of sulfur recovery for the combined method was obtained under the condition of pH 3-5, the surface hydraulic load of the inclined plate sedimentation tank less than 0.42 m3/(m2·h), and the centrifugal speed greater than 3000 r/min. Additionally, the horizontal decanter centrifuge was recommended as the concentrate dewatering equipment for elemental sulfur product, applied in the demonstration project, according to the experimental results. Crude sulfur product with a purity of 35.6%, an average pore diameter of 16.2 nm and BET specific surface area of 8.4 m2/g was obtained. Meanwhile, the characteristic results indicated that the biological sulfur product had a strong adsorption capacity due to the high specific surface, and the composition contained a abundant of organic compounds. The crude sulfur product can be directly utilized in industry, agriculture and environmental protection, can also be used as a recycling commodity sulfur through the secondary purification and refining. |
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