| With the rapid development of industry,China is not only a major emitter of sulfur dioxide,but also a major importer of sulfur.Calcium desulfurization and ammonia desulfurization are widely used in traditional flue gas desulfurization processes.Desulfurization gypsum produced by calcium method lacks resource utilization value due to heavy metals,and it takes up a lot of land;ammonia desulfurization is due to higher liquid ammonia price,the operating cost is high.And the high volatility of liquid ammonia leads to the escape of ammonia,which increases the formation of ash.Sulfate-Reducing Bacteria?SRB?can reduce sulfite and sulfate to sulfide,thereby forming a part of the geochemical cycle of sulfur.Based on the characteristics of SRB to sulfite reduction,the current biological desulfurization of flue gas is mainly the Bio-FGD process in the Netherlands.However,due to the large consumption of alkaline materials in the absorption process,the double bioreactor causes the system to be complicated,and the mutual inhibition of multiple strains and so on,which limits its further application.The research proposed that,firstly,the sulfur-containing flue gas was rinsed to remove dust and inorganic salt components to obtain the sulfite elution absorption solution;started the SRB bioreactor and added the sulfur source?only for the start-up phase of the reactor?to produce S2-via high-efficiency biocatalytic reduction.Then,the S2-in the biochemical treatment effluent was mixed with the SO32-in the leaching absorption solution,and the treated effluent containing the biological sulfur was obtained by a redox-based neutralization reaction,the process mechanism and optimization conditions for the manufacture of sulfur were clarified.Finally,through the study of the morphological size,surface properties?Zeta potential,contact angle,surface tension,etc.?and particle size control of biological sulfur,flue gas desulfurization and sulfur recovery were realized by efficient and low-cost solid-liquid separation method?The solid-liquid separation solution was partially refluxed for leaching absorption of sulfur-containing flue gas,and partially refluxed to the SRB bioreactor for use as the sole source of electron acceptors?.?1?In the biochemical system in which SRB biochemical effluent reacted with SO2 solution,sulfur yield was the highest when pH=4.04±0.10,ORP=-134±17mV,and the maximum sulfur yield was 42.4%.The SO2?aq?-S2-?aq?system showed that pH=3.99±0.21,ORP=-159±40 mV,and SO32-/S2-molar ratio of 1:1 were the best conditions for sulfur production;the sulfur-producing reaction of S2O32-with S2-was a side reaction of the SO2?aq?-S2-?aq?reaction system,which promoted the formation of sulfur.In the later stage of biochemical system and SO2?aq?-S2-?aq?system,the reduction of sulfur production under near-neutral conditions was attributed to the formation of polysulfide and polysulfate.The solid products of the biochemical system and the SO2?aq?-S2-?aq?system were mainly spherical by SEM observation,the EDS and XRD analysis showed that the solid particles were sulfur,and its purity was high;the sulfur produced by the biochemical system was adhered by the extracellular polymer.The results of strain identification indicated that Desulfovibrio was the dominant genus in the SRB biochemical reactor?accounting for65%?.?2?The presence of extracellular macromolecules such as extracellular polymers increased the steric hindrance between the biological sulfur particles and limited the further growth of the sulfur crystals,resulting in a smaller particle size of the biological sulfur than the chemical sulfur.Compared with chemical sulfur,the surface modification of biomacromolecules narrowed the particle size distribution of biological sulfur,which caused biological sulfur to exhibit hydrophilicity different from chemical sulfur,the reduction of surface tension of biochemical system was also an important factor limiting the growth of biological sulfur.Due to its high zeta potential,biological sulfur had good stability in the reaction system,resulting in poor sedimentation performance.The results showed that both reaction temperature and stirring intensity were important factors affecting the growth of biological sulfur.The particle size control of biological sulfur could be achieved by adjusting the reaction temperature and stirring intensity during the reaction.?3?Both the centrifugal separation method and the flocculation precipitation method could effectively separate the biological sulfur products.The electrode method was also feasible for the separation of biological sulfur.In the process of separating biological sulfur by centrifugal separation and electrode method,power consumption was a factor that must be considered.In the centrifugal separation method,the recovery rate of biological sulfur could reach up to 99.65%;in the flocculation precipitation method,when the amount of polyaluminum chloride added was 30.0 mg,the recovery rate of biological sulfur was the highest,which was97.12%.At this time,the zeta potential of the system was close to 0,indicating that the addition of polyaluminum chloride changed the Zeta potential of the system,further affecting the sedimentation performance of biological sulfur.In the electrode method,when the applied voltage was 30 V,the separation efficiency of biological sulfur was the best,and the recovery rate was 74.89%.However,from the perspective of biological sulfur recovery,the electrode method was not an ideal method for separating biological sulfur.Compared with the flocculation sedimentation method,the centrifugal separation method had higher separation efficiency and lower cost for the biological sulfur product,and avoided further treatment of the separated product.It was an ideal separation method for separating biological sulfur at laboratory scale. |
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