微生物烟气脱硫技术是利用化能自养微生物对 SOx 的代谢过程, 将烟气中的硫氧化物脱除。在微生物脱硫过程中, 氧化态的污染物如SO2、硫酸盐、亚硫酸盐及硫代硫酸盐经过微生物的还原作用生成单质硫而被去除。目前研究认为有2 种方式: 一是同化型硫酸盐还原作用, 利用微生物把硫酸盐还原成还原态的硫化物, 然后再固定到蛋白质中; 另一种是异化型硫酸盐还原作用, 是在厌氧条件下将硫酸盐还原成硫化氢的过程。典型的脱硫细菌有排硫硫杆菌( Thiobacillus thioparus) 、氧化亚铁硫杆菌 ( Thiobacillus ferrooxidans) 、脱氮硫杆菌( Thiobacillus denitrificans ) 、脱硫弧菌属( Desulfovibrio) 、贝氏硫菌属( Beggiatoa) 、辫硫菌属( Thioploca) 、发硫菌属 ( Thiothrix) 、紫色硫细菌( Chromatiaceae) 、绿色硫细菌(Chlorobiaceae) 等。寻找可用于燃煤烟气脱硫的微生物菌种、了解其代谢途径、提高脱硫效率是生物烟气脱硫研究的关键。成功地分离出一株无机化能自养型的脱氮硫杆菌( Thiobacillus denitrificans) , 该菌在pH 值为2.0～3.0 的条件下有较好的脱硫性能和潜力, 不仅可以利用硫代硫酸盐作为能源, 而且可以利用硫酸盐作为唯一的硫源进行生长, 为进一步开发烟气的微生物脱硫技术提供依据。
Microbial flue gas desulfurization technology is to remove sulfur oxides from flue gas by utilizing the metabolic process of chemical energy autotrophic microorganisms to SOx. In the process of microbial desulfurization, oxidized pollutants such as SO2, sulfate, sulfite and thiosulfate are removed by the reduction of microorganisms to form elemental sulfur. At present, there are two ways: one is assimilative sulfate reduction, which uses microorganisms to reduce sulfate to reduced sulfide, and then fix it into protein; The other is dissimilatory sulfate reduction, which is the process of reducing sulfate to hydrogen sulfide under anaerobic conditions. Typical desulfurization bacteria include Thiobacillus thiobacillus, Thiobacillus ferrooxidans, Thiobacillus denitrificans, Desulfovibrio, Beggiatoa, Thioploca, Thiothrix, Chromatiaceae, and Chlorobiaceae. The key to the research of biological flue gas desulfurization is to find microbial strains that can be used for flue gas desulfurization, understand their metabolic pathways and improve the desulfurization efficiency. A strain of inorganic autotrophic Thiobacillus denitrificans has been successfully isolated, which has good desulfurization performance and potential under the condition of pH 2.0~3.0. It can not only use thiosulfate as energy, but also use sulfate as the only sulfur source for growth, providing a basis for further development of microbial desulfurization technology of flue gas.
将分离得到的一株氧化亚铁硫杆菌用海藻酸钠进行固定化包埋试验, 用上柱通气法测定其净化气相SO2 的能力, 其氧化降解SO2 的效率高达97.01%, 显示了利用固定化细菌净化低浓度SO2 烟气的可行性。文献[ 3] 在实验室条件下, 选用氧化亚铁硫杆菌进行了烟气脱硫研究, 实验表明, 在适宜的液气比( 12.5 L/m3 以上) 、二氧化硫体积分数〔( 1 000～5 000) ×10- 6〕和三价铁离子质量浓度( 0.6 g/L 以上) 下, 该菌的脱硫率达到98%。
An isolated strain of Thiobacillus ferrooxidans was immobilized with sodium alginate for embedding test. Its ability to purify SO2 in the gas phase was determined by up-column aeration method. Its efficiency of oxidative degradation of SO2 was up to 97.01%, indicating the feasibility of using immobilized bacteria to purify low concentration SO2 flue gas. Literature [3] Under laboratory conditions, Thiobacillus ferrooxidans was selected to conduct flue gas desulfurization research. The experiment showed that at the appropriate liquid-gas ratio (above 12.5 L/m3), sulfur dioxide volume fraction [(1000~5000) × Under the mass concentration of 10-6] and trivalent iron ion (more than 0.6 g/L), the desulfurization rate of the bacteria reached 98%.
对氧化亚铁硫杆菌的固定化技术进行研究, 采用H- 2 软性填料作为载体, 亚铁离子的转换率可保持在95%左右, 脱硫率可达到 98.87%。
The immobilization technology of Thiobacillus ferrooxidans was studied. Using H-2 soft filler as carrier, the conversion rate of ferrous ion could be maintained at about 95%, and the desulfurization rate could reach 98.87%.
氧化亚铁硫杆菌因其独特的生理性质在烟气脱硫等领域具有潜在的巨大应用价值, 但其生长速率缓慢是不利的因素, 必须增强对该菌能量再生机制的理解。由于分子生物学技术的应用, 氧化亚铁硫杆菌铁氧化系统中的绝大多数功能成分已得到了鉴定。目前认为从Fe2+到O2 的电子传递链主要包括: 亚铁氧化还原酶→铁质兰素→至少1 种细胞色素 c→a1 型细胞色素氧化酶等。而从Fe2+到NAD( P) +的反向电子传递链则可能通过一种由细胞色素bc1 复合体参与的反向Q- 循环机制来传递电子[5]。相对铁氧化系统而言, 硫的氧化研究则进展较慢, 目前关于元素硫的氧化已证实存在2 种机制: ( 1) 在硫基础盐培养基中有氧生长时硫氧化以氧为终电子受体; ( 2) 在铁基础盐培养基中厌氧生长时, 利用3 个酶即硫化氢- Fe3+氧化还原酶, 亚硫酸- Fe3+氧化还原酶及铁( Ⅱ) 氧化酶, 共同将元素硫氧化成硫酸[6]。
Thiobacillus ferrooxidans has great potential application value in the field of flue gas desulfurization due to its unique physiological properties, but its slow growth rate is an adverse factor, so it is necessary to enhance the understanding of its energy regeneration mechanism. Due to the application of molecular biological technology, most of the functional components in the iron oxidation system of Thiobacillus ferrooxidans have been identified. At present, it is believed that the electron transfer chain from Fe2+to O2 mainly includes: ferrous oxidoreductase → ferricyanin → at least one kind of cytochrome c → a1 type of cytochrome oxidase, etc. The reverse electron transfer chain from Fe2+to NAD (P)+may transfer electrons through a reverse Q-cycle mechanism involving the cytochrome bc1 complex [5]. Compared with the iron oxidation system, the research of sulfur oxidation is relatively slow. At present, the oxidation of elemental sulfur has been confirmed to have two mechanisms: (1) oxygen is the final electron acceptor of sulfur oxidation when it grows in the sulfur base salt medium; (2) During anaerobic growth in iron base salt medium, three enzymes, namely hydrogen sulfide - Fe3+oxidoreductase, sulfite - Fe3+oxidoreductase and iron (II) oxidase, are used to jointly oxidize elemental sulfur into sulfuric acid [6].
2.2 SO2 转化为SO4 2- 工艺过渡金属Fe3+离子对S( Ⅳ) 的催化氧化和吸收作用已被前人证实。而该反应是一个Fe3+离子递减、 Fe2+离子递增的过程, 随着反应的进行, SO2 的催化氧化和吸收速度受Fe3+离子的减少和老化进程所控制, 进而失去脱硫作用, 故需大量空气氧化Fe2+离子以保证Fe3+离子的浓度和活性。在酸性条件下, 空气氧化Fe3+离子的速度较慢。而自然界中一些微生物如氧化硫硫杆菌和氧化亚铁硫杆菌等具有在酸性条件下快速氧化Fe2+离子为Fe3+离子和SO3 2- 为SO4 2- 的能力, 可以用微生物和铁离子体系共同催化氧化及吸收SO2。
2.2 The catalytic oxidation and absorption of S (Ⅳ) by the transition metal Fe3+ions in the process of converting SO2 to SO42 has been confirmed by previous researchers. The reaction is a process of Fe3+ion decreasing and Fe2+ion increasing. As the reaction proceeds, the catalytic oxidation and absorption rate of SO2 are controlled by the reduction and aging process of Fe3+ion, and thus the desulfurization effect is lost. Therefore, a large amount of air is required to oxidize Fe2+ion to ensure the concentration and activity of Fe3+ion. Under acidic conditions, air oxidation of Fe3+ions is slow. However, some microorganisms in nature, such as Thiobacillus thiooxidans and Thiobacillus ferrooxidans, have the ability to rapidly oxidize Fe2+ions to Fe3+ions and SO32 - to SO42 - under acidic conditions, and can use microorganisms and iron ion systems to jointly catalyze the oxidation and absorption of SO2.
使用的微生物为单种或多种无机化能自养型细菌, 在简单无机盐培养基中生长, 不需昂贵的有机成分, 依靠氧化Fe2+离子和SO3 2- 离子获取能量生长, 烟气中的O2、CO2 和矿质盐适合细菌生长, 并且细菌能适应高浓度的重金属离子和灰分。SO2 脱除后生成稀硫酸及其盐, 可根据当地资源特点生产硫酸盐产品, 如硫酸亚铁、硫酸铁、聚合硫酸铁等产品。文献[ 7] 用分离所得的氧化亚铁硫杆菌和铁离子体系处理含SO2 气体的试验研究, 结果表明, 细菌菌液比稀硫酸吸收法的脱硫效率更高。脱硫效果由细菌本身和溶液中Fe3+的共同作用所决定, 脱硫效率受Fe3+浓度、气液比和进气SO2 的浓度等条件的影响, 当Fe3+质量浓度大于0.6 g/L 时脱硫效率较高。
The microorganisms used are single or multiple inorganic autotrophic bacteria, which grow in a simple inorganic salt medium without expensive organic components. They rely on oxidized Fe2+ions and SO32 - ions to obtain energy for growth. The O2, CO2 and mineral salts in the flue gas are suitable for bacterial growth, and the bacteria can adapt to high concentrations of heavy metal ions and ash. After SO2 removal, dilute sulfuric acid and its salts can be generated, and sulfate products can be produced according to the characteristics of local resources, such as ferrous sulfate, ferric sulfate, polymeric ferric sulfate and other products. The experimental study on the treatment of SO2 containing gas with the isolated Thiobacillus ferrooxidans and iron ion system in literature [7] shows that the desulfurization efficiency of the bacterial liquid is higher than that of the dilute sulfuric acid absorption method. The desulfurization effect is determined by the joint action of the bacteria and Fe3+in the solution. The desulfurization efficiency is affected by the conditions such as Fe3+concentration, gas-liquid ratio and inlet SO2 concentration. When the mass concentration of Fe3+is greater than 0.6 g/L, the desulfurization efficiency is higher.
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