微生物煙氣脫硫技術(shù)是利用化能自養(yǎng)微生物對 SOx 的代謝過程, 將煙氣中的硫氧化物脫除。在微生物脫硫過程中, 氧化態(tài)的污染物如SO2、硫酸鹽、亞硫酸鹽及硫代硫酸鹽經(jīng)過微生物的還原作用生成單質(zhì)硫而被去除。目前研究認(rèn)為有2 種方式: 一是同化型硫酸鹽還原作用, 利用微生物把硫酸鹽還原成還原態(tài)的硫化物, 然后再固定到蛋白質(zhì)中; 另一種是異化型硫酸鹽還原作用, 是在厭氧條件下將硫酸鹽還原成硫化氫的過程。典型的脫硫細(xì)菌有排硫硫桿菌( Thiobacillus thioparus) 、氧化亞鐵硫桿菌 ( Thiobacillus ferrooxidans) 、脫氮硫桿菌( Thiobacillus denitrificans ) 、脫硫弧菌屬( Desulfovibrio) 、貝氏硫菌屬( Beggiatoa) 、辮硫菌屬( Thioploca) 、發(fā)硫菌屬 ( Thiothrix) 、紫色硫細(xì)菌( Chromatiaceae) 、綠色硫細(xì)菌(Chlorobiaceae) 等。尋找可用于燃煤煙氣脫硫的微生物菌種、了解其代謝途徑、提高脫硫效率是生物煙氣脫硫研究的關(guān)鍵。成功地分離出一株無機(jī)化能自養(yǎng)型的脫氮硫桿菌( Thiobacillus denitrificans) , 該菌在pH 值為2.0～3.0 的條件下有較好的脫硫性能和潛力, 不僅可以利用硫代硫酸鹽作為能源, 而且可以利用硫酸鹽作為的硫源進(jìn)行生長, 為進(jìn)一步開發(fā)煙氣的微生物脫硫技術(shù)提供依據(jù)。
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.
將分離得到的一株氧化亞鐵硫桿菌用海藻酸鈉進(jìn)行固定化包埋試驗(yàn), 用上柱通氣法測定其凈化氣相SO2 的能力, 其氧化降解SO2 的效率高達(dá)97.01%, 顯示了利用固定化細(xì)菌凈化低濃度SO2 煙氣的可行性。文獻(xiàn)[ 3] 在實(shí)驗(yàn)室條件下, 選用氧化亞鐵硫桿菌進(jìn)行了煙氣脫硫研究, 實(shí)驗(yàn)表明, 在適宜的液氣比( 12.5 L/m3 以上) 、二氧化硫體積分?jǐn)?shù)〔( 1 000～5 000) ×10- 6〕和三價(jià)鐵離子質(zhì)量濃度( 0.6 g/L 以上) 下, 該菌的脫硫率達(dá)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%.
對氧化亞鐵硫桿菌的固定化技術(shù)進(jìn)行研究, 采用H- 2 軟性填料作為載體, 亞鐵離子的轉(zhuǎn)換率可保持在95%左右, 脫硫率可達(dá)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%.
氧化亞鐵硫桿菌因其獨(dú)特的生理性質(zhì)在煙氣脫硫等領(lǐng)域具有潛在的巨大應(yīng)用價(jià)值, 但其生長速率緩慢是不利的因素, 必須增強(qiáng)對該菌能量再生機(jī)制的理解。由于分子生物學(xué)技術(shù)的應(yīng)用, 氧化亞鐵硫桿菌鐵氧化系統(tǒng)中的絕大多數(shù)功能成分已得到了鑒定。目前認(rèn)為從Fe2+到O2 的電子傳遞鏈主要包括: 亞鐵氧化還原酶→鐵質(zhì)蘭素→少1 種細(xì)胞色素 c→a1 型細(xì)胞色素氧化酶等。而從Fe2+到NAD( P) +的反向電子傳遞鏈則可能通過一種由細(xì)胞色素bc1 復(fù)合體參與的反向Q- 循環(huán)機(jī)制來傳遞電子[5]。相對鐵氧化系統(tǒng)而言, 硫的氧化研究則進(jìn)展較慢, 目前關(guān)于元素硫的氧化已證實(shí)存在2 種機(jī)制: ( 1) 在硫基礎(chǔ)鹽培養(yǎng)基中有氧生長時(shí)硫氧化以氧為終電子受體; ( 2) 在鐵基礎(chǔ)鹽培養(yǎng)基中厭氧生長時(shí), 利用3 個(gè)酶即硫化氫- Fe3+氧化還原酶, 亞硫酸- Fe3+氧化還原酶及鐵( Ⅱ) 氧化酶, 共同將元素硫氧化成硫酸[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 轉(zhuǎn)化為SO4 2- 工藝過渡金屬Fe3+離子對S( Ⅳ) 的催化氧化和吸收作用已被前人證實(shí)。而該反應(yīng)是一個(gè)Fe3+離子遞減、 Fe2+離子遞增的過程, 隨著反應(yīng)的進(jìn)行, SO2 的催化氧化和吸收速度受Fe3+離子的減少和老化進(jìn)程所控制, 進(jìn)而失去脫硫作用, 故需大量空氣氧化Fe2+離子以保證Fe3+離子的濃度和活性。在酸性條件下, 空氣氧化Fe3+離子的速度較慢。而自然界中一些微生物如氧化硫硫桿菌和氧化亞鐵硫桿菌等具有在酸性條件下快速氧化Fe2+離子為Fe3+離子和SO3 2- 為SO4 2- 的能力, 可以用微生物和鐵離子體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.
使用的微生物為單種或多種無機(jī)化能自養(yǎng)型細(xì)菌, 在簡單無機(jī)鹽培養(yǎng)基中生長, 不需昂貴的有機(jī)成分, 依靠氧化Fe2+離子和SO3 2- 離子獲取能量生長, 煙氣中的O2、CO2 和礦質(zhì)鹽適合細(xì)菌生長, 并且細(xì)菌能適應(yīng)高濃度的重金屬離子和灰分。SO2 脫除后生成稀硫酸及其鹽, 可根據(jù)當(dāng)?shù)刭Y源特點(diǎn)生產(chǎn)硫酸鹽產(chǎn)品, 如硫酸亞鐵、硫酸鐵、聚合硫酸鐵等產(chǎn)品。文獻(xiàn)[ 7] 用分離所得的氧化亞鐵硫桿菌和鐵離子體系處理含SO2 氣體的試驗(yàn)研究, 結(jié)果表明, 細(xì)菌菌液比稀硫酸吸收法的脫硫效率更高。脫硫效果由細(xì)菌本身和溶液中Fe3+的共同作用所決定, 脫硫效率受Fe3+濃度、氣液比和進(jìn)氣SO2 的濃度等條件的影響, 當(dāng)Fe3+質(zhì)量濃度大于0.6 g/L 時(shí)脫硫效率較高。
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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