Study On Removing Low Concentration SO₂ From Flue Gas By Immobilization Technology Of Microorganism

A new removeal low concentration SO2 technology which aim at the low congcentration dioxide sulfurs (SO2) gas in the coal burning, metal smelting, producing sulfuric acid from gas in metallurgy and other SO2 gas of no recovery worth was study basis immobilization microorganism technology in this thesis. The research focused the domestication of desulfuration bacterium, the technology of preparation immobilization microorganism,16s rRNA sequencing of the desulfuration bacterium, and the operation conditionand, the desulfuration mechanism and dynamics model of removing low concentration SO2 in the fixed bed reactor filled immobilized desulfuration bacterium. The results are as follows:An.dominant desulfuration bacterium, which are a quick growth and propagate in a wide activation temperature and acidic condition, high activation and efficiency for removing SO2, were obtained from the oxidation ditch in city waste water treatment plant after inducement domestication by contained SO2 gas four or five day with 17.5ml (NaNO3 and KH2PO42- etc)/L(bacterium liquid) for nutriment of microorganism, at 0.1m3/h of aeration air,30min of aeration time and stop 60min. The dominant desulfuration bacterium can get their sulfur source with the thiosulfate, sulfite, sulfate, and can growth only with SO2. The reaction rate of the desulfuration bacterium degrades SO32- in aqueous solution accord with M-M equation, where the max reaction rate (rmax)=95818mg/L.h, and M-constant (Km)=36364mg/L. The pH value and temperature of system have evident effect to the degradation rate, and the maximal degradation rate is (1440mg/L.h) at pH=3, T=30℃. The degradation kinetics for SO32- is first order reaction under 30"C of the system temperature, and the reaction rate constant is k= 6.522×l08exp(-5902/T), the activation energy is=49.07kJ/mol.The desulfuration bacterium were studied using molecular biology based on 16S rRNA sequence comparison, and the results of the conformation or function of microbial communities with in situ hybridization and in situ PCR were exhibited. There are 8 dominant desulfuration bacterium to be found and they occupy about 70%of all microorganism. Tow phylogenetic trees were got because there are 5 bacterial strain in the V2-V5 variable region and 3 bacterial strain in the V6-V8 variable region of 16S rRNA gene segment. There are 4 desulfuration bacterium to belongα—Proteobacteria, and can be placed in Rhodoplanes, Bradyrhizobiaceae, Rhizobiales, and another 4 belong toβ-proteobacteria. The results indicated there are large of microorganism classification in the the desulfuration bacterium, and they are exertion biology function to transfer SO2 with their synergy. The discovery about the desulfuration bacterium have an important value for devolpment way of microorganism desulfuration from fuel gas.The immobilization desulfuration bacterium ball with 251.3%of comparatively activity, high mechanical strength and acid resistance and heat stability can be made by the technology for complexed immobilized bacterium with adsorption by activated carbon, embedded by 5%of sodium alginate, and immobilized drop in calcium chloride, then crosslinked 40 min in 0.06mol/L of hexamethylene diamine liquid. The immobilization desulfuration bacterium ball can be satisfied long period running in fixed bed, and the immobilized desulfuration bacterium degrades SO32- in aqueous solution satisfied also M-M equation as free desulfuration bacterium, and the parameter of kinetics equation: rmax=3311mg/L.h, Km=6613mg/L. The Thiele modulus (Φ) is 0.628 at 2.5mm the diameter of the mmobilized bacterium ball, and the degradation process of immobilized bacterium to SO32- is mainly controlled by reaction. The diffusion of substrate in the ball have some influenced at the diameter of the mmobilized desulfuration bacterium ball is over 3mm. The degradation rate of the mmobilized bacterium at the 25mm of ball diameter, pH=3, T=30℃is same with free desulfuration bacterium, and the degradation kinetics for SO32- is first order reaction under 30℃of the system temperature, where the reaction rate constant is k= 1.62xl09exp(-6077.7/T), the activation energy isEa=50.53 (kJ/mol). That showed the. desulfuration mechanism to SO32-is the same with that of free desulfuration bacterium.The fixed bed biochemical reactor with 42mm of tower diameter,100mm of high filled 25mm immobilized desulfuration bacterium ball, have a lesser startup time and a high removing SO2 efficiency over 96%and biochemical removal quantity over 6kg[SO2]/(m3.h) for low concentration SO2 gas at pH=3-4 of cycled spraying liquid,20℃of operation,8s of gas residence time. The result showed that biochemical removal quantity in fixed bed biochemical reactor is higher than that of free desulfuration bacterium. When the activity of immobilized desulfuration bacterium in fixed bed reactor is inactivation, it is effective to spray cycled liuquid and aeration air into the fixed bed reaction. When the tester plants have been used to remove SO2 of 2000mg/m3 from fuel oil tail gas and fuel coal tail gas in a catering industry, it showed that the reactor run stable, there are any SO2 to be detected at outlet (detection limit of 1mg/m3), and the removing efficiency is near to 100%. So the fixed bed biochemical reactor is possible for removal SO2 from fuel gas.The kinetics equation about cell growth of immobilized desulfuration bacterium in this bio-reactor is and that of substrate consumed is The mechanism of removing SO2 by fixed bed bio-reactor is that the SO2 in the gas is that the SO2 is diffluence in liquid, then diffusing into immobilized ball for desulfuration bacterium using. Which the process belong to heterogeneous microorganism reaction include mass tranfer of SO2 and other substance in gas-liquid-solid. It is discover that the SO2 is a alone restricted substance by immobilized desulfuration bacterium removal SO2 from low concentration SO2 gas, and the mass transfer of SO2 in immobilized ball is one of main factor for removing SO2. And the internal diffusion of SO2 in the ball is related with the face concentration of substrate and semidiameter of ball, and the concentration distribution in the ball can be described with The kinetics model for fixed bed bio-reaction removal SO2 can be showed as which include the character of immobilized desulfuration bacterium, internal diffusion factor, dimension of fixed bed bio-reactor, and operation condition and so on. The model prediction results have a good coherence with experiment data. So the kinetics model can provide a theory guide for optimizing of operation condition, enlarge design of the bio-reactor, and forecast of the desulfur ability.