【作者】 陈浚；

【导师】 陈建孟；

【作者基本信息】 浙江工业大学 ， 生物化工， 2009， 博士

【摘要】 氮氧化物（NO_x）是导致酸雨、光化学烟雾等一系列严重大气污染的主要污染物之一,随着NO_x污染问题的日趋严重和人们对环境质量要求的不断提高,有关废气脱氮技术的研究已迫在眉睫,而这方面的实用治理技术与基础理论研究（如生物法脱氮）却少有突破。它的发展是继废气脱硫之后所面临的又一亟待解决的重大课题。研究采用一种新型的生物过滤器—生物转鼓（Rotating Drum Biofilter,RDB）净化一氧化氮（NO）废气,围绕转动生物膜及络合协同强化NO的去除过程,以传质理论和生化反应动力学为基础,探讨各反应组分在气、液、生物膜三相中的独特传质-反应规律;阐明反硝化（络合协同）去除NO过程中氮素传递、转化等作用机理,建立NO净化过程的物料平衡和动力学模型;运用微生物学和分子生物学技术研究RDB中微生物种群结构和优势菌种。主要内容和结果如下:（1）考察了RDB净化NO废气的工艺特征。在250℃-30℃、pH 6.5-7.5、转鼓转速0.5 r/min、空床停留时间（Empty Bed Residence Time,EBRT）86.4 s,进口NO浓度120-584 mg/m³的条件下,RDB能有效净化NO废气,去除率达60.0%-85.2%。转速影响RDB膜表面更新和液膜厚度,在转速0.5 r/min时NO去除率达最大。在进气负荷小于20 g/m³·h时,去除负荷随进气负荷增加而线性增加,且去除率在75%以上;随着进气负荷进一步增大,去除负荷上升趋缓并接近极限容量（约27.5 g/m³·h）。葡萄糖、醋酸钠、甲醇渐次为RDB反硝化NO的合适碳源,由于NO的传质限制,碳源的过量投加并不能有效改善其去除效率。pH=8的弱碱环境有利于系统维持较高的去除效率,在500 mg/m³的进气浓度下,去除率和负荷分别达75.0%和16.0 g/m³·h。进气中适量的氧气可以增加NO的氧化度,从而提高NO的气液传质速度和生物净化效率,但过量氧气会破坏RDB的厌氧环境,抑制反硝化菌活性,研究表明此临界值等于6%。温度变化对RBD去除较低浓度NO的影响不大,而随着浓度上升,温度变化的影响加剧,实验表明30℃为最佳反应温度。（2）分析了NO在RDB内的转化途径、氮素价态变化和物料平衡。在稳态运行下（130d-40d,NO进气浓度273-378 mg/m³）,出气中N₂和N₂O含量分别达92-131 mg/m³和9.2 mg/m³,平均转化率为72.0%和0.5%,而剩余的5%和12%-15%的NO则分别以氧化态形式积累于液相和被微生物同化利用。根据细菌生长总反应方程,对RDB内反硝化过程的氮素计量学进行了推导,发现lmolNO中的氮素可以转化为0.18mol的生物质氮和0.82mol的氮气,这与实验结果基本一致。对RDB内氮素进行了11日物料平衡核算,表明系统内氮素基本守恒,出口氮素质量占进口氮素质量的比例在93.5%-99.6%之间波动。（3）开展了络合协同RDB增强NO去除的研究。实验发现,在营养液中添加Fe^Ⅱ（EDTA）络合物可显著改善难水溶性NO的气液传质速率,从而提高其去除效率。在转速0.5r/min、EBRT 57.7s、300℃、pH 7.0-8.0的条件下,Fe^Ⅱ（EDTA）的逐量增加（0-500 mg/L）可使RDB对380 mg/m³的NO去除率从61.1%升至99.6%。在此体系下,乙醇优于葡萄糖作为Fe^Ⅱ（EDTA）NO反硝化的电子供体,当TOC浓度超过1000 mg/L后,NO的去除率达到稳定。实验最佳pH在8.0左右,最适温度随Fe^Ⅱ（EDTA）添加浓度的增加而上升。（4）研究了NO在RDB内的传质-反应过程。通过分析NO在气相、液相和生物相的质量平衡,建立了RDB净化NO废气的传质-反应数学模型。该模型可近似描述低浓度（<600 mg/m³）NO废气在RDB中的浓度分布和去除效率。修正后的方程如下:模型预测的结果与实验值基本相符,验证了RDB生物反应器与传统生物反应器相比具有生物量分布均匀、填料不易堵塞等优点。（5）探析了RDB内的微生物种群结构。运用PCR-DGGE技术对RDB内的生物多样性进行了解析,共发现16种优势种属,且沿填料径向的种群结构差异性不大;通过样品的聚类分析和多样性指数计算,发现RDB内微生物群落多样性随Fe^Ⅱ（EDTA）络合剂的加入呈先增加后下降的趋势,但其在整体演变过程中变化不显著;对DG-DGGE图谱中8个主要条带进行回收、扩增、克隆和测序,结果表明,RDB中微生物群落主要由Clostridium sp.、β-proteobacterium、γ-proteobacterium和Cytopahga-Flexibacte-ria-Bacteroides（CFB） groups Bacteroides组成。反硝化功能与γ-proteobacterium和β-proteobacterium所代表的种属相关。（6）分离筛选了1株RDB的好氧反硝化菌DN3,并进行了反硝化性能测试。研究表明,该菌株能较好地反硝化降解硝酸盐,并只产生少量亚硝酸盐。在碳源不足的条件下（C/N=3）,DN3对NO₃^--N去除率为72.9%;通过16SrDNA序列分析及同源性比对,DN3与Pseudomonas putida.的相似性为100%。其反硝化最适温度和pH值分别为30℃和7.0,最适宜C/N在5.5-6.0,在该区间内能进行完全的反硝化。更多还原

【Abstract】 Nitrogen oxides （NO_x） are the hazardous compounds to the environment, which play a key part in the photochemically induced catalytic production of ozone and which also result in nitric acid deposition. The pollution of NO_x has been gaining enormous attention throughout the world, with the increasing emission amount of NO_x to the atmosphere and the increasing demands for the control of environmental quality. Many countries have established stringent regulations on NO_x emissions. Current technologies for NO_x removal from the flue gas have been associated with many problems, such as high cost, produced secondary pollutant and/or low removal efficiency. On the other hand, the difficulty in the removal of NO from flue gas has increased due to the large emission amount of flue gas and the low solubility of NO, the main component of NO_x in the flue gas. Therefore, the research on NO removal from the flue gas has been becoming a hot issue of air pollution control presently.An innovative rotating drum biofilter （RDB） has been developed and applied as an effective technique for NO removal in the investigation. The aims of the work are to demonstrate its feasibility and optimize the treatment of NO in RDB utility. The effect of operating parameters such as inlet pollutant loading, temperature and pH, et al., on bioreactor performance has been studied in the RDB packed with an open-pore reticulated polyurethane sponge. In the process of nitric oxide （NO） denitrifying removal by the RDB, a dynamic model has been developed and further validated. In order to enhance the understanding of the relationship between the composition of bacterial population and the performance of the RDB, the total microbial population and the population of the denitrifying bacteria in the RDB are characterized by targeting the 16S rRNA and DGGE. The aims of this work are to provide both a new method and some fundamental data for NO removal from the flue gas. The main experimental results are asfollows:1) The experimental results indicated that, under the conditions of temperature of 25℃-30℃, pH at 6.5 to 7.5, rotating speed of 0.5 r/min, empty bed residence time （EBRT） of 86.4 s, nutrient solution amount of 5 L and fresh nutrient solution of 0.2 L/d, it took about 30 days for the biofilm to become mature. In the five months’ stable operation, while the inlet NO concentration was 120-584mg/m³, the removal efficiency （RE） and elimination capacity （EC） were maintained at 60%-85.2% and 5-18g/m³·h, and the average were 68.7% and 11.6 g/m³·h, respectively. Drum rotating speed influenced the surface renewal and the liquid film thickness. NO RE reached the maximum when the rotating speed was 0.5r/min. The different carbon source on RDB performance was investigated and glucose was the best carbon source for NO RE. Excessive carbon source could not improve RE, but the expense would rise. EBRT was a key factor for influencing the denitrification process. Moreover, the RE increased as the O₂ concentration went up. At a lower range of NO concentrations （<100 mg/m³）, the temperature had no visible effects on the removal efficiency, whereas if NO concentrations got higher than 150mg/m³, a non-negligible enhancement of NO removal was found when the temperature was gradually rising from 25℃to 30℃. Furthermore, the results approved that the RDB had more advantages over traditional bioreactors in terms of low mass transfer resistance, high effective utility of packing materials, high even distribution of biomass, and no biomass clogging of packing materials.2) The transfer paths of NO in the RDB included chemical oxidization and biotransformation. The investigation focused on the changes of nitrogen valence state and analyzed the nitrogen balance of RDB. The results showed that between the stable operational periods from 130d-140d, the outlet concentration of intermediate （N₂O） was 9.2mg/m³, the average conversion from NO was 0.5%. The outlet concentration of final product （N₂） was between 92-131 mg/m³ and the average conversion was 72%. About 5% of inlet NO was accumulated in the liquid, and 12%-15% of NO was assimilated as nitrogen source by bacterium. Based on the above experimental data, the investigation analyzed the N balance of continues 11d operation of RDB. The results showed that the whole N mass balanced basically, and the ratio of N mass between outlet and inlet was 93.5%-99.6%.3) Due to the low solubility of nitric oxide （NO） in the liquid phase, improving gas-liquid mass transfer rate of NO was the key step in the whole process of NO denitrifying removal in the RDB. Therefore, the investigation on the addition of Fe^Ⅱ（EDTA） into the nutrient solution in the RDB was carried out. With the combination of NO and EDTA, NO dissolved in the liquid quickly. Under the experimental conditions of rotational speed at 0.5r/min, EBRT of 57.7s, temperature at 30℃、pH 7-8, with the increasing of the concentration of Fe^Ⅱ（EDTA） from 0 mg/L to 500mg/L, the average NO RE increased from 61.11% to 94.67%. The effects of other experimental conditions such as carbon source, temperature and pH were investigated. As a result, ethanol was better than glucose as the external carbon source on NO removal. As TOC was higher than 1000mg/L, NO RE reached stable. The optimal operating pH was 8, while the optimal temperature was rising with the increase of the concentration of Fe^Ⅱ（EDTA）.4) To illustrate the process of NO denitrifying removal by the RDB, a dynamic model has been developed and further validated. The model analyzed the mass transfer reaction process of NO in the RDB, focusing on the concentration distribution of NO in the gas, liquid, and biofilm phases, which was obtained by the mass component profile of NO at the gas-liquid interface combined with a Monod kinetic equation. The NO distribution equation on the biofilm carrier was thereby obtained, as well as a dynamic model for NO elimination in the test system. Additionally, operating parameters such as inlet NO concentrations and empty-bed residence time （EBRT） were evaluated through a sensitivity analysis for theoretically investigating their respective effects on NO removal efficiency. The model was therefore modified in consideration of the chemical absorption of NO by nutrition liquid in the bottom of RDB. The results demonstrated that the simulated data agreed well with the experimental data. The model made it possible to simultaneously obtain a relatively high NO removal efficiency in RDBs and to minimize the operating cost.5) A Denaturing Gradient Gel Electrophoresis of polymerase chain reaction-amplified genes coding for 16S rRNA was used to analyze and determine the changes in bacterial communities in the RDB. The results showed that there was a slight change in the microbial diversity after the addition of Cu^Ⅱ（EDTA） to the nutrient solution, which led to an increase in NO removal efficiency. Eight major bands of 16S rRNA gene fragments obtained from the DGGE gels of biofilm samples were further purified, reamplified, cloned and sequenced. The phylogenetic analysis identified sixteen types of microorganisms in the RDB. The sequences of these fragments were compared with those listed in the database of the GeneBank （National Center for Biotechnology Information）. The gene analysis of 16S rRNA showed that the major populations were Clostridium sp.,β-proteobacterium,γ-proteobacterium and Cytophaga-Flexibacteria-Bacteroides （CFB） groups. In addition, it was concluded that denitrification was caused by the organism with DNA represented by bands labelled G-5, G-6 and G-8. G-5 was related to aγ-proteobacterium, while those labelled G-6 and G-8 were related to aβ-proteobacterium.6) A bacterial strain DN3 screened from the RDB was found capable of aerobic denitrification and the denitrifying capability of strain was studied in batch culture under aerobic condition. When the concentration of carbon source was not abundant（C/N=3）, the nitrite accumulation and the removal rate of nitrate by strain DN3 were 41.17% and 72.91%. Phylogenetic analysis based on partial 16S rDNA and performed by MEGA showed that DN3 had 100% sequence similarity with Pseudomonas putida. The results indicated that the suitable temperature and pH value for aerobic denitrification were 30℃and 7.0, respectively. The denitrification performance of strain DN3 was almost not affected by the presence of oxygen and the strain DN3 had a high tolerance of dissolved oxygen concentration. The optimal C/N ratio was 5.5-6.0 and nearly complete denitrificaion could be obtained.更多还原