| Nitrogen oxides (NOx) 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 NOx has been gaining enormous attention throughout the world, with the increasing emission amount of NOx to the atmosphere and the increasing demands for the control of environmental quality. Many countries have established stringent regulations on NOx emissions. Current technologies for NOx 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 NOx 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 FeⅡ(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 FeⅡ(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 FeⅡ(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 CuⅡ(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.
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