生物—化学法净化甲醛废气应用基础研究

【作者】 李晓梅；

【导师】 潘学军； 段希祥；

【作者基本信息】 昆明理工大学 ， 环境科学， 2014， 博士

【摘要】 生物法废气净化新技术研究是现阶段低浓度废气治理技术研究领域中广受关注的前沿热点之一。由于甲醛兼有水溶性和挥发性的特殊性,使得采用生物法对低浓度甲醛废气的处理方式与其它有机废气的处理方式具有不同的特征,如何实现对废气中甲醛的高效生化降解去除是近年来研究获得生物法净化甲醛废气实用工程技术所面临的一个难题。本论文研究针对生物膜填料塔降解净化甲醛废气技术应用中,存在的气态甲醛溶解并累积于循环液而导致废气中甲醛不能被高效生化降解去除的技术难题,开展了采用添加化学促进剂强化生物膜填料塔降解净化甲醛废气性能的应用基础研究,重点对高效化学促进剂的选择及其强化生物膜填料塔降解净化甲醛废气性能的可行性、适用高效化学促进剂亚硫酸钠对微生物菌种及优势种群的影响、提高生物膜填料塔降解净化甲醛废气性能的最佳操作条件、甲醛降解过程机理与降解途径以及相关基础动力学等进行了系统的应用基础研究,以期通过探索研究“化学促进-生物降解”集成优化于生物膜填料塔对甲醛废气降解净化效果的突跃增强作用,为解决生物法净化甲醛废气技术应用中的技术难题提供一个有效途径。首先,本研究通过实验证实,当生物膜填料塔在气体流量为0.2m3/h、循环液流量为5L/h、进口气体甲醛浓度范围50～150mg/m3的条件下操作时,溶解在循环液中的甲醛累积浓度可达8.45～33.00mg/L。对应进行的去除累积甲醛的化学促进剂选择实验结果表明,当按与液相甲醛化学反应摩尔比为1：1添加化学试剂时,在实验选用的亚硫酸钠、亚硫酸氢钠、氯化铵等三种试剂中,以亚硫酸钠对液相甲醛的去除率最高,达到了68.69%。进一步实验考察亚硫酸钠添加浓度变化对生物膜填料塔系统中液相甲醛去除效果的结果表明,当亚硫酸钠浓度由0.05M增加到0.15M时,液相甲醛去除率随之升高,最高可达到99.98%。综合考虑工业木材生产过程中甲醛废气的排放浓度、本研究的目标以及生物膜填料塔系统操作运行的经济性等方面的因素,本研究选择亚硫酸钠作为最适用化学促进剂并以0.05M为适宜添加浓度开展后续相关研究。采用亚硫酸钠强化生物膜填料塔净化甲醛废气性能的可行性研究结果表明,在相同的实验条件下,采用浓度为0.05M亚硫酸钠循环液的生物膜填料塔(2号塔)的循环液中甲醛溶解累积的最大浓度值,比不添加亚硫酸钠的生物膜填料塔(1号塔)的减小了99.2%。随着循环喷淋液流量及进口气体甲醛浓度的增加,虽然两个生物净化塔的甲醛降解效率均可维持在96.6～100%的水平上,但2号塔的甲醛生化降解量随之增加(分别增加约0.02及1.5倍),而对应的不添加亚硫酸钠的1号塔的甲醛生化降解量则大幅度持续减小(分别减小约1.8及2.2倍),也即甲醛溶解累积量快速增加。这一结果证实了亚硫酸钠对溶解累积在循环液中的甲醛具有很强的去除作用,同时也验证了采用亚硫酸钠作为促进剂强化生物膜填料塔对甲醛废气的降解净化性能是可行的。通过应用PCR-DGGE、PCR扩增16Sr RNA、基因组总DNA提取及构建系统进化树等分子生物学研究方法,研究添加亚硫酸钠对降解甲醛微生物优势种群影响的结果表明,采用亚硫酸钠能够促进甲醛降解菌群体的快速生长,并通过延长甲醛降解菌的生长稳定期大幅度提高优势种群降解甲醛的能力,同时也使甲醛降解微生物系统中的优势种群出现了明显变化。其中由于添加亚硫酸钠而新检出的一类甲醛降解菌(甲基营养菌)-副球菌,能够在亚硫酸钠的刺激下强势生长,使其转变成为优势种群,并在甲醛的生化降解过程中发挥重要作用。为了进一步确认亚硫酸钠的强化作用效果,采用在添加亚硫酸钠的作用环境中驯化得到的微生物优势种群液挂膜的生物膜填料塔(3号塔),与仅采用以浓度为0.05M亚硫酸钠循环液的生物膜填料塔(2号塔)进行的对比实验结果表明,在相同条件下随着进口气体甲醛浓度及气体流量增加,3号塔的甲醛生化降解量的最大值分别达到61.1及112.4mg/L.h,其值远大于对应的2号塔对甲醛最大生化降解量分别仅为5.3及3.08mg/L.h的结果。这充分体现出了“化学促进-生物降解”集成优化于3号塔对甲醛降解效果的突跃增强作用。通过正交试验研究确定了3号塔的最佳操作条件是：循环液流量为5L/h,进口气体甲醛浓度为80mg/m3,气体流量为0.4m3/h。对3号塔中优势种群降解废气中甲醛的气、液相主要产物的分析结果表明,气相甲醛的最终生化降解产物主要为CO2,液相中的亚硫酸钠可与溶解的甲醛反应生成羟甲基磺酸钠,其可作为微生物生长的碳源被微生物降解及利用。通过对添加亚硫酸钠的生物膜填料塔降解甲醛废气的生化反应机理和降解途径的研究得知,添加亚硫酸钠的生物膜填料塔的生物膜中甲醛的生化反应速率小于它在液膜中的扩散速率,为一级慢速生化降解反应,亚硫酸钠显著强化了生物膜降解甲醛的生化反应过程,其降解净化甲醛废气的表观生化反应速率Ra值比不添加亚硫酸钠的生物膜填料塔的Ra值提高了363.3%,甲醛生化反应一级反应速率常k1*提高了216.8%。对应的微生物学分析表明,添加亚硫酸钠强化了生物膜填料塔对废气中甲醛的生化去除效果,其实质是亚硫酸钠刺激了降解甲醛优势种群中的甲基营养菌假单胞菌和副球菌的快速生长,从而使构成生物膜优势种群主体的甲基营养菌假单胞菌和副球菌能够共同通过异化和同化途径将其捕获的甲醛代谢为CO2和细胞能量,使甲醛得以生化降解完全。对添加亚硫酸钠的液相微生物降解甲醛动力学和生物膜填料塔系统净化甲醛废气的相关动力学研究结果表明,对于添加亚硫酸钠的生物膜填料塔系统,其液相甲醛生化降解动力学过程符合Monod模式,其模型计算值与实验值之间有很好的相关性,相关系数R=0.9852。由于添加亚硫酸钠的作用,使得微生物降解液相甲醛一级生化反应的甲醛浓度提高了11%,反应速率常数提高了7%,最大比降解速率提高了15.9%。这一结果证实了添加的亚硫酸钠对微生物在液相对甲醛的降解过程发挥了明显的促进作用。对采用亚硫酸钠强化的生化降解净化甲醛废气过程的适用动力学模型的对比验证结果表明,采用“吸收-生物膜”理论动力学模型的计算值与实验值的相关性(相关系数0.9297～0.9441)明显优于采用“吸附-生物膜”理论动力学模型的计算值与实验值的相关性(相关系数0.5982～0.7650)。这表明“吸收-生物膜”理论动力学模型适合于描述本研究采用亚硫酸钠强化的生物膜填料塔降解净化甲醛废气的动力学过程。本论文研究通过采用亚硫酸钠促进剂将“化学促进-生物降解”集成优化于生物膜填料塔净化系统中,使生物膜填料塔对甲醛废气的降解净化性能实现了突跃增强,初步形成了一项具有“化学促进-生物降解”特性的高效降解净化甲醛废气新技术。该项新技术在有效解决气态甲醛溶解并累积于循环液而导致废气中甲醛不能被高效生化降解的技术难题,以及有效提升生物膜填料塔对甲醛废气的降解净化性能方面具有重要的突破意义。本研究成果将在工业低浓度甲醛废气净化污染控制方面具有广阔的应用前景。更多还原

【Abstract】 Developing biology-based technologies for low-concentration waste gas purufication has been a hot research topic in the field of waste gas purification. Due to the fact that formaldehyde is water-soluble and vaporable, it is challenging for using existing biology-based technologies to efficiently purify low concentration formaldehyde waste gas.In the thesis, studies were conducted to overcome the challenge in purifying formaldehyde waste gas with biotrickling filter, which is, due to water solubility of formaldehyde gas, accumulation of formaldehyde in circulating liquid leads to limited formaldehyde purification efficiency. The studies were focused on investigating:feasibility of adding chemicals in a biotrickling filter to enhance formaldehyde purification; effect of sodium sulfite on the microorganisms that degrade formaldehyde; optimal operation parameters in the proposed biotrickling filter; mechanisms and kinetics of formaldehyde degradation in the biotrickling filter. The aim was to develop a new type of biotrickling filter which employs "chemical-reaction enhanced degradation" to purify low concentration formaldehyde waste gas with high efficiency.Experiments showed that when inlet gas flow rate was0.2m3/h, circulating liquid flow rate was5L/h, and inlet formaldehyde gas concentration was50-150mg/m3, concentrations of formaldehyde accumulated in the circulating liquid were found up to8.45～33.00mg/L. Under the condition, sodium sulfite, sodium bisulfite, and ammonium chloride were added, respectively, with Molar ratio of1:1between the chemical concentration and formaldehyde concentration in the circulating liquid. It was shown that adding sodium sulfite led to highest removal efficiency of formaldehyde in the liquid, which was up to68.69%. Experiments also showed that when the concentration of sodium sulfite was increased from0.05M to0.15M, the removal efficiency of formaldehyde in the liquid was up to99.98%. Based on the consideration of concentration level of formaldehyde waste gas from wood-processing industry and economical operation of a biotrickling filter, sodium sulfite of0.05M was used in the studies.Experiments comparing performances of two biotrickling filters (filter1without sodium sulfite and filter2with0.05M sodium sulfite) showed that the maximum concentration of formaldehyde in circulating liquid in filter2was99.2%lower than that in filter1. When the flow rate of circulating liquid and inlet formaldehyde gas concentration were increased, though formaldehyde degradation efficiencies of the two filters were similar in the range of96.6～100%, biochemical degradation of formaldehyde in filter2was increased by factors of0.02and1.5, respectively. Whereas the biochemical degradation of filter1was decreased by factors of1.8and2.2, respectively, which indicated that the amount of formaldehyde accumulated in circulating liquid was increased in filter1. The results showed that adding sodium sulfite led to remarkable removal of formaldehyde in the liquid and it is feasible to use sodium sulfite in a biotrickling filter to enhance purification of formaldehyde waste gas.The affect of sodium sulfite on the dominant bacteria which degraded formaldehyde in the biotrickling filter was studied using PCR-DGGE, PCR amplified16S r RNA, and genomic DNA techniques. The results showed that sodium sulfite accelerated the growth of the bacteria and extended the stable period of the bacteria, and therefore enhanced the degradation of formaldehyde. A new type of bacteria which can degrade formaldehyde, Methylotrophic bacteria-Paracoccus bacteria, was found when sodium sulfite was added. The bacteria grew rapidly under the stimulation of sodium sulfite and became the dominant bacteria, which played an important role in formaldehyde degradation.Comparison experiments were conducted to further examine formaldehyde degradation enhancement caused by sodium sulfite. Sodium-sulfite adapted dominant bacteria were used to hang film and the film was used in a biotrickling filter (filter3). The performance of filter3was compared with that of filter2. Sodium sulfite was added in both filters. The difference between the filters was that filter2did not use sodium-sulfite adapted bacteria for hanging film. With the increase of inlet formaldehyde gas concentration and inlet gas flow rate, the maximum amount of formaldehyde biochemical degradation in filter3were61.1and112.4mg/L-h, which were much larger than those of filter2(5.3and3.08mg/L-h). The results demonstrated significant improvement of formaldehyde degradation with the "chemical enhanced degradation". The optimal operation parameters of filter3were determined based on orthogonal tests:circulating liquid flow rate of5L/h, inlet formaldehyde gas concentration of80mg/m3, and gas flow rate of0.4m3/h. It was found that the product of formaldehyde gas degradation was CO2, and the reaction of sodium sulfite with formaldehyde in the liquid produced CH2(OH)SO3Na,which can be degraded by microorganisms and can be used as carbon source for microorganisms.The mechanism of the biochemical reactions in the formaldehyde degradation and the pathways of degradation were investigated. The results showed that in the biotrickling filter where sodium sulfite was added, the biochemical reaction rate in the biofilm was smaller than the diffusivity. The reaction was first-class slow biochemical degradation reaction. As a result, the biochemical reaction was significantly enhanced. Apparent biochemical reaction rate Ra and first-class reaction constant k1of the biochemical reaction were increased by363.3%and216.8%, respectively, in the biotrickling filter with sodium sulfite, compared to a regular biotrickling filter. It was found that sodium sulfite stimulated the growth of Methylotrophic bacteria-Pseudomonas bacteria, and Paracoccus bacteria, the dominant bacteria which degraded formaldehyde through assimilation and dissimilation. Because the products were CO2and cell energy, it was a complete degradation.The study of the kinetics of formaldehyde degradation in the biotrickling filter where sodium sulfite was added, showed that the kinetics of formaldehyde degradation in the liquid could be described with the Monod model. The model predictions had good correlation with measurements. The correlation coefficient R is0.9852. Due to the effect of sodium sulfite, the formaldehyde concentration was increased by11%, the reaction rate constant was increased by7%, and the maximum degradation rate was increased by15.9%. The results demonstrated that sodium sulfite significantly enhanced formaldehyde degradation in the liquid. The results also showed that the quantities calculated using the "absorption-biofilm" kinetics model had better correlation with experiments (correlation coefficients:0.9297～0.9441) than those calculated using the "adsorption-biofilm" kinetics model (correlation coefficients:0.5982～0.7650). This indicated that the kinetics of the sodium-sulfite enhanced formaldehyde degradation can be described with the "absorption-biofilm" kinetics model.In the thesis, a biochemical method which utilized sodium sulfite to achieve chemical-enhanced degradation in a biotrickling filter, was proposed and studied. The studies showed that with this new technology, formaldehyde waste gas purification was improved remarkably. The technology overcomes the challenge that the efficiency of formaldehyde waste gas purification in a regular biotrickling filter is limited due to that formaldehyde gas is water soluble and is accumulated in the circulating liquid. The study results will have significant impact in the field of formaldehyde waste gas purification and the technology will have wide applications in treatment of low concentration formaldehyde waste gas from industry.更多还原