细胞表面疏水性对两相分配体系净化正己烷废气的作用机制

The removal of volatile organic compounds (VOCs) (e.g. n-hexane) with high hydrophobicity has been a difficult issue in the field of waste gas treatment by biotechnology. Though the development of two-phase partitioning system employing silicone oil and water provides the possibility in the purification of this kind of waste gas, pollutant still suffers from the limitation of mass transfer from non-aqueous phase to microorganism, which usually results in the low elimination efficiency. This project aims to increase n-hexane removal efficiency in a two-phase partitioning system employing silicone oil and water by enhancing cell surface hydrophobicity (CSH) of Pseudomonas oleovorans DT4. CSH enhancing methods and its enhancing mechanism will be explored. Then the effect of CSH on the behavior of n-hexane mass transfer among different phases in the two-phase partitioning system will be investigated. The tendency of microorganism closing to silicone and subsequently the mass transfer mechanism of n-hexane among these phases will be analyzed. The property of the key enzyme and the degradation activity of P.oleovorans DT4 after CSH enhancement will be characterized, and the metabolism characteristics of n-hexane degradation in aqueous phase,non-aqueous phase and interface will be clarified. Then, the mass transfer and reaction dynamic model of n-hexane removal in two-phase partitioning system employing the microorganisms with varied CSH will be established. Furthermore, the mechanism of the CSH influencing rate-limiting step of n-hexane mass transfer and reaction processes will be revealed, thus laying sound foundation for the purification of waste gas containing highly hydrophobic VOCs by two-phase partitioning system.

以正己烷为代表的强疏水性VOCs的去除一直是废气生物净化领域的难题。虽然硅油-水两相分配体系的构建为该类废气的净化提供了可能，但由于污染物从非水相至微生物的传质仍然受到限制，两相分配体系对强疏水性VOCs的去除效果并不理想。 本申请拟通过强化Pseudomonas oleovorans DT4细胞表面疏水性（CSH）提高硅油-水两相分配体系净化正己烷废气的性能，探索CSH的强化方法与机理；研究CSH对相间传质行为的影响，解析不同CSH微生物对硅油的趋向性以及正己烷多相传质规律；表征CSH强化后P. oleovorans DT4关键酶性质与降解活性，阐明微生物在水相、非水相和界面的代谢特征；建立不同CSH下的两相分配体系净化正己烷废气的传质-反应动力学模型，解析CSH对正己烷传质-反应过程限速步骤转化的影响机制，为两相分配体系高效脱除废气中强疏水性VOCs的应用奠定基础。

以正己烷为代表的强疏水性VOCs的去除一直是废气生物净化领域的难题。本研究项目通过强化Pseudomonas mendocina NX-1的细胞表面疏水性（CSH），为正己烷的传质提供了新的途径，提高了硅油-水两相分配体系净化正己烷废气的性能。. 利用调节pH、淀粉及壳聚糖浓度强化P. mendocina NX-1的CSH，结合Box-Behnken设计和响应面分析，P. mendocina NX-1的CSH在优化条件下从15%升高到56%。与低CSH的NX-1细胞相比，高CSH的NX-1分泌的胞外多糖含量减小，胞外蛋白含量和Zeta电位增加，且红外光谱结果显示在细胞表面出现了新的脂质和蛋白质。利用Haldane模型拟合不同CSH的NX-1降解正己烷的数据，结果发现56% CSH的NX-1比降解速率为0.72 mg•(mg cell)-1•h-1，是15% CSH细胞比降解速率的2倍。. 进一步地，通过向两相分配体系（TPPB）中添加0.3%(w/v)壳聚糖构成含壳聚糖两相分配体系（KTPPB）以强化正己烷废气的净化性能。KTPPB系统和TPPB系统的最大去除负荷分别为21.39 g•m-3•h-1和13.25 g•m-3•h-1。通过激光共聚焦显微镜观察，发现KTPPB中的菌体会在硅油液滴附近聚集。CSH的提高使得更多微生物粘附在硅油/水界面，导致界面微生物可以直接从硅油表面吸收正己烷，增加了一条从气相到生物相的底物传质路径，从而大大加快正己烷的传质效率。. 结合“等价吸收容量”和动态法，建立传质模型并计算气相往液相中传递的最大底物分数βS*和最大体积传质速率Nmax，发现在不同进气流量下βS*值均能提高3倍以上。通过比较Nmax值和最大去除负荷ECmax值，发现基于10%硅油的两相体系在处理正己烷废气的过程中，底物传质过程仍然是限速步骤。基于质量守恒构建了具有普适性的两相传质-反应动力学模型，发现CSH强化后硅油表面的生物量是决定该模型拟合度高低的关键因素之一。