Zhang S, Splendiani A, dos Santos L M, Livingston A G
Department of Chemical Engineering and Chemical Technology, Imperial College of Science, Technology and Medicine, University of London, London SW7 2BY, UK.
Biotechnol Bioeng. 1998 Jul 5;59(1):80-9.
A novel technique has been used to determine the effective diffusion coefficients for 1,1,2-trichloroethane (TCE), a nonreacting tracer, in biofilms growing on the external surface of a silicone rubber membrane tube during degradation of 1,2-dichloroethane (DCE) by Xanthobacter autotrophicus GJ10 and monochlorobenzene (MCB) by Pseudomonas JS150. Experiments were carried out in a single tube extractive membrane bioreactor (STEMB), whose configuration makes it possible to measure the transmembrane flux of substrates. A video imaging technique (VIT) was employed for in situ biofilm thickness measurement and recording. Diffusion coefficients of TCE in the biofilms and TCE mass transfer coefficients in the liquid films adjacent to the biofilms were determined simultaneously using a resistances-in-series diffusion model. It was found that the flux and overall mass transfer coefficient of TCE decrease with increasing biofilm thickness, showing the importance of biofilm diffusion on the mass transfer process. Similar fluxes were observed for the nonreacting tracer (TCE) and the reactive substrates (MCB or DCE), suggesting that membrane-attached biofilm systems can be rate controlled primarily by substrate diffusion. The TCE diffusion coefficient in the JS150 biofilm appeared to be dependent on biofilm thickness, decreasing markedly for biofilm thicknesses of >1 mm. The values of the TCE diffusion coefficients in the JS150 biofilms <1-mm thick are approximately twice those in water and fall to around 30% of the water value for biofilms >1-mm thick. The TCE diffusion coefficients in the GJ10 biofilms were apparently constant at about the water value. The change in the diffusion coefficient for the JS150 biofilms is attributed to the influence of eddy diffusion and convective flow on transport in the thinner (<1-mm thick) biofilms.
一种新技术被用于测定1,1,2 - 三氯乙烷（TCE，一种非反应性示踪剂）在自养黄色杆菌GJ10降解1,2 - 二氯乙烷（DCE）以及假单胞菌JS150降解一氯苯（MCB）过程中，在硅橡胶膜管外表面生长的生物膜中的有效扩散系数。实验在单管萃取膜生物反应器（STEMB）中进行，其结构使得测量底物的跨膜通量成为可能。采用视频成像技术（VIT）原位测量和记录生物膜厚度。使用串联阻力扩散模型同时测定了TCE在生物膜中的扩散系数以及与生物膜相邻的液膜中TCE的传质系数。结果发现，TCE的通量和总传质系数随着生物膜厚度的增加而降低，这表明生物膜扩散在传质过程中具有重要作用。对于非反应性示踪剂（TCE）和反应性底物（MCB或DCE）观察到了相似的通量，这表明膜附着生物膜系统的速率主要受底物扩散控制。JS150生物膜中TCE的扩散系数似乎取决于生物膜厚度，对于厚度大于1 mm的生物膜，扩散系数显著降低。厚度小于1 mm的JS150生物膜中TCE扩散系数的值约为水中的两倍，而对于厚度大于1 mm的生物膜，该值降至水值的约30%。GJ10生物膜中TCE的扩散系数显然恒定在约水值。JS150生物膜扩散系数的变化归因于涡流扩散和对流对较薄（厚度小于1 mm）生物膜中传输的影响。
