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Study on effect of membrane fiber length on critical flux in a novel membrane bioreactor

摘要：为了优化膜-生物反应器中的膜组件长度,考察了4组不同长度膜组件(膜丝长度为0.2、0.4、0.6、0.7m)在不同曝气量下的临界通量区.试验结果发现,曝气强度相同时,膜丝长度为0.4m膜组件的临界通量区高于膜丝长度为0.2m、0.6m和0.7m的膜组件,说明膜丝长度存在最优值;膜组件中膜丝长度相同时,曝气强度越大临界通量区越高.膜丝(膜组件)长度对临界通量产生影响主要体现在2方面:一是膜丝长度的变化会改变膜丝上局部通量的非均匀分布状况;二是曝气气泡对不同长度膜丝的冲刷作用不同.应用局部通量分布方程模拟了清洁膜丝上局部通量的分布状况;结果表明,膜丝长度越长,沿膜丝长度方向的局部通量分布越不均匀,则膜组件的临界通量越小.从曝气气泡对膜丝的冲刷作用看,相同曝气量下膜组件(即膜丝)长度越长,形成的气泡越大,在大气泡的作用下膜丝更易于摇摆和震动以达到减轻膜表面污染物沉积的效果,即可能达到的临界通量越大.因此,对于减轻膜污染而言,即得到最高的临界通量区,膜丝(膜组件)长度存在最优值.

Abstract：Critical flux plays an important role in the control of membrane fouling in membrane bioreactors.Experiments were conducted to determine the critical flux region of four membrane modules with different membrane fiber lengths,under different aeration intensity.The results show that:① the membrane module with a membrane length of 0.4 m had the highest critical flux region(compared to 0.2 m,0.6 m and 0.7 m)at the same aeration intensity;② critical flux improved as the aeration intensified in the same membrane module.The influence of membrane fiber length on critical flux mainly occurs through two mechanisms:the flux distribution along the membrane fiber and the fiber shaking effect due to aeration.According to the results simulated from a flux distribution function,the non-uniformity of flux along a membrane fiber increases with the membrane fiber length,leading to a lower critical flux.The longer the membrane module(fiber)is,the bigger the air bubbles are that are formed under the same aeration intensity,and also the easier for the membrane fiber to shake and vibrate which reduces the deposition of foulant onto the membrane surface,and therefore a higher critical flux is reached