The use of intermittent gas bubbling to control membrane fouling in concentrating TCM extract by membrane distillation

This study investigates the growth of fouling resistance and fouling limitation through gas bubbling in concentrating the extract of traditional Chinese medicine (TCM) by direct contact membrane distillation (DCMD). Expressions describing the growth rate of fouling resistance and flux decline in concentrating TCM extract by DCMD were deduced. The predicted flux decline by these expressions accords with obtained experimental results, implying that the growth of fouling layer follows the proposed mechanism. To limit membrane fouling or flux decline during concentrating process, intermittent gas bubbling was introduced to the feed side of membrane module. It was confirmed by experimental results that membrane fouling was effectively controlled in the way of removing deposited foulants from membrane surface by created two phase flow. It was also found that the cleaning efficiency of gas bubbling could be improved with the increase of gas flow rate, gas bubbling duration, and the decrease of membrane distillation (MD) duration. These factors combined to affect the cleaning efficiency, and the process productivity may be maximized by the optimization of these gas bubbling conditions.

Research highlights
► Expressions describing the growth rate of fouling resistance in DCMD were deduced.
► The growth of fouling resistance can be well described by proposed fouling mechanism.
► Membrane fouling could be effectively controlled by intermittent gas–liquid two phase flow.
► Gas flow rate, bubbling and MD duration combine to affect cleaning efficiency.