where Rbefore, Rafter and Rnew are the resistances (m1) before and
after cleaning of the membrane and of the new membrane,
respectively.
The results (data not shown) indicate that the cleaning efficiency reached 24% at an N2 flow rate of 20 L/h, which was inferior
to the efficiency obtained at a flow rate of 40 L/h (36%). Increasing
the gas flow rate caused a more intense shock effect on the gel
layer formed at membrane surface, which resulted in a higher
cleaning efficiency. However, the increase in the cleaning efficiency
decreased (36–46%) when the flow rate was increased from 40 to
80 L/h. This behavior was primarily caused by the adherence of
the residual foulant in the membrane pores, which was difficult
to flush. In addition, the cleaning efficiency increased rapidly within the first 20 min and gradually stabilized at a certain value in the
following 40 min. Hence, considering the energy conservation, the
optimum N2 flushing mode was determined to be a 40 L/h N2 flow
rate with a 20-min cleaning phase.