3. Results and discussion
3.1. Effect of TMP on biofouling
The time courses of normalized permeate flux, J/J0, on the biofouling experiment at different TMPs are shown in Fig. 3, inwhich J0 is the initial permeate flux. The value of J/J0 decreased with time at all experimental conditions as biofouling occurred. The value of J at 1.5MPawas retained at just 58% of J0 after 24 h of the biofouling experiment, while that at 0.75 MPa was retained at about 77%. The increase of TMP enhanced the reduction rate in J. The value of J0 increased with increasing TMP (Fig. S2, details in Supplementary data). It is well known that a higher permeate flux results in increased severity of biofouling [14,17]. The increase in J would increase the drag force and CP on the membrane surface leading to transport of bacteria and nutrients, resulting in the faster biofilm development. Fig. 4A to D shows the analyzed CLSM images of stained bacteria on membrane surfaces after 24 h of the biofouling experiments at different TMPs. At the TMP of 0.75 MPa, bacteria that covered the membrane