Influence of relaxation frequency on membrane fouling control in submerged anaerobic membrane bioreactor (SAnMBR)

The effect of different intermittent filtration modes on membrane fouling was investigated in a submerged anaerobic membrane bioreactor treating palm oil mill effluent. The filtration was operated at the range of supra critical conditions (permeate flux equal to 20 Lm(-2) h(-1)), and the submersed membranes were continuously cleaned by gas injection and intermittent periods of relaxation. Four conditions of relaxation (S1: 240 s filtration/30 s relaxation, S2: 480 s filtration/30 s relaxation, S3: 720 s filtration/30 s relaxation, and S4: 960 s filtration/30 s relaxation) were analyzed by comparing the trans-membrane pressure evolution rates, the main fouling origins, and the content of membrane cleaning solutions in terms of proteins and carbohydrates. Results showed (i) the dominant effect of the cake deposit (50% of the total hydraulic resistance) whatever the relaxation frequency, (ii) the equivalent importance of pore blocking and adsorption, and (iii) the clear interest of working with the highest relaxation frequencies to limit the specific hydraulic resistance (50 times lower in comparison with low relaxation frequencies). Moreover, the presence of SMP and EPS was found in the different cleaning solutions confirming their determining role in fouling mechanisms.