Short-term fouling control by cyclic aeration in membrane bioreactors for cosmetic wastewater treatment

Air sparging is extensively used to mitigate membrane fouling in membrane bioreactors (MBRs), which represents an important operation cost in submerged MBR. In this work, the effect of intermittent aeration mode on the membrane fouling has been studied by analysing the influence of the aeration cycle duration in a submerged MBR treating cosmetic wastewater. The long-term filtration at a permeate flux of 8.0Lm(-2)h(-1) and a constant specific air demand (SAD) of 1.5m(3)m(-2)h(-1) led to a significant increase in the transmembrane pressure (TMP) after 10d. The tangential shear showed a limited effect on preventing the deposition of small particles, since carbohydrates and proteins present in the fouling layer were mainly smaller than 1m. Flocs showed a low stability under shear stress, which limits the increase in the SAD to avoid undesirable effects over the mixed liquor permeability. The intermittent aeration operation allowed the operation of the MBR under low aeration intensity (low SAD) without compromizing the fouling of the membranes. The use of aeration cycles shorter than 1min led to an efficient control of fouling, which resulted in a negligible increase in the TMP after 2h, operating at a permeate flux of 12.0Lm(-2)h(-1).