Effect of the shear intensity on fouling in submerged membrane bioreactor for wastewater treatment

Air sparging is widely used to minimize membrane fouling within submerged membrane bioreactor (SMBR) applied to wastewater treatment. This paper discusses its effectiveness in hollow-fibre membrane modules and its relationship with permeate flux, backwashing frequency and duration and main biomass characteristics. The effect of air sparging is expressed as shear intensity G which enables to describe the influence of several hydrodynamic parameters (viscosity, air sparging area and air flow-rate) on membrane fouling. The experimental study was carried out with sludge at four different biomass concentrations (MLSS = 4100–14,500 mg l−1) filtered under a broad range of hydrodynamic conditions (J = 20–63 l h−1 m−2; G = 0–375 s−n). Under constant filtration conditions, the slope of TMP against time, the fouling rate, is described by an exponential function of G  : rf=(rf)0 exp−(FGG)+(rf)lrf=(rf)0 exp−(FGG)+(rf)l, where shear intensity sensitivity factor (FG) enables quantification of effectiveness of air sparging and limit fouling rate (rf)l describes the fouling caused by adsorption of micro-colloidal and soluble fractions over the external membrane surface. Also, it has been found that this sensitivity factor is a decreasing function of the imposed permeate flux and the biomass concentration.