Influence of hydrodynamics on fouling velocity in a recirculated MBR for wastewater treatment

Membrane fouling within membrane bioreactor (MBR) applied to wastewater treatment was studied under adequate recirculation conditions, for which fouling was only caused by soluble and colloidal fractions of the biological suspension. Four different activated sludges under steady-state biological conditions were tested under a wide range of hydrodynamic conditions (U=2-5 m/s; Re=3000-20000; J=40-250 l/h m(2)). With constant filtration conditions, the increase in hydraulic resistance with time (dR/dt) was measured as the "fouling velocity", and this varied according to hydrodynamic and biological conditions. Two different models were established to describe this influence, in the form of ln partial derivative R/theta t = p - q chi. The first model, with the hydrodynamic parameter chi = Re(0.8)tau(0)/rho J(2), was based on an energy comparison between the shear forces, represented by tau(0), and the kinetic energy linked to the permeation flux described by rho J(2). The second one, with chi = Re-1.3/J d(h), was based on a description of the mass transfer around the membrane, using equations based on adimensional parameters. (C) 1999 Elsevier Science B.V. All rights reserved.