A combined mechanism (the open pores-cake dissolution) model for describing the trans-membrane pressure (Pb(t)) reduction in the backwash process at a constant flow rate

Abstract

Accurate prediction of the trans-membrane pressure (Pb(t)) reduction in the backwash process at a constant flow rate has a great significance for the industrial backwash process. In this paper, a combined mechanism (the open pores-cake dissolution) model was established to predict the variation of Pb(t) in the backwash process at a constant flow rate for 0.1 µm polyacrylonitrile (PAN) membrane fouled with activated sludge suspension. Meanwhile, the proposed model was validated by using other foulants (yeast, bovine serum albumin and sodium alginate), membranes (0.1 µm polyethersulfone (PES) and polyvinylidene fluoride (PVDF) membranes) and at different fouling conditions (filtrate flow rate, mixed liquor suspended solid (MLSS) concentration and cross-flow velocity). The results showed that the model predictions were in good agreements with experimental data (R2>0.986, relative error σ¯ <3.28%). Moreover, according to the variation of Pb(t), the backwash process can be divided into three stages: (i) Pb(t) decreased rapidly (the open pores-cake dissolution) before ti (the first transition point); (ii) Pb(t) decreased slowly (cake dissolution) in the range of ti to tj (the second transition point); (iii) Pb(t) is almost constant (without the open pores and cake dissolution) after tj. Thus, the proposed model would provide a theoretical basis for achieving the goal of high-efficient and energy-saving in the backwash process at a constant flow rate.