Modelling the critical roles of zeta potential and contact angle on colloidal fouling with a coupled XDLVO - collision attachment approach

A coupled XDLVO-collision attachment (CA) model is proposed to quantitatively evaluate the critical roles of zeta potential ζ and contact angle θ of foulant on colloidal fouling. In this model, the XDLVO theory is applied to relate ζ and θ to foulant-membrane interaction energy barrier (ΔEb). The latter is further bridged to membrane fouling rate (dmf/dt) by the CA theory, recognizing fouling as foulant colliding with a membrane surface followed by its attachment. XDLVO-CA model predictions agree well with the experimental water flux declines under various solution pHs. Modelling results show that severe fouling occurs at low ζ2, and increasing ζ2 can substantially lower dmf/dt as a result of the increased ΔEb. Interestingly, a negative linear relationship is observed between ζ2 and logarithm of dmf/dt at high ζ2. For the role of contact angle for water, glycerol and diiodomethane, there exists a critical θ, below (or above) which little fouling occurs owing to the dramatically increased ΔEb and thus decreased dmf/dt by orders of magnitude. Furthermore, the threshold θ corresponds to the acid-base interaction energy transiting from attraction to repulsion. Our modelling results reveal the importance of optimally tailoring foulant ζ and θ for fouling control.