Stochastic Collision-Attachment-Based Monte Carlo Simulation of Colloidal Fouling: Transition from Foulant-Clean-Membrane Interaction to Foulant-Fouled-Membrane Interaction

The initial behavior of colloidal fouling is governed by foulant-cleanmembrane interaction (F-M), and its long-term behavior is determined by foulantfouled-membrane interaction (F-F). Nevertheless, the transitional fouling behavior from F-M to F-F has not been fully understood. This study reports a novel collision attachment (CA)-Monte Carlo (MC) approach, with the stochastic colloidmembrane collision events modeled by MC and the probability of colloidal attachment to the membrane determined by the interplay of flux and the energy barrier arising from colloid-membrane interaction (E-m for F-M and E-f for F-F). The long-term membrane flux remains stable for large E-f, whereas severe fouling occurs when both E-m and E-f are small. Our study reveals the existence of a metastable flux behavior for the combination of large E-m but small E-f. The time evolution of flux behavior and colloidal deposition patterns shows a nearly constant flux for an extended period, with the high energy barrier E-m retarding initial colloidal deposition. However, accidental random deposition of a colloidal particle could reduce the local energy barrier (toward the smaller E-f), seeding for further colloidal deposition in its vicinity. This initiates an uneven patch-wise fouling and eventually leads to a complete transition to F-F-dominated behavior. The metastable period can be effectively extended by increasing the energy barrier (E-m or E-f) or lowering flux, which provides important implications to membrane design and operation.