Original Contribution to the Theory of Membrane Fouling in Produced Water Treatment: Integration of Colloidal Interaction Forces with Hydrodynamic Models for Niger Delta Produced Water

Membrane fouling is the principal operational constraint limiting the economic viability of membrane-based produced water treatment for offshore Niger Delta applications, and existing fouling theory fails to account for the unique colloidal composition of Niger Delta produced water, which contains high concentrations of naturally occurring radioactive material scaling compounds, divalent ion-stabilised emulsions, and asphaltenic residuals. This study makes an original theoretical contribution by developing an extended Derjaguin-Landau-Verwey-Overbeek interaction energy model incorporating specific ion effects, non-DLVO hydrophobic attraction forces, and asphaltene particle viscoelastic properties calibrated for Niger Delta produced water chemistry. The extended model is coupled with a modified cake filtration transport model incorporating Bingham plastic cake layer rheology, derived from the observation that Niger Delta produced water fouling layers exhibit yield stress behaviour absent from existing models. Theoretical framework development was supported by atomic force microscopy force-distance measurements using probe tips functionalised to mimic polysulfone membrane surfaces interacting with produced water colloidal particles. Model predictions of initial flux decline rate, critical flux, and steady-state rejection were validated against crossflow ultrafiltration experiments using produced water samples from four Niger Delta fields. The integrated model predicted fouling behaviour more accurately than existing models, with a 30 to 45% improvement in flux prediction root mean square error. The study establishes a new theoretical paradigm for membrane fouling prediction in produced water treatment systems that explicitly incorporates the physicochemical complexity of Niger Delta produced water. Keywords: membrane fouling theory, produced water, DLVO, Niger Delta, colloidal interactions