Flocculation–microfiltration integration for high-salinity oilfield offshore produced water treatment

This study evaluated an integrated treatment system that combines chemical destabilization (through flocculation) with membrane-based separation (via submerged microfiltration) for removing of dispersed oil from oilfield produced water (OPW) under realistic salinity and temperature conditions. Both synthetic and real OPW emulsions were treated using polymeric flocculants, followed by the submerged-MF employing 0.1 μm tubular and flat sheet ceramic membranes at 60 ℃. System performance was assessed in terms of total oil and grease (TOG) removal and permeate flux. Fouling mechanisms were analyzed using Hermia models alongside a Python®-based numerical simulation, fitting the empirical resistance decay via nonlinear optimization. The use of the commercial anionic flocculant HYPERFLOC^TM AE 120 led to TOG removal efficiencies up to 85% in synthetic emulsions prepared with 100 g/L NaCl at 60 ℃. The integrated flocculation/submerged-MF process ensured full compliance with offshore discharge regulations for produced water. Membrane configuration strongly influenced performance; flat sheet membranes exhibited milder flux decline and superior flux recovery after cleaning, while tubular membranes were prone to pore-blocking. In contrast, cake layer formation was more prominent in flat membranes. Empirical exponential decay models provided the best fit for resistance evolution (R² = 0.996), surpassing the accuracy of the mechanistic Hermia models in describing fouling behavior. For oilfield produced water emulsions, flocculation was less efficient due to the matrix complexity. However, submerged-MF significantly reduced TOG content and turbidity. Overall, the engineered integrated system demonstrated robustness and scalability potential for OPW treatment in challenging offshore environments, highlighting the benefits of process synergy and operational adaptability.