Pre-coagulation with novel titanium coagulants for mitigating membrane fouling in direct membrane filtration of municipal wastewater

Direct membrane filtration (DMF) is regarded as a promising technology for municipal wastewater treatment owing to its advantages of carbon recovery and compactness. However, its application is limited by severe membrane fouling caused by high levels of colloidal and soluble organics in municipal wastewater. Polytitanium chloride (PTC) and titanium xerogel coagulant (TXC), both prepared from TiCl4, were employed in this study to rapidly pre-coagulate wastewater to reduce the burden of filtration, mitigate membrane fouling, and achieve sustained system operation. The hybrid coagulation-DMF (C-DMF) processes with Ti-based coagulants successfully removed over 80 % COD and 95 % turbidity and reduced the average TMP growth rate from 13.70 kPa/h to 0.026-0.072 kPa/h while controlling the increase in reversible and irreversible resistance. PTC demonstrated a stronger ability to neutralize charges at pH <= 4, whereas TXC was more effective at a broader pH range and exhibited superior sweeping capabilities at high pH levels. As a result of higher COD removal in the supernatant and lower attractive interaction energy between the membrane and pollutants at the minimum separation distance, PTC (30 mg Ti/L) performed better in three stages of C-DMF. This study demonstrated the feasibility and superiority of rapid coagulation using Ti coagulant as a pretreatment for DMF, providing an alternative solution for resource-based treatment of municipal wastewater.