Hybrid TiO2/UV/PVDF ultrafiltration membrane for raw canola oil wastewater treatment

Abstract

Polymeric ultrafiltration (UF) membranes have been applied to treat raw canola oil wastewater (COW); however, membrane fouling was unavoidable. To solve this issue, this study examined sole UF, hybrid Fenton/UV/UF and TiO2/UV/UF to investigate membrane fouling, which has the effect of decreasing membrane filtration performance. The experimental results showed that, of three methods, the hybrid TiO2/UV-UF system significantly increased the permeation flux value, with chemical oxygen demand (COD) and oil removal efficiencies increased by 82 and 86%, respectively. This hybrid system was further explored under different transmembrane pressures (TMP)-1, 2, and 3 bar-and cross flow velocities (CFV)-400, 500, and 600 mL/min. Hermia’s model was used to analyse the fouling mechanism; no model acted as the main mode, with nearly similar values of cake formation and other models regardless of the applied conditions. Membrane surface morphology and foulant composition were explored using scanning electron microscopy and energy dispersive spectrometry (SEM-EDS), demonstrating significantly different morphologies and chemical components between new and fouled membranes due to the trapped oil and other micro-pollutants on the membrane surface and pores. The effect of using different cleaning agents on membrane cleaning was also evaluated by measuring the flux recovery ratio (FRR). This study found that a combined chemical cleaning agent (0.1 M NaOH/0.1 M HNO3) at elevated temperature and higher velocity resulted in a higher FRR value, by at least 97%. In conclusion, both the hybrid TiO2/UV-UF method and combined chemical cleaning can be applied to treat raw COW to reduce fouling and lengthen membrane life.