Optimal Hydrogen Production Coupled with Pollutant Removal from Biodiesel Wastewater Using a Thermally Treated TiO2 Photocatalyst (P25): Influence of the Operating Conditions

This work aimed to produce hydrogen (H₂) simultaneously with pollutant removal from biodiesel wastewater by photocatalytic oxidation using a thermally-treated commercial titanium dioxide (TiO₂) photocatalyst at room temperature (~30 °C) and ambient pressure. The effects of the operating conditions, including the catalyst loading level (1-6 g/L), UV light intensity (3.52-6.64 mW/cm²), initial pH of the wastewater (2.3-8.0) and reaction time (1-4 h), on the quantity of H₂ production together with the reduction in the chemical oxygen demand (COD), biological oxygen demand (BOD) and oil and grease levels were explored. It was found that all the investigated parameters affected the level of H₂ production and pollutant removal. The optimum operating condition for simultaneous H₂ production and pollutant removal was found at an initial wastewater pH of 6.0, a catalyst dosage of 4.0 g/L, a UV light intensity of 4.79 mW/cm² and a reaction time of 2 h. These conditions led to the production of 228 μmol H₂ with a light conversion efficiency of 6.78% and reduced the COD, BOD and oil and grease levels by 13.2%, 89.6% and 67.7%, respectively. The rate of pollutant removal followed a pseudo-first order chemical reaction with a rate constant of 0.008, 0.085 and 0.044 min-1 for the COD, BOD and oil and grease removal, respectively.