Photocatalytic Treatment of Real Sugar Industry Wastewater Using Lignocellulosic Biomass-Derived Hydrochar/g-CN

Hydrochar obtained from biomass via hydrothermal carbonization (HTC) was employed as a supporting material to enhance the photocatalytic activity of graphitic carbon nitride (g-CN). To the best of our knowledge, this is the first study combining sugar beet pulp-derived hydrochar with g-CN for photocatalytic treatment of real sugar industry wastewater, representing a circular economy approach where the solid waste of the sugar industry is valorized to treat its own liquid effluent. HTC process conditions were systematically optimized through Box-Behnken design with a second-order polynomial response surface model to examine the effects of temperature (200-260 °C), reaction time (60-120 min), and biomass amount (10-20 g). Operational parameters of pH (4-8), catalyst loading (0.2-1 g/L), and H₂O₂ (0-20 mM) were utilized during the optimization. The highest hydrochar yield (36.74%) was achieved at 200 °C for 60 min using 20g biomass. Under optimized photocatalytic conditions (0.81 g/L catalyst loading, pH 8, 20 mM H₂O₂), total organic carbon (TOC) removal efficiency reached 14.02%; the low removal rates are attributable to the exceptionally high initial TOC concentration (>7000 m/L), which far exceeds organic loads typically encountered in photocatalytic studies. Hydrochar incorporation improved the reusability and stability of the photocatalyst, enhancing resistance under complex wastewater matrix conditions. The results highlight the potential of biomass-derived hydrochar as a low-cost and sustainable strategy for improving photocatalytic treatment performance in industrial wastewater applications.