This study investigated treatment of real liquid effluent generated from hydrothermal carbonization (HTC) of macadamia nut shell by employing transition metals Cu, Ni, and Fe doped titanium dioxide (TiO2) photocatalysts. The anatase TiO2 based photocatalysts were prepared via sol-gel method, and calcined at 400 °C. The modification with metal dopants was performed via ultrasonic assisted incipient wetness impregnation method. The prepared photocatalysts were characterized using XRD, UV-Vis DRS, SEM-EDX, and N2 physisorption. The influence of metal dopants, types of TiO2 support, and initial pH of the wastewater on the photocatalytic degradation performance of total organic carbon (TOC) and chemical oxygen demand (COD) in the wastewater were investigated. The results revealed that Fe doped TiO2 exhibited the highest photocatalytic activity followed by Cu and Ni, respectively. Among all, Fe doped anatase TiO2 were the most promising catalyst as it performed the highest removal of 75.1% for TOC and 94.1% for COD after 1 h irradiation at pH 4, achieving the lowest TOC and COD concentration of 405.62 mg/L and 91.26 mg/L, respectively. The findings suggested that photocatalytic degradation of HTC liquid effluent could be a potential treatment before releasing the wastewater to the environment.
Keywords: Advanced oxidation process; hydrothermal carbonization; photocatalysis; transition metal; treatment; wastewater.