Optimization of photocatalytic degradation of palm oil mill effluent in UV/ZnO system based on response surface methodology

This paper reports on the optimization of palm oil mill effluent (POME) degradation in a UV-activated-ZnO system based on central composite design (CCD) in response surface methodology (RSM). Three potential factors, viz. O₂ flowrate (A), ZnO loading (B) and initial concentration of POME (C) were evaluated for the significance analysis using a 2³ full factorial design before the optimization process. It is found that all the three main factors were significant, with contributions of 58.27% (A), 15.96% (B) and 13.85% (C), respectively, to the POME degradation. In addition, the interactions between the factors AB, AC and BC also have contributed 4.02%, 3.12% and 1.01% to the POME degradation. Subsequently, all the three factors were subjected to statistical central composite design (CCD) analysis. Quadratic models were developed and rigorously checked. A 3D-response surface was subsequently generated. Two successive validation experiments were carried out and the degradation achieved were 55.25 and 55.33%, contrasted with 52.45% for predicted degradation value.