Kim Hoong Ng

A novel photomineralization of POME over UV-responsive TiO2 photocatalyst: kinetics of POME degradation and gaseous product formations

Traditionally, palm oil mill effluent (POME) is treated via open ponding system, which however is land-intensive and requires long hydraulic retention time. For the first time, this paper reports, simultaneously, the kinetics of photocatalytic degradation of POME and the assessment of its gaseous product formations. Characterization of the as-received UV-responsive TiO2 showed that anatase was the predominant crystalline phase with an estimated crystallite size of 45.7 nm and band gap energy of 3.15 eV based on the UV-vis DRS scanning. Moreover, N2-physisorption revealed that the BET specific surface area for TiO2 was 8.73 m2 g−1 with pore size of 22.4 nm. When the photoreactor was blanketed with N2 gas only at a TiO2 loading of 0.5 g L−1, POME degradation was only 4%. Significantly, in the presence of O2, the degradation of POME achieved 23%, and can even attain a maximum of 52.0% at TiO2 loading of 1.0 g L−1 after 240 min of UV-irradiation. This has demonstrated that the hydroxyl generation rate from water species (prevalent in N2-blanket) was considerably slower compared to the hydroxyl generation from the superoxide pathway that originates from externally-supplied O2. It was also found that the POME degradation kinetics adhered to the 1st-order reaction with specific reaction rates (k) ranging from 0.70 × 10−3 to 2.90 × 10−3 min−1. Interestingly, our assessment of the gaseous product formations revealed that the photoreaction employing 1.0 g L−1 TiO2 produced the highest amount of CO2 (38 913 μmol) while 0.5 g L−1 TiO2 produced the highest amount of CH4 (361 μmol). From the FTIR scanning of used catalyst, we can confirm that the chemisorption of organics was practically absent. This has led us to believe that the primary role of TiO2 was to generate hydroxyls for direct attack on the organic compounds in the POME and eventually decompose them into simpler intermediates, CH4, CO2, and water. Moreover, after 20 h under the UV irradiation, POME degradation attained 78.0% and the final COD level dropped to 37 ppm, which is safe to be discharged.

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.