Meng Nan Chong

Nanostructured Tungsten Trioxide Thin Films Synthesized for Photoelectrocatalytic Water Oxidation: A review

The recent developments of nanostructured WO3 thin films synthesized through the electrochemical route of electrochemical anodization and cathodic electrodeposition for the application in photoelectrochemical (PEC) water splitting are reviewed. The key fundamental reaction mechanisms of electrochemical anodization and cathodic electrodeposition methods for synthesizing nanostructured WO3 thin films are explained. In addition, the effects of metal oxide precursors, electrode substrates, applied potentials and current densities, and annealing temperatures on size, composition, and thickness of the electrochemically synthesized nanostructured WO3 thin films are elucidated in detail. Finally, a summary is given for the general evaluation practices used to calculate the energy conversion efficiency of nanostructured WO3 thin films and a recommendation is provided to standardize the presentation of research results in the field to allow for easy comparison of reported PEC efficiencies in the near future.

Photocatalytic treatment of high concentration carbamazepine in synthetic hospital wastewater

Effective and sustainable treatment of hospital wastewater containing high concentration of pharmaceutical compounds presents a pivotal challenge to wastewater and environmental engineers worldwide. In this study, a titanium dioxide (TiO(2)) nanofiber based wastewater treatment process was assessed as a pre-treatment system to treat and enhance the biodegradability of a representative pharmaceutical compound, 5000 μg/L of carbamazepine (CBZ), in synthetic hospital wastewater. Results showed that the stand-alone TiO(2) pre-treatment system was capable of removing 78% of CBZ, 40% of COD and 23% of PO(4) concentrations from the influent wastewater within a 4h reaction time. High performance size exclusion chromatography demonstrated that a simultaneous biodegradability enhancement of hospital wastewater was observed, whereby an apparent shift in molecular weight from higher fraction (>10-1000 kDa) to a lower fraction (<10 kDa) was induced after 0.5h of photocatalytic treatment. Eventually, it was found that the photodegradation profile for high concentration CBZ in synthetic hospital wastewater was perfectly fitted to the Langmuir-Hinshelwood kinetics model. It is anticipated that this TiO(2) pre-treatment process can be further integrated with a biological wastewater treatment process to deliver treated hospital effluent of better quality that can minimise the associated human health and environmental risks.

An integrated MBR-TiO2 photocatalysis process for the removal of Carbamazepine from simulated pharmaceutical industrial effluent.

This paper aims to demonstrate that integrating biological process and photocatalytic oxidation in a system operated in recycling mode can be a promising technology to treat pharmaceutical wastewater characterized by simultaneous presence of biodegradable and refractory/inhibitory compounds. A lab-scale system integrating a membrane bioreactor (MBR) and a TiO(2) slurry photoreactor was fed on simulated wastewater containing 10mg/L of the refractory drug Carbamazepine (CBZ). Majority of chemical oxygen demand (COD) was removed by the MBR, while the photocatalytic oxidation was capable to degrade CBZ. CBZ degradation kinetics and its impacts on the biological process were studied. The adoption of a recycling ratio of 4:1 resulted in removal of up to 95% of CBZ. Effluent COD reduction, sludge yield increase and respirometric tests suggested that the oxidation products were mostly biodegradable and not inhibiting the microbial activity. These results evidenced the advantages of the proposed approach for treating pharmaceutical wastewater and similar industrial effluents.

Bathroom greywater recycling using polyelectrolyte-complex bilayer membrane: Advanced study of membrane structure and treatment efficiency.

Polyelectrolyte-complex bilayer membrane (PCBM) was fabricated using biodegradable chitosan and alginate polymers for subsequent application in the treatment of bathroom greywater. In this study, the properties of PCBMs were studied and it was found that the formation of polyelectrolyte network reduced the molecular weight cut-off (MWCO) from 242kDa in chitosan membrane to 2.71kDa in PCBM. The decrease in MWCO of PCBM results in better greywater treatment efficiency, subsequently demonstrated in a greywater filtration study where treated greywater effluent met the household reclaimed water standard of <2 NTU turbidity and <30ppm total suspended solids (TSS). In addition, a further 20% improvement in chemical oxygen demand (COD) removal was achieved as compared to a single layer chitosan membrane. Results from this study show that the biodegradable PCBM is a potential membrane material in producing clean treated greywater for non-potable applications.

Sol-Gel Synthesis of Inorganic Mesostructured Composite Photocatalyst for Water Purification: An Insight Into the Synthesis Fundamentals, Reaction, and Binding Mechanisms

The paper discusses the sol-gel synthesis of an inorganic mesostructured composite photocatalyst for application in water purification. The fundamentals for each synthesis step on the final Ti-content, anatase-to-rutile composition, bonding structure and mechanism to kaolinite, shape, surface area, and size control were described. In addition, various advanced microscopic techniques were used to characterize and validate the physical and chemical properties of the composite photocatalyst. A hypothetical schematic for the fabrication of mesostructured composite photocatalyst was also presented to better illustrate the overall reaction and binding mechanism. The photocatalytic degradation of an aqueous dye solution was also investigated.

Computational Fluid Dynamics Modelling of Photoelectrocatalytic Reactors for the Degradation of Formic Acid

In this study, computational fluid dynamics (CFD) simulation was used to predict the performance of photoelectrocatalytic (PEC) reactors with surface reactions. PEC process is a promising and sustainable method that is capable for simultaneous organic degradation and hydrogen production. However, the overall PEC process efficiency is still unsatisfactory and not ready for scale-up application. Preliminary study using CFD model can help to reduce development time, money and effort in experimental work while providing comprehensive analysis and optimum PEC reactor design prior to its real physical fabrication. CFD model integrates irradiance distribution, hydrodynamics, species mass transport and chemical reaction kinetics within the reactor. The performance of PEC reactor for organic degradation depends on reactor configurations and hydrodynamic conditions. Thus, the main aim of this study was to optimize different PEC reactor designs using CFD modelling by varying the reactor configurations and hydrodynamic flow conditions for improved efficiency in degrading the sample organic pollutant of formic acid. The CFD modelling showed higher formic acid degradation efficiency for the simulated convex surface photoreactor than the flat surface photoreactor due to the former possess the ability to concentrate the absorbed light onto the photoanode surface. Besides, the CFD modelling showed that the formic acid degradation rate increased with decreasing inlet fluid flow velocity. This was due to the uniform flow distribution that enables evenly coverage of photoanode surface for subsequent degradation of formic acid in the PEC reactors. Further experimental work is required to validate the CFD simulation to allow better understanding and improvement of the overall efficiency of PEC reactors.