Добірка наукової літератури з теми "Photocatalytic MF membrane"

Humic acids (HA) that are one of the major organic components in natural water play an important role in water treatment because they can interact with metals, trace organics, and chlorine while generating toxic complexes and by-products. In this work, photocatalytic degradation of HA and its kinetic behavior were investigated in a photocatalytic microfiltration (MF) system, along with evaluation of membrane permeability at different fluxes. The mechanisms of adsorption and desorption of HA on TiO2 surfaces were elucidated with adsorption isotherm tests of HA before and after photocatalysis of humic water. The kinetic parameters for humic acids, k (rate constant) and K (equilibrium adsorption coefficient) of the Langmuir-Hinshelwood equation, were obtained based on mass balances in continuous stirred tank reactor (CSTR) operations. Regarding membrane fouling, it was assumed that the rate of degree of fouling is disproportional to the fouling resistance. It was found that the fouling rate constant started increasing substantially when the flux increased to a level of greater than 50 L/m2-h. This indicated that the photocatalytic MF system should be operated at a flux below the critical value to prevent serious membrane fouling.

The approach of the present work is based on the use of poly (methylmethacrylate) (PMMA) polymer, which is compatible with PVDF and TiO2 nanoparticles in casting solutions, for the preparation of nano-composites membranes using a safer and more compatible solvent. TiO2 embedded poly (vinylidene fluoride) (PVDF)/PMMA photocatalytic membranes were prepared by phase inversion method. A non-solvent induced phase separation (NIPS) coupled with vapor induced phase separation (VIPS) was used to fabricate flat-sheet membranes using a dope solution consisting of PMMA, PVDF, TiO2, and triethyl phosphate (TEP) as an alternative non-toxic solvent. Membrane morphology was examined by scanning electron microscopy (SEM). Backscatter electron detector (BSD) mapping was used to monitor the inter-dispersion of TiO2 in the membrane surface and matrix. The effects of polymer concentration, evaporation time, additives and catalyst amount on the membrane morphology and properties were investigated. Tests on photocatalytic degradation of methylene blue (MB) were also carried out using the membranes entrapped with different concentrations of TiO2. The results of this study showed that nearly 99% MB removal can be easily achieved by photocatalysis using TiO2 immobilized on the membrane matrix. Moreover, it was observed that the quantity of TiO2 plays a significant role in the dye removal.

The purpose of this study is to investigate the effect of the operational parameters of the UV intensity and TiO2 dosage for the removal of humic acid and heavy metals. It also evaluated the applicability of hollow fiber microfiltration for the separation of TiO2 particles in photocatalytic microfiltration systems. TiO2 powder P-25 Degussa and hollow fiber microfiltration with a 0.4 μm nominal pore size were used for experiments. Under the conditions of pH 7 and a TiO2 dosage 0.3 g/L, the reaction rate constant (k) for humic acid and heavy metals increased with an increase of the UV intensity in each process. For the UV/TiO2/MF process, the reaction rate constant (k) for humic acid and Cu, with the exception of Cr in a low range of UV intensity, was higher compared to that of UV/TiO2 due to the adsorption of the membrane surface. The reaction rate constant (k) increased as the TiO2 dosage increased in the range of 0.1~0.3 g/L. However it decreased for a concentration over 0.3 g/L of TiO2. For the UV/TiO2/MF process, TiO2 particles could be effectively separated from treated water via membrane rejection. The average removal efficiency for humic acid and heavy metals during the operational time was over 90 %. Therefore, photocatalysis with a membrane is believed to be a viable process for humic acid and heavy metals removal.

TiO2 photocatalytic oxidation was combined with microfiltration (MF) (PCOMF) to remove humic acid (HA) in waters through investigating the flux performance, TOC, UV254 and UV436 removal efficiency, the fouled membrane surfaces by SEM. The results demonstrated that the combined PCOMF process showed a high removal efficiency of UV254 and UV436 of HA (close to 100%). The removal efficiency of TOC was about 84.34% indicating that most of HA was mineralized into water and carbon. The SEM images witnessed that the fouling on the membrane surfaces contaminated by PCO effluents after UV254 and UV365 light irradiation was mainly attributed to cake layer, which was reversible due to the increase of aggregated particles size consisting of HA and TiO2. Eventually, the combined PCOMF process displayed an improved effect on HA removal and fouling control to a certain level.

Membrane filtration has revolutionised water treatment, enabling safer provision of drinking water due to its high efficiency to block human infectious pathogens commonly present in raw water sources. Accumulation of substances on membrane surfaces and pores during operation, referred to as fouling, is considered one of the biggest barriers to wider adoption of membrane technology in water treatment. Maintaining continuous low-pressure filtration requires significant amounts of chemicals to clean off the accumulated fouling substances. Chemical use comes with economic and environmental costs associated with acquisition, transportation, storage, usage and disposal of chemicals, especially in disadvantaged and remote communities. By conservative estimates, supply of household water to a remote community of 100 people using a membrane system would require continuous supply of at least 10 L of polyaluminium chloride coagulant and 4 L of sodium hypochlorite (in concentrated form) every month. The main aim of this thesis is to demonstrate a sustainable, innovative, low cost membrane solution harnessing conveniently available solar energy to offset these chemical demands. Coating membrane substrates with semiconductor photocatalysts such as titanium dioxide (TiO2) is an effective method for mitigating fouling in membranes through induced superhydrophilicity, enabling cleaning from the available water without chemicals. TiO2 also enables water contaminant degradation and pathogen inactivation through reactive oxygen species (ROS) facilitated advanced oxidation. Despite these well- known effects, a major challenge limiting practical adoption comes from light absorption and scattering by the turbid contaminants in the feed stream before reaching the TiO2. This thesis proposed a novel solution to this challenge by transmitting light to the TiO2 through cheap porous borosilicate glass substrates with between 10% and 80 % transmission in the 340-400 nm wavelength range relevant to activating commercial Degussa P25 TiO2 photocatalyst. The concept novel membrane was produced using commercial glass substrates modified by simply dip- coating and heat sintering Degussa P25. The formed asymmetric membrane’s mean pore size was measured at 0.5 μm, which classifies the membrane as a microfiltration (MF) membrane, which are utilised in the industry as a barrier to water-borne pathogens such as protozoa and bacteria, and partially to viruses. To demonstrate the membrane’s photocatalytic ability, photocatalytic reactions stimulated by a UV lamp (365 nm peak) facing the glass substrate side in an ex-situ setup led to a 52% degradation of methyl orange in aqueous solution, being only slightly lower than the 58% degradation when the TiO2 active layer faced the UV light source. The membrane was then operated in-situ using a custom module with a quartz window and UV LED installed on the permeate side, enabling simultaneous microfiltration of model fouling solutions. Results showed significant reductions in trans-membrane pressure (TMP) rise rates directly linked to UV light application. Specifically, UV light was responsible for up to 3.0-fold reduction in total filtration resistance and up to 4.2-fold reduction in irreversible fouling indices. Testing continued on simulated indirect solar light with a real non-potable water. The membrane itself showed up to 94% turbidity removal and up to 80% total organic carbon (TOC) rejection. The sunlight was directly responsible for an 8-fold reduction in the irreversible fouling index. The significant practical findings were followed by an investigation to confirm the fundamental basis for improvement. Analysis by scanning electron microscopy (SEM) coupled with fouling modelling showed the beneficial photocatalytic fouling reduction effects during microfiltration stemmed from reduced intrusion of organic fouling material inside the TiO2 membrane pores, as well as reduced cake layer resistance. Analysis of results and photocatalysis mechanisms from literature led to the conclusion this was due to both superhydrophilicity minimising organic attractions to the surface and photocatalytic oxidation of organics approaching the surface. The potential for advanced oxidation to participate in reacting with organic matter surfaces attracted to the membrane was confirmed from a measurable increase in the presence of hydroxyl radicals using para-chlorobenzoic acid (pCBA) probe experiments. The practical benefits for industry towards chemical consumption and energy reduction were also measured. For example, a 4.5-fold extension to the time needed for a clean-in-place (CIP) was realised when the membrane was operated in photocatalytic mode. A 50% reduction in filtration pump electricity demand was also calculated, which translates to a reduction in height of the feed water for a flux of 300 L/m2/h from 8.6 m to 3.7 m over a 5 hour run. Future work suggested includes using recycled glass to improve affordability and minimise glass manufacture environmental impact, as well as experimentally establishing the relationship hydroxyl radical concentration and TOC reduction. Optimisation of the glass material for enhancing light transmission efficiency and development of porous glass monoliths like current commercial ceramic membranes for full-scale use, as well as optimisation to increase contaminant degradation are also suggested.