Volume 14 (2002)
Table of Contents
Table of Contents
Pulsed Electrophoretic Membrane Cleaning for Dead-End Ultrafiltration Process
Membrane separation technology has been identified as a new and clean technology and as an alternative to the conventional separation technology since it can offer some advantages over those separation technologies. Nevertheless, membrane fouling appears to be the major bottleneck of this technology. Many approaches have been proposed to reduce membrane fouling. The approach considered in this paper is the application of electric pulse to remove deposits from the membrane surface. An experimental test rig is constructed to study the effect of electric pulse on the membrane cleaning effectiveness. The filter cake is collected after every application of each electric pulse to ensure that the deposited materials which has been removed from the membrane surface after each electric pulse will not be redeposited onto the membrane surface. The dead-end ultrafiltration of silica dioxide (SiO2) dispersion is conducted with various values of pulse interval, pulse duration and feed concentration. It is found that the application of the electric pulse to reduce membrane fouling and restore high permeation rate is effective in the dead-end filtration process. The application of electric pulses across the membrane gives a higher permeation rate than the conventional ultrafiltration process.
Wastewater Treatment Using Photocatalysis: Destruction of Methylene Blue Dye from Wastewater Streams
Photocatalytic processes have been suggested as an alternative treatment for water pollutants. Although presently many treatment methods are being used, most of them do not completely destroy the pollutants but only offer phase transfer or partial degradation of the pollutants. In photocatalytic processes, a semiconductor photocatalyst is activated with ultraviolet (UV) irradiation. The activated photocatalyst promotes the formation of hydroxyl radicals, which in turn completely degrades the pollutants. In the present study, an ultraviolet irradiated photoreactor system was used to degrade methylene blue dye in aqueous solutions. The photocatalyst used was titanium dioxide (TiO2) Experiments were performed with varying catalyst loading, initial concentration of dye, circulation flow rate and air flow rate. Initial reaction rates of dye degradation were used to compare the effect of varying the above variables. The effect of increasing the catalyst loading from 0 to 0.4 wt% showed that an increase in the initial reaction rate, reaching an optimum at catalyst loading of 0.2 wt%. Effect of initial concentration has proven that lower initial concentration resulted in more efficient degradation of the dye. The increase in the initial reaction rate degradation with increasing circulation flow rate confirmed the significant role played by external mass transfer. Introduction of air to the system did not significantly increase in the initial reaction rate when the air flow rate was increased from 0 to 4.0 liter min-1.
Oxygen Transfer Rate in an Aerated Tank for Pharmaceutical Wastewater Treatment
The treatment of pharmaceutical non-penicillin wastewater was conducted in the biological aerobic process. The oxygen transfer rate played the major role to reduce the organic pollutants of the wastewater by removing gases, oils, volatile acids and odour. The microbial culture used in the experiment was the ethanol producers, isolated from the wastewater, optical density, COD and concentration of chemicals equivalent to carbohydrate were measured in a time period of 3-4 days of aeration. The propagation of bacteria was monitored and its growth rate was determined. Oxygen transfer rate and mass transfer coefficients were found to be affected by airflow rate, bubble size and agitation rate. Dissolved oxygen was shown as an indication of microbial growth and limitation of mass transfer: The dissolved oxygen was about 7.89 ppm from the starting point and then it dropped to 2 ppm by the end of the first day. After the second day of aeration the oxygen depletion was obviously observed since the DO meter showed 0.14 ppm. Aeration rate was 0.2 – 1.3 liters per minute for working volume of 3 liters and 5-10 liters per minute for 15 liters aerated tank. Maximum optical density was obtained with high aeration rate at the first day of aeration, 0.95 g/l, as the aeration was reduced the cell propagation was also reduced. The maximum cell growth was obtained by the end of 3 days of aeration with minimum airflow rate. The maximum COD and carbohydrate reduction was 58 and 90 percent respectively with 1.15 liter/min airflow rate in the 3 liters aeration system. The bubble size affected the mass transfer coefficient (KLa), as the contact surface of gas exposure to liquid increased the mass transfer coefficient was increased. As the dissolved oxygen concentration dropped the KLa was also decreased. The values of KLa for the 5 and 10 liters/min airflow rate for 15 liters aerated tank were 0.055 h- 1 and 0.3975 h-1 respectively.
Penghasilan Abu Sekam Padi Menggunakan Relau Terubahsuai UKM (Production of Rice Husk Ash Using UKM Modified Furnace)
The quality of rice husk ash, which is produced using specially designed furnace at Universiti Kebangsaan is studied. By using appropriate combustion technique, high content of silica ash was able to be produced. The furnace was fabricated and improved based on the previous concept adopted by Universiti Sains Malaysia and Asian Institute of Technology. Investigation is done to determine the physical and chemical properties including temperature distribution, particle size, crystallization phase and chemical composition. It was found that the specially designed furnace was able to produce a high quality of rice husk ash.
Extraction of Crude Palm Oil Using Supercritical CO2
The effects of changing the operating pressure and temperature on the solvating strength of supercritical carbon dioxide and the solubility of crude palm oil in the solvent were discussed. The operating temperatures and pressures investigated are 40, 50 and 60°C, and 110, 140 and 200 bars. Changes in pressure showed a stronger influence on palm oil solubility in CO2 compared to temperature. The rate of extraction and the solubility of palm oil increased when the system pressure was increased (at constant temperature) or when the system temperature was decreased (at constant pressure). These results are comparable with the reported results of solubility of other vegetable oils such as soybean and olive oils. The change in the physical behaviour and the colour of the oil extracts and residues were also observed. It was discovered that the initial fractions of palm oil extracted were solid like while the latter fractions were semi-liquid. As the extraction progressed, the orange colour of the fractions became progressively more intense at 200 bars. At lower pressures of 140 and 110 bars, however the colour intensity was reduced, indicating decreasing density and solvating strength of the supercritical CO2.
Time Dependent Dispersion in Macro Scale Heterogeneous Porous Media
Due to the difficulty of characterizing complex heterogeneities with mathematical equations, the analytical solution based on the convection-dispersion equation assumes dispersion that is independent of time and space. However, moreestablished results suggest that dispersion varies with space due to the complexity of a porous structure and the effect of large heterogeneities in the field. This space dependence of dispersion has been considered as the primary reason for the “scale-up” problem, which is disparity between laboratory and field measured dispersion. In this work, the space dependence of dispersion is converted to time dependence by considering the fact that distance x = nt and K(x) = (nt) = nK(t) since average velocity flow is considered. Results from this work demonstrate that space or time independence of dispersion only occurs at relatively long duration of flow where the flow is generally stabilized and small values of fractal exponent. The concentration profile in a porous system assuming constant and time dependent dispersion is also evaluated.
Reduction of NOx Emissions From Gas Turbine Combustor With Fuel Staging
A two stage lean/lean gas turbine combustor was developed with low NOx characteristics in each stage using small radial swirler of 40 mm outlet diameter in the pilot stage. Both flame tubes were arranged in series with the smaller combustor (76 mm inside diameter) as the pilot stage and the larger combustor (140 mm inside diameter) as the main stage. The pilot stage was fuelled via vane passage fuel injector; while the main stage was fuelled around the wall of the exit plane of the pilot stage, using wall fuel injectors. Ultra low NOx emissions as low as 15 ppm were obtained when using fuel staging for propane fuel. NOx reduction of 68% was obtained at equivalence ratio of 0.74, when using fuel staging compared to the non-fuel staging tests. This was achieved with small decrease in carbon monoxide emissions and no increase at all in the unburned hydrocarbon emissions at the same equivalence ratio.
General Algorithms for 3-D Motion of a Non-Planar Body in a Steady-State Force Field
Determining trajectories of objects in three-dimensional space is fundamental to many disciplines. Whether the objects be molecules or celestial bodies, the standard Newtonian equations of motion describe this dynamic behavior. Unfortunately, however the complexity of a real system normally requires that the equations of motion be solved numerically and methods presented in classical mechanics textbooks are of little practical use. In addition, the standard equations of motion involving Eulaer angles contain singularities and are therefore not suitable for computer solution. This paper discusses implementation of two powerful but little known techniques using quaternions, the Evans and the Rapaport methods. These little known techniques have been developed by and used for molecular modeling, but their application is far reaching, and can be applied to any system where quantum or relativistic effects may be neglected. These methods shoe excellent conservation of energy over many millions of time steps and are free of singularities. Herein we compare the two methods in terms of efficiency and accuracy. Due to their general nature, the algorithms may be readily coded to meet the needs of many applications.