High molar mass polysaccharides (locust bean gum and karaya gum) and effluents from a mechanical pulp mill and a paper mill were nanofiltered with commercially available nanofiltration (NF) membranes. The effect of the filtration conditions on the flux (critical flux), retention, and the fouling of the membranes was studied. The experiments were conducted by increasing and decreasing the pressure and measuring the flux thus obtained.
The critical flux was observed to increase with increasing flow velocity and decreasing concentration. An increase in pH increased the electrostatic repulsion between the membrane and the dissociated (charged) components in the paper mill effluents. As a result, a higher critical flux was obtained and also the retentions of the charged substances improved. Only a weak form of the critical flux was observed with the mill effluents. The permeate flux deviated from the pure water flux even at the lowest pressure, but increased linearly with pressure until the weak form of the critical flux was exceeded. The small decrease in flux immediately after filtration was started was probably caused by the plugging of the free spaces in the membranes or by the adsorption of foulants onto the membrane surface.
In the filtrations with the high molar mass polysaccharides, a strong form of the critical flux as well as a weak form were observed. The significant irreversible fouling of the most hydrophobic membrane was due to adsorption of the model substances by hydrophobic interaction. A precleaning of the membranes with an alkaline cleaning agent improved the pure water fluxes by up to 30%, but it had only a small effect on the critical or the limiting flux. The pure water fluxes of precleaned membranes after filtration were still higher than the pure water fluxes of the untreated membranes before filtration. 相似文献
The third harmonic generation(THG) of a linear cavity Ti:sapphire regenerative amplifier by use of a K_3B_6O_(10)Cl(KBOC) crystal is studied for the first time. Output power up to 5.9 mW is obtained at a central wavelength of 263 nm,corresponding to a conversion efficiency of 4.5% to the second harmonic power. Our results show a tremendous potential for nonlinear frequency conversion into the deep ultraviolet range with the new crystal and the output laser power can be further improved. 相似文献
" Analysis is performed to study the slip effects on the peristaltic flow of non-Newtonian fluid in a curved channel with wall properties. The resulting nonlinear partial differential equations are transformed to a single ordinary differential equation in a stream function by using the assumptions of long wavelength and low Reynolds number. This differential equation is solved numerically by employing the built-in routine for solving nonlinear boundary value problems (BVPs) through the software Mathematica. In addition, the analytic solutions for small Deborah number are computed with a regular perturbation technique. It is noticed that the symmetry of bolus is destroyed in a curved channel. An intensification in the slip effect results in a larger magnitude of axial velocity. Further, the size and circulation of the trapped boluses increase with an increase in the slip parameter. Different from the case of planar channel, the axial velocity profiles are tilted towards the lower part of the channel. A comparative study between analytic and numerical solutions shows excellent agreement. 相似文献