Scanning Electron Microscopic Study of the Attachment Sstes of Suspenied Particles on the Sand Surface in Rapid Filtration

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(1) The X-ray analysis has indicated that chemical elements in the sand surface were Si, O, Al, Ca, Mg, Fe and K, in which the predominant elements and compound were Si and O, and SiO2 respectively and each and every element was distributed uniformly over the sand surface.(2) The scanning electron microscopic observation has made clear that the sand surface was composed of several planes divided by edges. On these lanes, there were some kinds of uneven faces such as steps, hollows, cracks, upheavals and so on, which would play the important roles in catching the suspended particles in the water.(3) In the first process of particle deposition in the filter, the existence of deposited particles splashed over the sand surface was observed. After that, these particles continued to catch subsequent particles and grew up rapidly. The masses of the particles contacted with adjoining ones shortly. The surface of the deposits become smoother and smoother as the filtration time passed. These results have indicated that the elucidation of the attachment sites of particles on the sand grain would be important.(4) Filtration experiments have been made by the use of both Au coated and uncoated sands. The efficienies of the particle removal in the experiments with the coated sands were only 1.5-3.0 % higher than that with the uncoated sands. This demonstrates that the chemical effects in the removal of suspended particles would be minor.(5) The surfaces of the sands, which had been used in the upward flow filtration or in the downward flow filtration, were observed by the scanning electron microscope. Most of the deposited particles were caught directly on the uneven faces of the sand surface such as hollows or cracks, or hanging o. These results indicate that the particle removal would depend to a great extent upon the physical effects.