抄録
In order to evaluate the fouling potential of feed water in the membrane separation processes, we proposed a modified Silt Density Index (MSDI) measured by using the membrane having a smaller pore size than 0.45 μm, of which pore size was commonly used. The modified SDI was calculated from the same equation to evaluate the standard SDI (SSDI) defined by ASTM. We derived the theoretical relationship between SDI (both of SSDI and MSDI) and the four kinds of plugging coefficient K for the models of complete blocking filtration, intermediate blocking filtration, standard blocking filtration and cake filtration, supposing that the filtration curve of filtration time vs. filtrate volume follows the specific filtration model, and the effectiveness of MSDI as a water quality index was examined through comparison with measured SDI using the membranes of 0.45 μm (SSDI) and 0.20 μm (MSDI). The following results were obtained; (1) In the range of small Kb (K of the complete blocking filtration model) ,the relationship between Kb and the calculated SDI was approximately represented by a single curve regardless of initial flux of membrane J0. As a result Ki (= Kb /J0, K of the intermediate blocking filtration model) which is used for the water quality index free from the liquid temperature could be estimated from the measured SDI if J0 was known. (2) The calculated SDI was influenced by an initial filtrate volume (for example, 500ml at SSDI measurement) except for the intermediate filtration model. However, it was shown that its effect was small within the practical range of K. (3) The difference between the measured SDI and the SDI calculated from K obtained from the actual filtration curve was small in the range of small value of K or testing time Tm, and gradually increased as these values became large due to the deviation of actual curve from the curve expected by the filtration model.
