Analysis of the filtration curve and the effect of temperature on silt density index (SDI)

Abstract

Filtration curves of samples obtained at three different seawater pretreatment plants were analyzed in order to identify the blocking mechanism during silt density index (SDI) measurements of seawater and filtered seawater. This was done in two ways. Firstly, by direct comparison of the measured filtration curves with the calculated curves based on different constant-pressure dead-end filtration models, the coefficient of determination R2 was analyzed. Secondly, by changing the sample water temperature the measured SDI was compared to the calculated SDI in each model. The R2 of both standard blocking models and intermediate blocking models show higher values than those of the other models in the case of seawater filtration curves, indicating that these fit the measured filtration curves. The R2 of the cake filtration model is clearly smaller than those of other models. The measured SDI value of the same filtered seawater sample increases with temperature rise, this tendency coincides with the results calculated by all the filtration models. More precise analysis through R2 comparison of each model shows that the standard blocking model and the complete blocking model, which indicate relatively strong dependence of water temperature on SDI, best coincide with the measured results. The temperature dependency on SDI of the cake filtration model shows poor correlation with test results. Consequently, blocking coefficient (ks) of the standard blocking model is the most appropriate fouling indicator. The indicator ks can be the consistent fouling index, widely adaptable from seawater to filtered seawater after pretreatment. It is also noted that the standard blocking model can be applied for the quantitative evaluation of the effect of water temperature on SDI.