Evaluate The Influence Of Operating Conditions And Water Composition On Silt Density Index And Modified Fouling Index

Reverse Osmosis is one of the main methods for the water purification anddesalination, has been widely used in desalination, sewage treatment, ultra pure waterproduce and other aspects. It has remarkable merits of low energy consumption, nopollution, strongly compatibility, convenient operation, low operating cost and so on.The pretreatment of RO feed water is very important, and the result of it has directrelationship with whether the RO system can operate normally and effectively. SiltDensity Index (SDI), which is widely used to evaluate the quality of RO feed water,can reflect the degree of the fouling of RO membrane comprehensively. However,SDI values were affected by many factors. Therefore research the influence ofoperating conditions on SDI can be better guidance to the RO pretreatment process.Modified Fouling Index (MFI) was theorized on the foundation of SDI, in addition toable to evaluate the RO feed water quality, but also to predict the time of ROmembrane flux decreased, so the MFI test method has a better application.This paper consider the influencing factors of SDI from operating conditions andwatery conditions, the result shown that the colloid iron and organic matter were themain factors that cause elevated the SDI value. For the water stream containingcolloidal iron and organic matters, the SDI value decreased with the decrease of thepH of the water stream, and increased dramatically with the increase of pH when thepH of the water stream is above7. When the temperature and pressure increased, theSDI values were shown a rising trend, but when the test interval and the measuredsamples increased, the SDI values were shown a downward trend. The difference ofthe test membrane lead to different results, the SDI value was smaller when chosen amembrane which resistance higher. However, the SDI values did not vary greatlywhen chosen different membrane. The orthogonal test was did and analyzed for thefour factors which are pH, colloids, organic matter, salt content, the results show thatin the stream which has colloids and organic matter, the main factor is pH, followedby colloidal, organic matter, salt content.This paper describes the principles and the methods of prediction of membranefouling of the MFI, research the impact of some factors on the MFI values. The resultsshowed that there was a linear relationship between the MFI and the particles content in the feed water. With the growth of operating time, the measured MFI valuesshowed a trend of decreases and then increases. When used different membrane in thetest, the measured MFI values varied. When the test pressure and temperaturechanged, the MFI values were basically unchanged with the pressure and temperaturecorrection.