Silt density index , filter

SDI the Silt Density Index, a measure of the rate at which the water blocks a 0.45 im filter. 

Silt is formed by suspended particulates of all types that accumulate on the membrane surface. Typical sources of silt are organic colloids, iron corrosion products, precipitated iron hydroxide, algae, and fine particulate matter. A good predictor of the likelihood of a particular feed water to produce fouling by silt is the silt density index (SDI) of the feed water. The SDI, an empirical measurement (ASTM Standard D-4189-82,1987), is the time required to filter a fixed volume of... 

Figure 10.1. Experimental procedure for the determination of the colloidal index (Cl). The Cl or the silt density index (SDI) test is used to predict and prevent particulate fouling on the membrane surface. It measures the time required to filter a fixed volume of water through a standard 0.45- xm pore-size microfiltration membrane with a pressure of 2.07 bar. The difference between the initial time and the time of a second measurement after normally 15 minutes (after silt was built up) represents the Cl or SDI value.

Silt density index (SDI) is a test that measures the potential of an influent water to foul an RO membrane with suspended solids and colloids. The test involves timing flow of the influent water through a 0.45-micron filter pad.5... 

Figure 3.7 Silt density index pads taken before and after a filter treating RO influent water.

The effectiveness of UF in particle/colloid filtration can be measured with an MF plugging test similar to the "silt density index" (see Chapter 4, Figure 4.10). Water is fed at 30 psig through a 47 mm diameter 0.22 m membrane filter... 

SILT DENSITY INDEX - A measure of the tendency of a water to foul a reverse osmosis membrane, based on time flow through a membrane filter at constant pressure. 

Silt Density Index (SDI) It is an empirical measurement ASTM Standard D-4189-82, 1987) used for measuring the colloidal fouling potential of RO/NF feed water. It is not a direct measure of the particle concentration, which is more properly measured by turbidity. The SDI value is based on the time required to filter a volume of feed water throu a 0.45 pm filter pad at a feed pressure of 2.1 bar g. The SDI value is calculated from the formula ... 

Silt density index (SDl) is a sensitive method for determining the ability of a filter to remove colloidal particles 14). SDl (in min ) is used extensively as a criterion in minimizing fouling of reverse osmosis membranes. The lower the SDl value, the cleaner is the stream. Manufacturers of reverse osmosis membranes recommend that the stream be prefiltered so that it has an SDl factor less than 3.0. Typically 1 pm absolnte 6) filters have an SDl of about 4-5. Manufacturers of hallow fiber membrane filters claim SDI s in the range of 1.75 to 2.25. SDl measurements of effluents from the nano alumina media range from 0.5-1.0. The SDl of 32% PAC media was measured and found to be about 1.0. Turbidity as well as SDl tests have confirmed that the extent of shedding of PAC particles into effluent streams is minimal. 

Ground (Well) Water. If the source is of low turbidity and silt density index (SDI), a 10-pm cartridge filter system should be sufficient. A pressure filter at moderate filtration rate [4 to 6 gpm/ft (10 to 15 m/h)] may be added if necessary to handle any solids loading. 

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