Turbidity lime-soda

Chlorides. — Dissolve 5 gm. of soda-lime in 50 cc. of nitric acid, and dilute the solution with 100 cc. of water. The liquid should acquire at most a slight opalescent turbidity on the addition of silver nitrate solution. 

While the adjustment to the stability pH is often done with caustic soda, milk of lime is also suitable, providing its water insoluble content is sufficiently low (e.g., less than 2.0 %) to avoid causing an unacceptable increase in turbidity. 

One process sometimes used for low flow rates (<50 m /h) is lime or caustic soda softening followed by cross-flow microfiltration (XMF) and RO poHshing [21]. The MF membrane (pore size <0.2 pm) is tubular with a diameter of 1.27 or 2.54 cm. Due to the large diameter of the tubes, the membranes can handle feeds with sohd levels of up to 5% at a very high membrane flux (375—500 huh). The XMF filtrate is of high quality with turbidity <0.1 NTU and SDI < 3.0. 

For surface water, treatment is aimed primarily at removal of turbidity (fine suspended matter) and perhaps softening the water. The typical treatment processes for removal of turbidity involve the addition of chemicals such as alum or ferric chloride. The chemicals are rapidly mixed into the water so that they react with alkalinity in the water, then slowly mixed (flocculation) to form a settleable precipitate. After sedimentation, the water passes through a sand filter and finally is disinfected wdth chlorine. If the water is to be softened as part of the treatment, lime, Ca(OH)2, and soda ash, Na COj, are used in place of alum or ferric chloride, and the water hardness (calcium and magnesium ions) is removed along with its turbidity. 

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