Ft amoft amo

= [(4,826,310+ 101,325) -101,325] - [262,900-0] = 4,563,410 N/m2

Therefore,

F = 77 76i46 6-i(4,563,410)1-057 = 0.20 -m— Ans 77.76(46.6) m2 • day

Effect of temperature on permeation rate. As shown in Equation (8.15), the flux is a function of the dynamic viscosity ft. Because ft is a function of temperature, the flux or permeation rate is therefore also a function of temperature. As temperature increases, the viscosity of water decreases. Thus, from the equation, the flux is expected to increase with increase in temperature. Correspondingly, it is also expected that the flux would decrease as the temperature decreases. Figure 8.6d shows the correction factor Cf for membrane surface area (for CA membranes) as a function of temperature relative to 25°C. As shown, lower temperatures have larger correction factors. This is due to the increase of f as the temperature decreases. The opposite is true for the higher temperatures. These correction factors are applied to the membrane surface area to produce the same flux relative to 25°C.

Percent solute rejection or removal. The other parameter important in the design and operation of RO units is the percent rejection or removal of solutes. Let Qo be the feed inflow, [Co] be the feed concentration of solutes, Qp be the permeate outflow, [Cp] be the permeate concentration of solutes, Qc be the concentrate outflow, and [Cc] be the concentrate concentration of solutes. By mass balance of solutes, the percent rejection R is

The index i refers to the solute species i.

Figure 8.6e shows the effect of operating time on percent rejection. As shown, this particular membrane rejects divalent ions better than it does the monovalent ions. Generally, percent rejection increases with the value of the ionic charge.

Example 8.4 A laboratory RO unit 152.4 cm in length and 30.48 cm in diameter has an active surface area of 102.18 m . It is used to treat a feedwater with the following composition: NaCl = 3,000 mg/L, CaCl2 = 300 mg/L, and MgSO4 =