Origin and Effects of Dissolved Solids

Filtration can remove fine suspended solids and microorganisms, and microfiltration membranes of cellulose acetate or polyamides are available that have pores 0.1-20 pm in diameter. Clogging of such fine Alters is an ever-present problem, and it is usual to pass the water through a coarser conventional Alter flrst. Ultraflltration with membranes having pores smaller than 0.1 pm requires application of pressures of a few bars to keep the membrane surface free of deposits, water flows parallel to the membrane surfaces, with only a small fraction passing through the membrane. The membranes typically consist of bundles of hollow cellulose acetate or polyamide fibers set in a plastic matrix. Ultrafiltration bears some resemblance to reverse osmosis technology, described in Section 14.4, with the major difference that reverse osmosis can remove dissolved matter, whereas ultrafiltration cannot. 

The most significant dissolved ionic solid in most natural freshwater is calcium carbonate (actually present mainly as the bicarbonate), and so, for the purpose of water treatment, it is convenient to express the concentration of any ionic solute as a CaCOs equivalent. The formula weight of the solute is divided by the valence and by the number of its cations—for CaCOs itself, this comes to 50.0—and the concentration (usually in mg kg , ppm) is converted to an equivalent concentration of CaCOs on this basis.  

The impact of water hardness due to calcium or magnesium ions on detergents was explained in Section 7.3.1 The source of most Ca + and Mg t- jji hard water is the dissolution of limestone (CaCOs) or dolomite [CaMg(COs)2]- Magnesium carbonate is fairly soluble (1.26 mmol at ambient temperature), but CaCOs is much less so (0.153 mmol L ). However, if the water contains dissolved CO2 (as indeed it will if it is exposed to the air see Exercise 14.9), the relatively freely soluble Ca(HCOs)2 forms, and the limestone slowly dissolves away  

Reaction 14.1 is reversible, however, and, if the solution is boiled, the CO2 is swept out in the steam, and CaCOs is reprecipitated until its own solubility is reached. Thus, part of the Ca -derived hardness is removed by boiling  

Boiling does not remove magnesium salts, nor CaCOs at its own solubility level, nor noncarbonate calcium (i.e., Ca + that is counterbalanced by Cl or another anion of which the Ca + salt is freely soluble). The hardness that remains after boiling is called permanent hardness. Permanent hardness plus temporary hardness is called the total hardness. 

---

Organic recovery eflBciency from aqueous solution by freeze concentration has been reported (4) to decrease as the specific conductance or total dissolved solids increased. A similar effect has been observed for the recovery of heavy metals from a variety of aqueous solutions. Figure 7 illustrates the recovery-suppressing effect of dissolved sohds on copper as measured by specific conductance in the range of 40 to 40,000 /Ltmhos/cm. The matrices include deionized-distilled water, 10 to 10" M phosphate buffers and tap waters originally at pH 4 0.5, and 0.12N (approximate) HCl solution at pH 1.4. The recovery of other heavy metal cations follows in a similar manner. 

Although it was not stated in the original article of Noyes and Whitney, it should be pointed out that the validity of the previous equation relies on the assumption that the amount used, qo, is greater than or equal to the amount required to saturate the dissolution medium, qs. Later on, (5.1) was modified [102,104] and expressed in terms of the dissolved amount of drug q(t) at time t while the effective surface area A of the solid was taken into account ... 

Wcistewater - Wastewater from the process can originate from blowdown of cooling tower water to control dissolved solids and from boiler blowdown and water treatment plants. In all cases the water will contain dissolved salts that have a low environmental effect. 

The most familiar is cavitation of ship propellers. At the periphery of the rotating propeller, the moving velocity is highest. Fluid dynamic effects cause the formation and collapse of gas bubbles near the tips. The collapse of the gas bubbles is so rapid that it causes violent pressure impulses that are audible. These pressure pulses shock the solid surfaces and cause localized pitting. The origin of the bubbles can be trapped air bubbles, dissolved air coming out of solution or water vapor. 

The solid HP As showed promising improvement in conductivity and fuel cell performance but dissolved in water formed by the electrochemical process of current generation [9]. This leaching of the acids led to decay in the performance of the fuel cells. To overcome the problem of electrolyte dissolutimi and the consequent short lifetime of the fuel cell, an approach was investigated in which the HPA was blocked inside a host material in such a way that it would maintain high proton conductivity of the original electrolyte. The immobilization of the HPA on a support could be attained by any of the three processes physisorption, chemical attachment, and entrapment. Since weak forces are involved in physisorption, it is not an effective method to avoid the solubilization and leaching of the HPA from the support. The processes of immobilization by chemical attachment or entrapment are more effective as they form covalent or ionic bonds with the host material and very stable materials can be prepared. 

---