Organics and Calcium

The clean membrane resistance Rm is calculated for pure water flux, while the fouling resistance Rf is the total resistance minus the membrane resistance (see equations (8.1) and (8.2)). AP is the 

The fouling resistance is high for the membranes with a high salt rejection (TFC-S, TFC-ULP) and low for the MF membranes. However, in MF, only a very small resistance is requited to cause considerable flux decline. The results show that the morphologies of the various fouling layers are very different. 

The cut-off, which was between 6 and 8 nm under unfouled conditions, has shifted to 20 nm under fouling conditions. The increase in rejection can be attributed to the larger solute size due to aggregation and pore adsorption which was demonstrated for UF in Chapter 6. This shows a clear increase in membrane rejection as fouling proceeds. 

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Both HA and FA were removed from solution in the presence of 25 mM calcium chloride at pH 10. At this pH, calcite precipitates and the interactions between organics and calcium are strongest. In the absence of calcium no precipitation occurred at pH 10. This may indicate the precipitation of a calcium-organic compound, co-precipation of organics with calcite or, simply adsorption of organics onto calcite surface sites. 

The aim of filtration experiments with organics and calcium present was to study two effects (i) the effect of organic size and type on rejection and fouling, and (ii) the effect of coagulation of the organics by calcium and subsequent surface or pore fouling. 

The objective here is to compare the rejection at these conditions (Table 7.19) to previous results at lower organic and calcium concentration (see Table 7.11, Table 7.13, Table 7.15, and Table 7.16 for TFC-SR, TFC-S, TFC-ULP, and CA-UF membranes, respectively). 

At pH 10 calcite precipitates and adsorbs a considerable amount of HA. This appeared in the solubility tests (see Chapter 4) as a coagulation process with observed floe formation. With the TFC-SR membrane this effect was not observed. Both organic and calcium deposition increase steadily with pH as shown in Figure 7.38 and Table 7.37. The low value for DOC on TFC-S at pH 7.5 is believed to be experimental error. 

Many stabilizers require costabilizers. Several organic costabilizers are quite useful with barium—zinc and calcium—zinc stabilizers, eg, P-diketones, epoxies, organophosphites, hindered phenols, and polyols (122). 

Salts of Organic Acids. Calcium salts of organic acids may be prepared by reaction of the carbonate hydroxide and the organic acid (9). Calcium lactate [814-80-2] is an iatermediate ia the purification of lactic acid from fermentation of molasses. Calcium soaps, soaps of fatty acids, ate soluble ia hydrocarbons, and are useful as waterproofing agents and constituents of greases (9). 

Calcium chloride is found in the marine environment. The elemental composition of seawater is 400 ppm calcium, 18,900 ppm chlorine, and many organisms and aquatic species are tolerant of these concentrations. Toxicity arises either from the invasion of freshwater in otherwise saltwater environments or possible toxic doses of calcium chloride from spills, surface mnoff, or underground percolation into typically freshwater streams or aquifers. Various agencies have guidelines for calcium and chloride in potable water (41). The European Economic Community (EEC) is the only agency to have a minimum specification for calcium in softened water. 

Resin cement materials are provided as a two-part powder—Hquid product. The powder consists largely of poly(methyl methacrylate) to which various fillers (qv) maybe added. These include calcium carbonate [471-34-1], siHca [7631-86-9], barium carbonate [513-77-9], and calcium tungstate [7790-75-2]. An organic peroxide, eg, benzoyl peroxide, capable of generating free radicals is also present (see Initiators Peroxides, organic). 

A base is any material that produces hydroxide ions when it is dissolved in water. The words alkaline, basic, and caustic are often used synonymously. Common bases include sodium hydroxide (lye), potassium hydroxide (potash lye), and calcium hydroxide (slaked lime). The concepts of strong versus weak bases, and concentrated versus dilute bases are exactly analogous to those for acids. Strong bases such as sodium hydroxide dissociate completely while weak bases such as the amines dissociate only partially. As with acids, bases can be either inorganic or organic. Typical reactions of bases include neutralization of acids, reaction with metals, and reaction with salts ... 

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