Brackish conditions

Pyrite and Marcasite. High sulfide concentrations are found towards the central part of the study area, particularly where the overlying shales indicate brackish conditions existed on the southeastern side of the basin (Figure 2). This observation supports a similar finding by Guber ( ), rather than the conclusion of other workers that higher pyrite contents are associated with marine rocks ( ). 

The distributions of minerals within the Lower Kittanning seam can be related to depositional environment. Pyrite content is highest in areas which may have experienced brackish conditions. This distribution reflects the availability of iron and sulfur, and pH conditions within the swamp. Whereas much of the pyrite formed syngenetically, observations of sulfide modes of occurrence suggest that marcasite formed epigenetically. 

In the first half of the twentieth century the flora and fauna of the Aral Sea existed in quasistationary, brackish conditions [1-6]. The average salinity of waters of the high sea was 10-12 ppt. Insignificant fluctuations of level and salinity had a character of seasonal and interannual fluctuations. 

The clay mineral spectrum is characterized by the paragenesis of dioctahedral chlorites exhibiting primary crystallochemical features with dioctahedral illites sometimes containing swelling layers. This association is quite typical for continental deposits or those from brackish-water basins. In addition to chlorites with a stable structure we also observe swelling chlorites which are unstable on heat treatment and which occupy a sort of intermediate position between chlorite and vermiculite. It appears to represent a process of incomplete crystallization of minerals of the chlorite-vermiculite group in continental basins or under freshwater to brackish conditions. The minerals may thus be considered as metastable intermediate forms. 

Foraminifera are another group of rhizopod protozoans, but secrete calcareous, siliceous, or agglutinated tests. Foraminifera are marine, but tolerate a variety of brackish conditions as well as open ocean waters, and are both benthonic and planktonic in habitat. One specialized family, the Allogromiidae, lives in fresh water, but does not secrete a solid test. Foraminifera produce chambered tests in a wide variety of patterns (see Figure 8). Most foraminiferal tests... 

Aluminum has high resistance to atmospheric conditions as well as to industrial fumes and vapors and fresh, brackish, or salt waters. Many mineral acids attack aluminum, although the metal can be used with concentrated nitric acid (above 82 percent) and glacial acetic acid. Aluminum cannot be used with strong caustic solutions. 

These bacteria are anaerobic. They may survive but not actively grow when exposed to aerobic conditions. They occur in most natural waters including fresh, brackish, and sea water. Most soils and sediments contain sulfate reducers. Sulfate or sulfite must be present for active growth. The bacteria may tolerate temperatures as high as about 176°F (80°C) and a pH from about 5 to 9. 

For structures in brackish water, harbor water and fresh water, the conditions in each case should be considered and addressed on the basis of experience gained from other installations. Since harbor installations are usually very accessible, the cathodic protection installation can be extended if necessary. 

The main febricated parts of the units are carbon steel, with suitable corrosion allowance for the conditions of the chilled and condensing water. When brackish or sea water is used in a barometric condenser, steel construction with a V4 -in. to -in. corrosion allowance is suggested, and minimum wall plates of V2 -in. to -in. may be justified. Internal splash plates should be V2 -in. to -in. minimum, because the atmosphere of water vapor-air is very corrosive. Alloy construction is not justified except in exceptional cases. 

Platinised niobium and tantalum Niobium and tantalum can be used as substrate materials where environmental conditions dictate a higher driving voltage, e.g. brackish water. Use is limited due to relatively high cost. Copper cored materials are again available. 

With a growing scarcity of freshwater available for irrigation, other sources of lower quality like brackish water, saline water, and treated wastewater become more important as additional or substituting inputs for the agricultural sector. At the same time, it is clear that a sophisticated treatment like desalination or nanofiltration under current conditions is still far too expensive to be a major solution to future irrigation water needs. Hence adaptation of farming and irrigation practices to the particular water qualities constitutes a more viable approach. 

The reverse osmosis performance of the two membranes under typical brackish water conditions is shown in Figure 2 (I, reference membrane III, with bentonite). At a rejection of 85 % the flux is almost doubled (from 2000 to nearly 4000 l/m d), the effect becoming smaller when going to higher rejections. Maximum brackish water rejection of the bentonite membrane is 97 % as against 98 % for the reference membrane. 

Membrane Properties. The reverse osmosis performance of the bentonite-doped membrane under brackish water conditions is compared to that of the reference membrane in Figure 5 (I, reference membrane II, with organophilic bentonite). At low salt rejection the bentonite membrane again shows a higher initial flux than the reference membrane, the performance of the two becoming identical at the high rejection limit. 

The objective of employing organophilic bentonite is flux stabilization. In terms of the membrane compaction slope the stabilizing effect is exemplified by the following figures (brackish water conditions) reference, -0.10 bentonite-doped, -0.06. In a field test over 1300 hours on well water of 5200 ppm TDS at a pressure of 60 bar, starting with an initial flux of 1780 1/m d and 95 % rejection, a compaction slope of -0.058 was found under the same conditions the reference membrane had a compaction slope of -0.094. 

Test feeds include synthetic brackish water typical of southwest United States at approximately 3500 ppm, and a typical synthetic seawater at approximately 35,000 ppm. Test conditions include brackish water at 400 psig, 25°C and 760 psig, 25°C. Seawater testing is done at 1000 psig at 25°C and at 50 C. Chlorine sensitivity is evaluated through the use of a feed of brackish water, doped to include a nominal 100 ppm hypochlorite ion at pH 7.5 to 8.5. Chlorine concentration is monitored daily and adjusted to the nominal. 

Table I displays the results over several thousand hours of exemplary samples tested at zero length, zero recovery. Brackish water rejection under conditions specified are in excess of 99% at high pressure and greater than 98.5% at lower pressure such as 400 psi. Flux values displayed are those typical of early samples in the development of Quantro II. At low pressure against brackish water such values were 1-2 gfd. Recent values of samples tested under identical conditions have exhibited rejections of 94+% at a flux of 5-7 gfd at 400 psi.

In brackish waters, the same general corrosion principles may apply as for sea water. Experience has also shown that there may be considerable variation from plant to plant in the performance of metals, even where the cooling water comes out of the same general source such as a deep bay or estuary. There are coastal sites where the salinity may show very marked seasonal fluctuation. Protective film formation is essential for long lifetime in condenser tubing. Tubes installed at the season of the year when conditions are most favorable to form protective films tend to give longer service. 

Summing up the economics, one can say that brackish water of 2100 p.p.m. can be made into good water of 500 p.p.m. at a cost of about 18 cents per 1000 gallons, including salt disposal, with a possibility of producing it at about 14 cents. Similarly, sea water can be made usable at 72 cents per kilogallon, with an optimistic limit of 48 cents. The problem that remains, then, is how nearly can these optimum conditions be realized ... 

---