AMOEBIC DYSENTERY is an infectious intestinal disease. Symptoms are eruptions of the skin and frequent bowel movements. This disease is caused by a small animal instead of bacteria and resists ordinary chlorination. It is carried by amoebic cysts that foray in the intestines, then are discharged in the feces. Cysts (shell or sack) protect them and, when in water or moistened, they live for many days, but drying destroys them. The diatomite filter removes the cysts and super chlorination destroys them.
SCHISTOSOMIASIS is caused by a small worm that enters the body through consumption of contaminated water. Or, it may enter through the skin while a person is bathing or swimming in contaminated water. Eggs of this parasite (commonly called blood flukes) are discharged from an infected person through the urine or feces. In fresh water, these eggs hatch into very small, free-swimming larvae which are not infectious to humans. However, if these larvae can find freshwater snails to enter, they develop into the next form "cercariae," and become highly infectious to human beings. In water, larvae can live for only 24 hours and cercariae for only 36 hours. The effective remedy is to destroy all the snails at the water source. Once the snails are destroyed, the cycle is broken and the disease ceases.
DIARRHEA is a name given to several intestinal diseases characterized by cramps and frequent bowel movements with watery feces. Inadequate sanitary protection of food and water can cause diarrhea. When the disease is caused by food, it is restricted to those who consume the contaminated food; however, waterborne infection is likely to be widespread. Proper chlorination measures will eliminate waterborne diarrhea.
In addition to the specific waterborne diseases discussed above, there are several nonspecific disorders caused by impure water. One example is the staining or discoloring of teeth because of the presence of fluorides in drinking water.
Various methods of treatment and purification are used to eliminate impurities in water and make it pleasant to drink. You should be familiar with some of the principal methods commonly used, keeping in mind that safe, pure water is essential to naval operations everywhere. How well you carry out your duties in the treatment and purification of water concerns the health and welfare of all personnel using the water. Methods used in various combinations of field treatment and purification of water include coagulation, flocculation, sedimentation, filtration, and disinfection.
COAGULATION is a formation of gelatinous particles in water by chemical action. FLOCCULATION is the combination of these particles into a heavy precipitate (floc) that absorbs color and entangles bacteria and other suspended matter, as it settles. A common floc-forming chemical is aluminum sulfate (filter alum). When sufficient natural alkali is not present in the water to form a good floc, additional alkali (soda ash) must be added. Figure 7-3 shows how flocculation works. Mechanical devices, such as mixers, agitators, and baffles, are an advantage in flocculation because they keep the precipitate suspended in the water long enough to produce a heavy floc.
If you were to dip up a glassful of water from a moving stream and proceed promptly to observe its contents, you would probably discover a number of solid particles being held in suspension in the liquid. At first these particles are more or less equally dispersed; but as the water becomes still, they start settling to the bottom of the glass. The settling of solids in this manner is caused by the natural action of gravity. In the field of water treatment, clearing water
Figure 7-3. - The process of flocculation.Continue Reading