Disinfection

Lyster Bag The lyster bag shown in figure 2-23 is primarily a dispensing unit for purified or distilled water. These bags are sturdy, watertight, and readily collapsible for packing. Water is withdrawn through small faucets at the bottom. When no other purification equipment is available, the lyster bag can be used to disinfect raw water. Chemical kits for purification are supplied with each lyster bag. When you must use a lyster bag for water treatment, follow the manufacturer’s instructions. Tank Trailers Tank trailers (fig. 2-24), like lyster bags, are designed as dispensing units for purified or distilled water; however, tank trailers may be used to disinfect raw water. The water is treated as directed by local medical authorities. The tank trailer, sometimes referred to as a “water buffalo,” has a capacity of 400 gallons of water. The unit comes equipped with faucets for dispensing the water. When desirable, water can be transferred from the tank trailer into a lyster bag. The responsibility for cleaning and disinfecting the tank trailer before it is filled with water belongs to the Utilitiesman. Figure 2-23.—Lyster bag. Figure 2-24.—Tank trailer. Disinfection Disinfection destroys harmful organisms (pathogenic viruses, bacteria, and protozoans) present in water by exposing them to specific concentrations of disinfecting agents or to heat. The Navy guidelines on disinfection are as follows. The superchlorination process is used to disinfect water containers (lyster bags, tank trailers, etc.) and distribution systems initially- before they are used or when they have become contaminated. Superchlorination is accomplished by chlorinating the water in a container or distribution system to at least 100 ppm FAC and holding it in the container for 4 hours. During the 4-hour period, the FAC must not drop below 50 ppm. If the ppm falls below 50 ppm the process must be repeated. A sign “POISON DO NOT DRINK” must be displayed clearly on all sides of the container or at all water outlets during this process. Using the three charts in table 2-2, choose the one that applies to the percentage of HTH material you intend to use. Let’s say the chief gave you a bottle of 65% granular calcium hypochlorite. You should use the chart that has the title “For 65% to 70% Granular Calcium Hypochlorite.” Now locate the amount of water you are going to treat. For our example here, let’s say that we are going to treat a 400-gallon tank trailer. Look on the correct chart and locate the quantity in gallons. There is no 400-gallon figure, so use the larger capacity of 500 gallons. Now follow over on the chart and locate the corresponding number of ounces to add to receive a 100 ppm FAC. The answer is 10 ounces. We have determined that 10 ounces of 65% calcium 2-28