Figure 5-5. 3,000-gallon fabric tank erected on ground platform made
of dimensioned lumber.
5-12. DIATOMITE FILTERS
Diatomite filters are included in several sets of Army equipment containing
pumps, tanks, and supplies that provide for pretreatment, chlorination, filtering, water
storage, and distribution. The diatomite filter unit is the most effective filtration system
ever devised by the Army and one of the most effective in existence. Diatomite, also
known as diatomaceous earth or filteraid, consists of the skeletal remains of minute
algae, called diatoms, found in marine deposits that have been lifted above sea level. It
is quarried and processed as filteraid, which is inert to water and water-treatment
chemicals.
5-13. CHLORINATION
Diatomite filtration of pretreated water removes over 90 percent of the bacteria,
all of the amoebic cysts, and all of the schistosome cercariae that may be present in the
water. However, the virus of infectious hepatitis is not removed or inactivated by this
treatment. Accordingly, the effluent from diatomite filters must be chlorinated to have a
minimum residual of 5 ppm after a 10-minute contact period. When the water
temperature is near freezing and the pH is near 7.0, a residual of not less than 10 ppm
is required. Chlorinated water must be allowed to stand an additional 20 minutes before
consumption. Higher residuals may be required when low temperature and high pH
conditions coexist in a water or when chlorine-demanding agents in the water
distribution system, introduced by subsequent rehandling, cause the residual to fall
below the standard chlorine residual (usually 5 ppm) after a 30-minute waiting period
subsequent to chlorination.
MD0008
5-14