25 May 2005
prevalently in the past (see paragraph 4-1.4.3 and Figure 4-11). Film fill has a higher
potential for fouling (plugging) due to adherence and entrapment of biomass and of SS
(i.e., dirt, silt, and sand). The cooling capacity of a cooling tower can be reduced if the
film fill is extensively fouled (see Figure 4-14). Instances of severe fouling have resulted
in the collapse of fill into the cooling tower basin. In addition, fouling deposits in the fill
can harbor pathogenic microbiological organisms such as Legionnaires' Disease.
Figure 4-14. Heavily Fouled Cooling Tower Film Fill
Legionella Bacteria. This type of bacteria is the cause of Legionnaires'
Disease. It can grow in cooling water systems even when a proper microbiological
control program has been maintained. This bacterium can be discharged in the drift
produced from all types of cooling tower systems. If a susceptible person inhales the
bacteria, the disease could possibly develop. Due to increased awareness by cooling
tower operators and the water treatment industry in general, the risk of being infected by
Legionella Pneumophila or other pathogenic microorganism from a cooling tower
system is probably not much greater today than it was a few years ago. Still, a number
of outbreaks of Legionnaires' Disease are reported each year throughout the country.
See paragraph 4-4.7 for more information on controlling Legionella.