Biological Agent Removal

The ROWPU also removes biological agents from a water source. Reverse osmosis removal characteristics for various chemical agents do not exist. Any biological agent that is not removed by the ROWPU will be eliminated by the chlorine residual maintained in the product water.

WATER TREATMENT EQUIPMENT

The Utilitiesman may be called upon to select and set up various types of field water treatment equipment. You must be familiar with the theory of operation, the capabilities, the installation considerations, and the maintenance requirements of this equipment. This section covers four types of water treatment equipment. They are distillation, reverse osmosis, filtration, and disinfection units.

DISTILLATION

In areas where a satisfactory freshwater source cannot be located and existing water treatment facilities are not usable, the distillation process can be used to obtain fresh drinking water from brackish water, seawater, or water containing excessive amounts of dissolved solids. Distillation is effective for removing radioactive contaminants from water. Since the output of distillation equipment is limited and the process is expensive, its use is restricted to situations in which no other process is adequate. Continuous flow or batch type of water purification equipment is used whenever possible.

Theory of Operation

Distillation consists of heating water to form steam, separating the steam from the remaining water, and then cooling the steam so it becomes water again (fig. 9-12). As the water is heated to form steam or water vapor and the vapor is separated and then cooled, solids dissolved in the water do not vaporize but remain behind in the raw water. A large amount of heat that is not evidenced as a rise in temperature is required to change (vaporize) boiling water into steam. The process whereby latent heat is removed and steam becomes water is called condensation.

Distillation in its simplest form

Figure 9-12. - Distillation in its simplest form.