Title: Water quality and its control
Description: In recent years hydraulic engineers have become more and more involved with environmental problems in lakes and reservoirs, rivers and coastal zones which are being polluted heavily by the increased human activities in private homes, urban life and industries. Physical as well as biochemical processes of pollution in such aquatic environments are described. Theories and means to predict the magnitude of environmental pollution and counter-measures are introduced.

A large amount of waste and sewage discharged into a lake or reservoir yields its eutrophication and causes phytoplankton bloom, i.e. the surface of the lake or reservoir is covered by a dirty green mat of phytoplankton. Water in such a lake has an odor unsuitable for drinking. Lakes and reservoirs in eutrophic states become anaerobic. This is fatal for fish life.

Rivers have naturally the ability of self-purification. However, over-loading of organic waste (sewage) into rivers is fatal, causing the decrease of dissolved oxygen due to the excessive oxygen consumption by bacteria and micro-organisms which are fed by organic waste. Optimal allocation methods of facilities for sewage treatment and water aeration are described, applying the methods used in control engineering.

A huge amount of waste heat which is used for a cooling system (condenser) is discharged from a thermal or nuclear electric power station into an ambient water body such as a river or a coastal water. The resulting increase in temperature of ambient water may have adverse effects on plant and animals (sea weed and fish or their larva) and destroy the ecosystem of the environment.

Methods of predicting the magnitude and spreading area of temperature rise due to waste heat and the effective countermeasures to reduce them are described.
Subjects: Water quality, Water, purification