ABSTRACT
Because of huge volume and flow conditions, the quality of natural water cannot be modified significantly within the body of water (Gupta, 1997). Consequently, the quality control approach is directed to the water withdrawn from a source for a specific use. The drawn water is treated prior to its use. Typically, the overall treatment of water (for potable use) consists of physical and chemical methods of treatment-unlike wastewater treatment where physical, chemical, and/or biological unit processes are used, depending on the desired quality of the effluent and operational limitations. The physical unit operations used in water treatment include
• Screening-This process removes large floating and suspended debris. • Mixing-Chemicals known as coagulants (e.g., alum) are mixed to make tiny particles
stick together. • Flocculation-Water mixed with coagulants is given a low motion to allow particles to
meet and floc together. • Sedimentation (settling)—Water is detained for a sufficient time so flocculated particles
settle by gravity. • Filtration-Fine particles still remaining in water after settling and some microorganisms
present are filtered through a bed of sand and coal.
