Civil Eng Handbook - Chapter 10 - Chemical Water And Wastewater Treatment Prosesses.pdf

10
Chemical Water
and Wastewater
Treatment Processes
Coagulation
Colloids • Coagulation Chemistry
Softening, Stabilization, and Demineralization
Hardness • Lime/Soda Chemistry • Lead and Copper Control •
Ion Exchange • Sodium Cycle Softening • Chloride Cycle
Robert M. Sykes Dealkalization and Desulfurization • Demineralization
The Ohio State University Chemical Oxidation
Harold W. Walker Chemical Oxidants • Nondisinfection Uses Of Oxidants
The Ohio State University Disinfection
Waterborne Diseases • The Total Coliform Rule • Disinfectants •
Linda K. Weavers Disinfection ics • Contactor Design • Ultraviolet
The Ohio State University Irradiator Design • Disinfection By-Products
Coagulation
Surface waters contain a variety of suspended, colloidal solids that have aesthetic, economic, or health
impacts. Simple sedimentation and direct, unaided filtration are not practical in the case of clays and
organic detritus, because the overflow and filtration rates required for their removal lead to facilities that
are 100 to 200 times larger than those built today (Fanning, 1887; Fuller, 1898). Consequently, all surface
water treatment plants incorporate processes that destabilize and agglomerate colloids into larger, fast-
settling particles.
Colloids
Properties
Colloidal systems (dispersoids, colloidal dispersions, colloidal suspensions, colloidal solutions, and sols)
consist of particles suspended in some sort of medium. The position of the particles is
usually different from that of the medium, but examples where they are the same are known. Colloidal
systems are distinguished from true solutions and mechanical suspensions by the following criteria
(Voyutsky, 1978).
Opalescence
Colloidal systems scatter visible light. If a light beam is passed through a suspension of colloidal particles,
some of the light beam will be scattered at right angles, and a cloudy streak will be seen running al