Potable water disinfection process

As with any potable water treatment process, due consideration must be given to the reliability, economics, and competent operation of the disinfection process and related equipment, including ... 

An adequate supply of clean, potable WATER is one of the primary requirements for good health. Traditionally, health hazards associated with water have been the classic waterborne diseases, namely, typhoid, cholera, and hepatitis. The advent, advancement, and practice of the science of bacteriology after the late 18th century led to the recognition of the causes and sources of these diseases, which resulted in the development of disinfection processes and in the recognition of the necessity to prevent public potable water sources from pollution from sewage and postdisinfection contamination. 

Chlorine is used in a number of industrial processes, including the manufacture of plastics, solvents, and pesticides. Chlorine is also used as a bleach in the paper and textile industries and as a disinfectant in warer treatment. The use of chlorine to provide potable water has made life in large cities and our modern lifestyles feasible. 

Since the detection of halogenated organics in potable waters much research effort has been directed towards finding water treatment processes to remove such organics and their precursors and toward finding disinfectants other than chlorine. Great interest has been focused upon ozonisation because both disinfection and organic removal can be accomplished with this process. As ozonated end-products will occur in water produced by such processes and these could be potentially toxic and would accumulate in waste water after repeated cycles of use it is necessary to ascertain what end-products occur in water that has been ozonated and subsequently chlorinated. 

In addition to direct disinfection and sterilization, several surprisingly successful experiments about a decade ago led to the development of a number of highly proprietary processes in which ozone and other purifiers are introduced into chemical and wastewater flows in the presence of a cavitational field. The outcome has been greatly improved efficiency of the chemical action and the obtainment of purified or even potable water at economical costs. 

Momba, M. N. B., et al. (1998). Evaluation of the impact of disinfection processes on the formation of biofilms in potable surface water distribution systems. Water Science Technol. Wastewater Biological Processes, Proc. 199819th Biennial Conf. Int. Assoc, on Water Quality. Part 7, June 21-26,38, 8-9, 283-289. Elsevier Science Ltd., Exeter, England. 

Chloramination process can be applied to both water treatment and wastewater treatment (1,29). In the field of potable water treatment, chloramine is recommended as a secondary disinfectant because it is ineffective as a virucide, and is only marginally effective against Giardia cysts. It is formed from the combination of ammonia and chlorine (hypochlorite or hypochlorous acid). The chemical is generated on site, usually by injecting ammonia gas or adding an ammonium sulfate solution to chlorinated water. 

This chapter only discusses the applications of chlorination and chloramination in potable water treatment. In case the two processes are to be used for wastewater treatment, residual chlorine concentration in the plant effluent may become a regulatory issue (30). Selection of an alternative disinfectant becomes more important. New alternative disinfectants have been studied by Wang (19-25). Wang (35,36) also reported that UV is an effective process for dechlorination, dechloramination, or de-ozonation. 

Potable Water Chlorination and Chloramination chapter introduces the detailed engineering procedures for calculation of CT values for disinfection, and both conventional and innovative process equipment, including the on-site chlorine gas and hypochlorite generation facilities (2). 

The production of glyphosate herbicide (Round-up), the world s most successful herbicide, is another example of utilization of the catalytic properties of carbon surfaces [338], The Monsanto process by which Round-up is produced uses activated carbon as an oxidation catalyst for one of the key synthesis steps. The catalyst is produced by the treatment of activated carbon with ammonia at a high temperature to impart the desired nitrogen functionality. These functionalities are also commercially important for the reduction of chloramine in potable (drinking) water. Since water utilities are increasingly using chloramine rather than chlorine for water disinfection, and standard activated carbon products are not effective for removal of residual chloramine (which, for example, is highly toxic to dialysis patients), a catalytic carbon must be used to reduce its content [339,340],... 

Semi-dead end UF/MF membranes (effective pore size of the membrane is <0.1 pm) with intermittent backwash are being increasingly used for surface water and wastewater treatment for re-use, e.g. secondary or tertiary effluent is treated for industrial, non-potable and, in some cases, potable water reuse using UF/RO (or MF/RO) plus advanced oxidation techniques such as UV disinfection and hydrogen peroxide. The process is described in detail in Chapters 2 and 4 and several examples discussed in Chapter 3. Prominent examples of advanced reclamation plants include Water Factory 21 in Cahfornia, NEWater Factory in Singapore and the Goreangab Reclamation plant in Namibia [2]. 

To produce potable water which is safe to consume and free from turbidity, colour, odour and taste natural (raw) water abstracted from rivers, lakes, reservoirs and wells, etc., must be treated to remove pathogenic organisms, and mineral and organic contaminants. This is normally done by a process train comprising coagulation, flocculation, sedimentation and filtration followed by disinfection using either chlorine or ozone. 

The standard disinfectant for many of the world s potable drinking water supply systems (ozone and others are also widely used) and the product of choice for large cooling systems, usually available as a gas for lowest cost, but can be provided by liquids such as sodium hypochlorite (bleach) or solids such as calcium hypochlorite or isocyanurates. Any process contaminant leak tends to increase the chlorine demand, requiring additional chlorine to maintain disinfection rate. Poor penetrant of biomass and significantly reduced efficiencies over pH 8.0. 

Direct use of chlorine is in pulp and paper manufacturing and water treatment operations. Chlorine is used in the pulp and paper industiy to bleach the pulp to produce a high-quality whitened material, devoid of dark lignin and any other undesirable residuals. Chlorine has been the most common disinfectant and is still used by municipalities and others to treat potable, process, and waste water streams. Because of this specific use of chlorine, waterborne diseases such as typhoid and cholera have been eradicated in the industrialized world. Chlorine also removes hydrogen sulfide, iron compounds, and organic species that are responsible for objectionable tastes or odor associated with water. 

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