Calcium Hypochlorite Tablet Chlorination

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application—chlorination

Calcium Hypochlorite Tablet Chlorination: Fact or Fiction? ablet chlorination, used as an alternative to the traditional T chlorination methods of gas and liquid, provides a unique combination that accurately and safely delivers chlorine to drinking water systems; however, there are many misconceptions that pervade

the potable water industry obscuring the facts. Using simple chemistry of chlorine have received increased interest because concerns over the formation of and engineering, it can be explained why and how tablet chlorination, disinfection byproducts (DBPs) have emerged; however, most of these alterna- along with the use of calcium hypochlorite tablets, can be a safe and tives (i.e., chloramine, chlorine dioxide and ozone) also produce DBPs. Less is cost-effective method for water treatment. known about the DBPs formed by some of the alternatives, and the risks using The Importance of Alternatives these technologies may be equivalent or In the drinking water industry, higher. Chlorine is still the most common chlorine gas and liquid bleach have drinking water disinfectant used today long been the standard chemical used and the one we have the most informa- in water chlorination and disinfection. tion about. On balance, the health risks The practice of using chlorine in drink- of not chlorinating water appear to be ing water treatment has been acclaimed greater than risks associated with DBPs. By Scott Betcher as one of the most significant public Emerging national security issues, health advances of the 20th century, if along with having to comply with other not the entire millennium. More than federal regulations such as EPA’s Risk 98% of water treatment plants use some Management Plan and OSHA’s Process form of chlorine to treat their water Safety Management, have pushed the because of several benefits: germicidal water and wastewater treatment industry Why tablet chlorination can be a potency, sustained residual disinfection to look for alternatives. Alternatives properties, taste and odor control, as like ozone, UV irradiation and chlorine safe & cost-effective alternative well as it being cost-efficient. In the past dioxide have been used. few years and more recently with the Although these other processes do to the traditional chlorination signing of the Bioterrorism Act by provide efficient disinfection capabilities, President Bush, the federal government each alternative has associated disadvan- methods of gas and liquid has increased the effort to keep this tages. Ozone and UV irradiation do not nation’s water supply safe. Disinfection provide a persistent residual disinfection of the public water supply should not capability and have relatively high oper- be compromised. ating and maintenance costs associated Water suppliers are continually being with them. Chlorine dioxide forms challenged to prevent the presence of organic byproducts and requires onsite disease-causing microorganisms in their generation equipment and the handling water systems and methods of treatment of several chemicals. vary depending on site-specific factors, as well as the quality of the raw water sup- Chlorine’s Benefits & ply. The importance of water disinfection Disadvantages is evidenced by the fact that most past As mentioned before, chlorine has cases of outbreaks of waterborne diseases many benefits. First, the use of chlorine were due to inadequate disinfection or no has been demonstrated to reduce the level disinfection at all. Alternatives to the use of microorganisms that cause waterborne

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application—chlorination

TABLE 2: Cost Entry FIGURE 1: 5-Year Cost Comparison Total Cost Total

An actual analysis utilizing this tool based on a 1-mgd plant requiring a 1-ppm residual. As demonstrated by this five-year, total cost comparison, calcium hypochlorite tablets in this case are economically competitive with the other products.

diseases. It is easy to apply, and small over time that can result in increased the bottom of the feeder so remaining the traditional chlorination methods amounts stay in the water from the treat- material costs to keep residual disinfec- tablets stay dry and do not dissolve pre- of gas and liquid. Tablet chlorination ment plant through the distribution sys- tion capability in the system. maturely. Calcium hypochlorite tablets systems accurately and safely deliver tem to the consumer’s tap. Chlorine also erode at a predictable rate that is depend- chlorine to drinking water systems. controls biological growth by eliminating The Alternative ent upon water flow to the unit; there- Upon considering alternative chlorina- bacteria, algae and other organisms. In looking for alternatives, one fore, highly accurate chlorine dosage can tion methods, thoroughly evaluate the Because chlorine oxidizes natural sub- needs not go far from the traditional be achieved by controlling the water flow cost of operation through economic stances such as decaying vegetation, reduc- forms of chlorine to find one. Water rate. The chlorinator effluent is then analysis tools. You may be surprised tion in odors and tastes can and do occur. treatment facilities have been turning returned to the main system flow provid- by the results. For these reasons, chlorine is still the pre- to another form of chlorine—calcium ing the desired level of available chlorine Calcium hypochlorite tablet erosion ferred solution of drinking water experts. hypochlorite—as their system for water to meet operational requirements. Tablet chlorinators and tablets meet federal Typically, two well-recognized forms of chlorination. Calcium hypochlorite chlorination systems can be fully auto- requirements including the NSF standards chlorine have been used in water treatment: dissociates in water and hypochlorous mated utilizing compound loop, residual 60 and 61 for drinking water, American the use of chlorine gas in cylinders and acid is formed. As with chlorine gas control or flow pace control, similar to Water Works Association B-300 and sodium hypochlorite (bleach) solutions. chemistry, hypochlorous acid is the chlorine gas or sodium hypochlorite sys- several USDA standards. Due to the physical nature of these chemi- disinfecting agent. tems. These systems have been used to The tablet chlorination systems are cals, both of these technologies present spe- Calcium hypochlorite is an attractive chlorinate water plants as large as 14-mgd currently being used for drinking water cific safety concerns about potential releases alternative to chlorine gas or sodium that have chlorine demands exceeding applications in over 40 states as the pri- and spills, and both typically require special hypochlorite (bleach) solutions because 400-lb per day. On the other end of the mary disinfection treatment or in remote buildings and spill containment designs. it is a dry form of chlorine that offers scale, smaller units have turndown ability booster chlorination stations. As regulato- These chemicals also present handling several handling advantages. Calcium to supply the 35-gpm well water user ry requirements and safety issues provide issues that need to be considered. For hypochlorite contains approximately without over-chlorination. The chlorina- more of an incentive for water treatment example, chlorine gas requires personnel 65% available chlorine, compared to tor has no moving parts, requires little plants to reconsider their water treatment training and use of personal protective the 12% in bleach, and does not require maintenance and provides long-term systems, it is important to recognize that equipment when changing cylinders. operator certification or containment reliability. The feeder with the designated calcium hypochlorite offers safety and low Similarly, handling drums of bleach is areas. Many facilities have opted for a 3-in. tablets provide the total solution maintenance benefits together with small difficult and presents safety issues. technology using calcium hypochlorite for water and wastewater treatment. capital investments. Calcium hypochlorite tablet systems as the preferred method technology is making the difference in TABLE 1: Alternatives of introducing chlorine disinfectant. Cost Comparison municipalities around the country. wqp This technology is selected because of On the surface it may seem calcium Chlorine gas: its lower capital costs, accuracy, reliabili- hypochlorite tablet systems cost more to About the Author Cl2 + H2O = HCl + HOCl ty, safe handling and maintenance bene- operate than other chlorine systems. For a Scott Betcher is market manager for Liquid Soda Bleach: fits. It has opened up new horizons in true cost evaluation, an economic analysis Calcium Hypochlorite, PPG Industries, Inc. NaOCl + H2O = NaOH + HOCl water chlorination for applications of should be conducted that considers the He can be reached at 724.325.5997, or by Calcium Hypochlorite (solid): many types and sizes. Calcium hypo- total cost of the system. The evaluation e-mail at [email protected]. Ca(OCl)2 + 2H2O = Ca(OH)2 + 2HOCl chlorite systems have been used for should consider capital costs as well as years and are currently being used for maintenance and operational costs. One (All three produce the same active sanitizer. HOCl disinfects, sanitizes and provides residual protection.) primary disinfection treatment or as a may be surprised by the results of the remote booster chlorination stations. economic analysis. Table 2 is an example LearnMore! For more information Maintenance costs are another factor. The Accu-Tab tablet chlorination of an economic analysis spreadsheet, related to this article, go to Keeping chlorine gas eductors and system from PPG Industries combines developed by PPG Industries. www.wqpmag.com/lm.cfm/wq070708 bleach addition pumps operating calcium hypochlorite in 3-in. tablet form efficiently is a chore because the equip- along with a specifically designed patent- Surprising Results 0For more information on this subject, ment’s small orifices are prone to clog- ed erosion feeder. Incoming water from a Calcium hypochlorite tablet chlorina- write in 1018 on the reader service card. ging. Bleach loses strength and efficacy side stream contacts only the tablets at tion has proved itself as an alternative to

26 WATER QUALITY PRODUCTS