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Mixed Oxidants Frequently Asked

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					Mixed Oxidants: Frequently Asked Questions

What is the purpose of disinfectants in drinking water?
Disinfectants are used initially to inactivate or kill bacteria and microorganisms in the
raw water drawn from Lake Hartwell as part of the treatment process. In additon,
chlorine is added to the finished water prior to introducing it into the distribution system
to protect against recontamination that occurs in the distribution system through leaks and
other compromises. The U.S. Environmental Protection Agency (EPA) and the SC
Department of Health and Envornmental Control requires maintenance of at least 0.2
mg/L of chlorine residual leaving the treatment plant and at least a measurable trace
residual at all points in the distribution system.


My water is cloudy, is it still safe to drink?
Yes, all drinking water maintains a sufficient disinfectant residual to ensure public health.
Any cloudiness in the water is a result of mixed oxidants eliminating biofilms that may
be present in the existing water system. Biofilm is a thin film-like layer created by
bacteria that may develop in water distribution lines, cooling towers, and any other
aqueous environment. Biofilm is resistant to chlorine and is difficult to remove once it
starts. By eliminating any biofilm, mixed oxidants result in less bacterial contamination,
reduced disinfectant requirements, and more durable disinfectant residuals to prevent
recontamination. With less organics in distribution piping, fewer disinfection by-products
are formed.


Why change from something that has worked for over 40 years?
Since the Anderson Regional Joint Water System water treatment facilities are located on
Lake Hartwell near homes and and businesses, safety is an important consideration. On-
site generation of mixed oxidants eliminates the transportation, handling, and storage of
hazardous water disinfection chemicals like chlorine gas and concentrated bleach
(sodium hypochlorite). In addition to providing a safer environment, mixed oxidants
provide a water quality that is safer to drink. At the same doses and contact times as
conventional chlorine, mixed oxidants have been shown in numerous laboratory studies
to achieve a more thorough and more rapid inactivation of a wider range of microbes.
Finally, the on-site generation allows us to have better control on the cost of water
produced. Both chlorine gas and bulk hypochlorite have been increasing in cost over the
last several years, substantially more than the rate of increase of the cost of salt and
electricity, the key components of mixed oxidants.
Does this mean that the existing chlorine gas disinfection system was
bad or unhealthy?
No, quite the opposite, the U.S. Surgeon General has stated that disinfection of drinking
water primarily using chlorine gas has been the single biggest contributor to increased
longevity and public health in the United States over the past 100 years. While
potentially hazardous if released to the atmosphere; in minute quantities, chlorine gas is a
highly effective and safe disinfectant. Global circumstances and the risk of accidental
spill have led us to look for alternative methods of delivering the same benefits with less
overall risk.



What does on-site generation mean?
Typically, the resulting chlorine disinfectant is packaged in cylinders (chlorine gas) or
drums (sodium hypochlorite) and transported to the end user. In the 1970s, smaller
electrolytic equipment that uses common salt in order to move the process on site, and
eliminate the transportation and storage of hazardous chemicals became available. Over
the last several decades, both the on-site generation process and the equipment
availability have been refined and improved. Thus, only salt and electricity are delivered
to the plant. This eliminates the need to transport through the community and store
potentially hazardous chlorine gas at the plant-site.


How are mixed oxidants produced?
Mixed oxidants are generated using a process called electrolysis. In the process, an
electric current is passed through a salt brine solution. The resulting products are a
chlorine mixed oxidant solution and hydrogen gas. The hydrogen gas is vented and
disposed. The dilute chlorine-mixed oxidant solution (1% compared to 5% for household
bleach) is generated daily and stored at the plant for use through-out the day.




The electrolysis of salt to generate chlorine has been practiced for over a century. MIOX
technology capitalizes on the century-old practice of using salt electrolysis to generate
chlorine disinfectant.
What are mixed oxidants?
The mixed-oxidant solution is a mixture of chlorine and other chlor-oxygen compounds
that are generated electrolytically using salt, water, and power. Although the mixed-
oxidant solution is measured and dosed as free available chlorine (FAC), it acts like a
more active chlor-oxygen chemistry than traditional chlorine. In contrast to other chlorine
technologies, mixed oxidants offer a superior disinfection efficacy, elimination of
biofilm, a more durable chlorine residual, reduced formation of disinfection by-products
(DBPs), and improved taste and odor. Moreover, mixed oxidants readily oxidize
ammonia, sulfides, iron and manganese.



Will mixed oxidants affect the taste of the water?
Mixed oxidants break down odor causing compounds, such as phenols or
organochloramines. Mixed oxidants appear to remove the musty odors of geosmin and
methyl isoborneol (MIB) caused when the raw water source suffers algae blooms. Thus,
by neutralizing odor-causing compounds without adding a chemical taste mixed oxidants
result in significant reductions in taste and odor complaints.


Are mixed oxidants safe?
On-site generation of mixed oxidants uses only salt, water, and power as feedstocks.
Neither the salt nor the mixed oxidant produced is classified as hazardous by the
regulatory agencies. The concentration of the generated chlorine solution is below the
Hazardous Communications Standard (HCS) safety threshold limit of 1 percent.
Although hydrogen gas is evolved from the electrolytic process of on-site generation,
automatic venting designs or air dilution systems safely vent this gas to the atmosphere.
On-site generation has an excellent safety record, with more than 4,000 units, from a
variety of manufacturers, installed worldwide. There are no hazardous chemicals used,
transported, or stored with mixed oxidant on-site generation equipment.


Is the process expensive? Will my water bill go up?
The cost of operating an on-site generation system depends on the cost of salt and power.
In general, the lifecycle cost of on-site generation is very competitive with chlorine gas
alternatives, and is typically less than delivered hypochlorite and the advanced
disinfection technologies of chlorine dioxide, ozone and UV. In the case of the Anderson
Regional Joint Water System, our favorable cost of electricity has allowed us to generate
disinfectant on-site for less unit cost than purchasing it in bulk, either as gas or liquid
hypochlorite. With the the increasing cost trends in transporting chlorine gas, on-site
generation should produce significant cost savings over the life of the system.

				
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