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Electrocholorination

The Status of Chlorate Regulations & Impact on Water Treatment - MIOX

What is Chlorate?

Chlorate (ClO3-) is a highly oxidized form of chlorine. It can be introduced to a water source as an industrial or agricultural contaminate or into a finished water as a disinfection byproduct (DBP).

Chlorate Level Guidelines

  • Maximum Contaminant Level (MCL) is the maximum permissible level of a contaminant in water delivered to users of a public water system.
  • Health Advisories (HA) are non-enforceable and provide technical guidance to state agencies and other public health officials on health effects, analytical methodologies, and treatment technologies associated with drinking water contamination.
  • Health Reference Level (HRL) is a lifetime exposure concentration of a contaminant protective of adverse, non-cancer health effects, that assumes all the exposure to a contaminant is from drinking water.

Chlorate Regulation Challenges

Chlorate is not currently regulated in the United States and there is no enforceable Maximum Contaminant Limit (MCL). Chlorate is on the EPA’s Third Chemical Contaminant List (CCL3) and this indicates the intention of the Environmental Protection Agency (EPA) to review chlorate as a potential candidate for regulation under the Safe Drinking Water Act.

  • Canada MCL is 1,000 μg/L (1.0 mg/L)
  • WHO recommends a chlorate limit of 700 μg/L (0.7 mg/L)

While no final recommendation has been promulgated, literature on the topic indicated that the regulation may fall within the range of 210 μg/L (0.21 mg/L) to 700 μg/L (0.7 mg/L). While 210 μg/L (0.21 mg/L) is established by the EPA as a health reference level, it is conjectured that the EPA will not establish such a low level as it will seriously impact the viability of using delivered bulk hypochlorite in the marketplace. A level of 210 μg/L (0.21 mg/L) is also predicted to impact 34% of utilities using on-site generation.

Factors Influencing Chlorate Formation

The longer or higher of any of these, the more chlorate will form:

  • Storage time
  • Storage temperature
  • Hypochlorite concentration

To limit chlorate formation, users of bulk hypochlorite may need to:

  • Move storage indoors, if not already located there.
  • Cool the room where the hypochlorite is stored to slow degradation.
  • Require “born-on dating” from the manufacturers to ensure freshness.
  • Limit storage volumes.
  • Purchase lower concentrations to slow the degradation.
  • Dilute the concentrated hypochlorite once it has been delivered to the treatment plant.

All of these will have significant impact on cost!

What about On-Site Generated Sodium Hypochlorite?

On-site generation is when basic, simple chemicals are used to generate a chemical at the point of use. With the De Nora MIOX® on-site generator, the hypochlorite is generated using salt.

Chlorate Impacts On-Site Generation

Chlorate ions are produced as an undesirable side reaction of the electrochemical process. In the process, a portion of the hypochlorous acid or hypochlorite ions are oxidized at the anode to produce chlorate ions. Research to date on chlorate production by installed commercial electrolytic OSG systems has not found any correlation between OSG brand, age, capacity, or a variety of operational conditions.

Advantages of MIOX® On-Site Generation

  • Hypochlorite generated on-site is always fresh.
  • <1% chlorine concentration has a very slow degradation rate.
  • Modular in nature. As regulations change, upgrades are simple and easy to implement.
  • Safety due to limited hazardous chemical storage.
  • Operational costs are lower.
  • System is easy to operate and maintain.

How does MIOX® On-Site Generation work?

  • Softened water enters the electrolytic cell and brine tank. 
  • Salt and water mix in the brine tank to form saturated brine.
  • Saturated brine enters the electrolytic cell.
  • Electrical current is passed through the electrolytic cell producing oxidant.
  • Hydrogen gas produced during the electrolysis process is vented outside.
  • Oxidant solution leaves the electrolytic cell and is stored in the oxidant tank.
  • Oxidant solution is dosed into the treatment process by a metering pump.
  • OSG turns ON/OFF from a signal located inside the oxidant tank.

Source: Status of Chlorate Regulations & Impact at Water Treatment Plants, Randy Otts