Process Description
The disinfecting method of chlorine dioxide is by oxidation (compared to chlorine which disinfects by means of chlorination). Chlorine dioxide, as a disinfectant, has many benefits over standard chlorine use:
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It will not form trihalomethanes when exposed to organics
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It is very effective over a wide pH range
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It reacts with sulfide compounds and eliminates odors (rotten egg smell)
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It disinfects 2 times faster than chlorine
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It can be removed by simple aeration or carbon dioxide addition
Chlorine dioxide is extremely volatile and cannot be manufactured and transported safely in compressed gas cylinders like chlorine gas. Therefore, a chlorine dioxide generator is used on-site to manufacture chlorine dioxide. Chlorine dioxide generators use sodium chlorite (NaClO2) as the feed chemical in manufacturing chlorine dioxide (sodium chlorate (NaClO3) can also be used). Chlorine dioxide is formed when sodium chlorite is introduced to either chlorine gas (Cl2), hypochlorous acid (HOCl), or hydrochloric acid (HCl). Temperature and pH are monitored during chlorine dioxide generation. The efficiency of chlorine dioxide to disinfect decreases (same as chlorine) as temperatures become lower. Chlorine dioxide should not be used as a disinfectant when the storage temperature of the sodium chlorite falls below 40°F (4°C); at this low temperature the sodium chlorite becomes separated into layers (stratification) and can damage the storage vessel. Monitoring pH may be required, depending on which chemical is used to generate the chlorine dioxide.
There are many uses for chlorine dioxide. It is used for disinfection in water treatment for municipalities, food, fruit and vegetable washing and beverage manufacturing. It is also used as a slimicide in paper and pulp machines and can be used in circuit board cleansing in the electronics industry. It is commonly used in wastewater treatment as well as industrial water treatment in applications such as cooling water utilities.
Measurements in chlorine dioxide:
Flow: Monitor the volume of liquid being treated with ClO2
pH: Monitor ClO2 injection from the chlorine dioxide generator.
Temperature: Monitor and control of temperature to ensure maximum disinfection.
Level using a pressure sensor : Monitor the hydrostatic level to accurately indicate chemical feed levels. |
