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Ozone for Water Treatment

Ozone can be used for the treatment of water in multiple industries including municipal water treatment; wastewater; bottled water, wineries and breweries; aquaculture; drinking water for livestock; hydroponics; water treatment in cooling towers and air washers; public swimming pools; aquariums and zoos; commercial laundry facilities; soil/groundwater remediation and more.

Ozone is typically generated using the electrical discharge method where oxygen is exposed to high voltage resulting in oxygen molecules colliding with O2 to create the unstable O3 molecules.

Ozone is 13 times more soluble than oxygen. This solubility makes ozone very useful in many water treatment applications. Ozone can be dissolved in water much easier than oxygen although it does still require mechanical mixing.

Ozone is one of the most effective oxidants on earth, making it better than most chemical alternatives at breaking down contaminates and killing bacteria.

Ozone reacts differently in the air than it does in the water. While aqueous ozone (in water) does not create any hazardous effects, gaseous ozone (in the air) is hazardous to health.

Some of the Advantages:

  • Most effective disinfectant and oxidising agent available.
  • Not harmful to the environment.
  • Does not add chemicals to the water.

Some of the Disadvantages:

  • Instability – must be generated on site. Ozone storage is not possible.
  • Partially Soluble Gas – gaseous ozone can off-gas into the air from aqueous ozone.
  • Difficult to detect due to low vapour pressure (does not distribute evenly in the air).
  • Health hazardous of short-term exposure.

Ozone has many advantages in water treatment but one of the key disadvantages is the potential for occupational health issues resulting from worker exposure to off-gases of ozone in the workplace. It important for users of ozone to understand the hazards and understand how to effectively calibrate gas detection instruments used to measure ozone exposure.

Hazards:

640px-Ozone-CRC-MW-3D-ballsOzone Properties

Colour: pale blue or colourless

Odour: sweet and pungent, “electrical”

Solubility in Water: 0.640

Density: 2.144 g/l

Health Effects:

Ozone is both good and bad depending on where it is located in the atmosphere. In the upper atmosphere it works as a protective layer, filtering out harmful UV rays. In the ground level atmosphere, where we live, it can be extremely harmful to humans and plants.

Gaseous ozone can affect the respiratory, cardiovascular and central nervous system. These effects can take place within hours to a few days.

US health exposure limits (NIOSH):
PEL (Permissible) TWA 0.1 ppm (0.2 mg/m3)[1]
REL (Recommended) C 0.1 ppm (0.2 mg/m3)[1]
IDLH  (Immediate danger) 5 ppm[1]

Acute Exposure:

Exposure of 0.1 to 1 μmol/mol produces headaches, burning eyes and irritation to the respiratory passages. Although damage can be reversible, inhaled ozone gas harms the lungs and respiratory system by damaging the lung cells and causing a negative immune response. These immune responses can cause immediate inflammation, reduced protection and/or long-term increased risk of infection or exacerbating symptoms of asthma.

Ozone can also affect the heart by changing heart rate and/or cause veins to constrict which can lead to heart attack or stroke, particularly to those with previous heart conditions.

Chronic Exposure

Long-term exposure to ozone pollution has been found to be a contributing factor in lung disease. The risks of asthma symptoms and other respiratory diseases, and the potential for premature death, are greatly increased with chronic ozone exposure, ie: any exposure to ozone greater than 8 hours a day for a prolonged period of time (weeks – years).

Measurement and Calibration:

Portable and fixed systems to measure ozone are available using either electrochemical or semiconductor sensors. In either case, instruments must be calibrated (and routinely bump tested) to ensure accuracy and safety of the readings. Typically gas detection instruments use certified gas mixtures but calibration gas does not exist for ozone.

In recent years electronic calibration gas devices have been created for ozone providing certified gas concentration down to .2ppm.  These devices are portable, permitting their use for calibrating fixed systems as well as portable instruments.

ACD GENie 03 - OzoneThe genie O3 calibration gas  generator, sold by CAC GAS, provides customers with an easy and accurate way to calibrate gas detection instruments and/or fixed systems for ozone.

The compact, handheld design makes it portable and convenient for calibrating one device or multiple systems throughout a facility.

CAC GAS provides a variety of calibration and specialty gas solutions to the water treatment industry. For more information please see our Markets: Water & Wastewater Treatment page or contact us.

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