Figure 1: O3 is used to purify water. Source: Kahn InstrumentsFigure 1: O3 is used to purify water. Source: Kahn InstrumentsOzone (O3) is increasingly used to purify water as an alternative to chlorination. There are four principle applications.

  • Production of potable water (i.e., drinking water)
  • Sterilization of feed water for food and pharmaceutical production
  • Sterilization of swimming pools
  • Sterilization of wastewater after treatment and before release into the water cycle

Historically, chlorination has been the preferred large-scale method of sterilization of water. However, there are significant health and safety risks involved in the bulk transport and application of chlorination systems. There are significant environmental implications through the release of chlorine into the water cycle. Also, chlorine can produce harmful, carcinogenic chlorohydrocarbons as a byproduct.

For these reasons, the implementation of ozone sterilizers has gathered pace in recent years. Both chlorination and ozonation have the same basic effect. Each are extremely powerful oxidizing agents, which attack the impurities – specifically, microbiological agents – in the water and break them down into harmless residues that can be filtered out of the water system. The advantage of ozone is that after it has reacted with the microbes it breaks down to oxygen, which is totally harmless.

Why is moisture critical?

Figure 2: Typical industrial ozone generation system. Source: Kahn InstrumentsFigure 2: Typical industrial ozone generation system. Source: Kahn Instruments

  • There are three main reasons to measure the moisture content of the feed air or oxygen in this process.
  • To prevent arcing in the generator electrodes
  • To prevent corrosion of system components due to nitric acid formation
  • To increase ozonation efficiency

A byproduct of arcing in the presence of ozone, nitrogen and water will be nitric acid and other nitrous compounds, which will cause corrosion of electrodes and system components, again leading to eventual failure of the ozone generator.

The efficiency of the ozone generator is inversely proportional to the moisture content of the feed gas. If the moisture content is reduced from 50 ppm to 5 ppm (from about -60° F to -100° F dew point), the generator efficiency can be increased by more than 20%.

A normal minimum specification for the air or nitrogen feed is -60° F dew point, but if this can be reduced by correct dryer control to -100° F dew point, the operating efficiency and lifetime of the plant can be improved significantly.

Measurement technique

Figure 3: Capacitive hygrometer. Source: Kahn InstrumentsFigure 3: Capacitive hygrometer. Source: Kahn Instruments

A capacitive hygrometer from Kahn Instruments can be used to monitor the moisture content of the feed gas either online (e.g., Easidew Transmitter, Easidew Online or Cermet II) or on a spot-check basis (e.g., Easidew Portable or HygroPort Portable Hygrometer).

In conjunction with a dryer control system, an online hygrometer can be used to ensure that the feed gas is as dry as possible, maintaining generator efficiency and lifetime.

For more information, visit Kahn Instruments’ hygrometer webpage.