Natrona County Uses Ozone To Treat Drinking Water

Natrona County’s drinking water is taken from the North Platte River and is treated at the Central Wyoming Regional Water System (RWS) with the primary disinfectant being ozone. The facility produces up to 25 million gallons of water per day. RWS uses chloramines as their secondary disifectant to keep bacteria from growing in the delivery system, including the pipes in your house.

At the RWS plant, after raw water is drawn from a well field that’s under the influence of the river, water is filtered and then ozone is used as their primary disinfectant.

Ozone is used because it’s better at killing giardia and other protozoan parasites like cryptosporidium (crypto) than chlorine. Protozoan parasites have hard outside surfaces. When chlorine is used in the process it requires longer contact times to kill bacteria.

Both RWS’ water plants is located low in the valley by the river. Once water is processed, it’s pumped uphill to high capacity tanks for storage. RWS operates 22 tanks. The system of high capacity tanks sits above the populations they serve and employ gravity to provide water pressure.

RWS’ water plant uses closed-system computers to operate their plants. Operators are able to gather information in real time from water flow and chemical analysis sensors, and use the computers to operate valves, introduce chemicals and automatically fill tanks. Supervisory control and data acquisition (SCADA) systems are common in the industry. Because their SCADA systems are closed systems, there’s no remote access to them from the Internet and operators must be on site to manage the plant.

The cost of the RWS facility in the range of $40-$50 million not including tanks or the distribution system. Tanks start at more than $1 million. Add the cost of miles and miles of underground lines, lift pumps, taps and other plumbing to the cost of the water plant and the total cost is much higher.


Ambient Ozone Measurement for Ozone Water Treatment

The use of ozone water treatment systems requires the measurement of ambient ozone levels as a safety measure. OSHA sets a 40 our exposure limit to ozone in spaces where people are present of 0.10 or less. Emissions from the ozone system or the down stream processes can exceed the OSHA levels. If this occurs, the ozone system should be shut down and the source of the ozone isolated. Normally, an ozone system will be interlocked with the ambient ozone monitor.

There are basically two different types of ambient ozone monitors: electrochemical and UV. The electrochemical sensors are less expensive and if there is not source of interference for these units, they are a good choice. They can see interference, especially from other oxidants that might be present, for example chlorine or one of its variants.

UV sensors are very accurate for low level ozone measurement, but much more expensive than electrochemical sensors. UV monitors are essentially UV spectrophotometers operating at 254 nm where ozone absorbs UV. They can also be affected by interferences, especially by aromatic hydrocarbons that also absorb UV at the 254 nm region. So, if these organic compounds are present UV monitors may not be a good choice for the application.

Because ambient ozone monitors are used for measuring ppb levels of ozone, it is a very challenging applications. Sometimes it is difficult to find the interference or to determine if there is an interfering compound. So, it is important to test the sensors against a known zero gas and calibrated ozone containing gas.

In general, electrochemical sensors are widely deployed for a variety of industrial and municipal drinking water applications. If problems develop a UV monitor might be a good option for checking the environment if calibration of the electrochemical sensors does not indicate the nature of the high ozone readings.