While regulation is highly important, process control cannot be ignored. The next two points of interest are pre-UV destruct and on the loop return.

The pre-UV destruct sensor is often the sensor responsible for controlling the ozone generator. Through a PID loop, the ozone sensor will control system levels during normal operation and during sanitization. The shown placement of the sensor gives the best representation of the ozone level inside the storage tank. If this sensor were placed close to the ozone generator outlet, the ozone would not be well mixed and would not be representative of the levels inside the storage tank.

The loop return sensor is important during ozone sanitizations. During sanitization, the UV destruct will be turned off and the points of use closed. This allows the ozonated water to flow through the entire system. Ozone levels are typically increased during this time as well. Due to ozone’s short half-life, the loop return sensor is required to ensure proper sanitization levels at the end of the water loop. If the loop is long, ozone can degrade to the extent that sanitization levels are not met at the end of the loop, leaving a section of pipe un-sanitized. This sensor will monitor the water on the loop return to ensure this is not the case.

While three ozone sensors is the golden number, two sensors is also acceptable in an ozonated water system, providing all regulatory protection along with excellent process control. This comes with a caveat, though.

During normal operation, the two sensors will monitor pre-UV destruct and post-UV destruct. The pre-UV destruct sensor provides process control for the ozone generator, and the post-UV destruct sensor provides data showing that no ozone is breaking through the UV destruct.

During sanitization, the post-UV destruct sensor will monitor the loop return. No product is being made while sanitization is taking place and the points of use are closed, so the sensor that would normally monitor for ozone reaching points of use can move to the loop return and serve as the insurance that sanitization levels are met at the end of the loop.

This method is acceptable, and nothing is lost by setting up the ozone system this way. The only consideration is that the sensor must change which stream it is monitoring, either through an engineering control or by having personnel manually switch it. It should also be taken into account that the sensor should not have a long length of tubing between it and the measurement point since ozone’s half-life is so short.