Why ppm, Not g/h? The Right Performance Indicator for Ozone Washing Systems
Introduction
The most common sales pitch when buying an ozone washing system is: “This generator produces X grams of ozone per hour.” It sounds impressive, but on its own this number tells you almost nothing. What actually determines the disinfection effect on the product surface or in the water is not the amount of ozone the generator produces (g/h), but the ozone concentration actually dissolved in the wash water (ppm or mg/L).
This post looks at why the gap between these two values is so significant, what question to ask during a purchase decision, and how the OCS-OZW series approaches this issue.
What Does g/h Tell You — and What Doesn't It?
g/h (grams per hour) is an input parameter describing the ozone generator's production capacity. It tells you how much ozone gas the generator can produce, but not how much of that gas is transferred into the water, how long it stays dissolved, or what concentration it actually reaches.
Two systems with the same g/h rating can deliver dramatically different real-world performance due to differences in injection method (the gap between a simple diffuser and a venturi + static mixer is large), tank volume, circulation flow rate, and water temperature. One system might produce 5 g/h and reach only 0.3 ppm in the water, while another with the same 5 g/h reaches 1.2 ppm thanks to better transfer efficiency — and the disinfection effect between the two differs substantially.
Why Is ppm the True Performance Indicator?
Dissolved ozone concentration (ppm) reflects the amount of ozone that the product or surface in contact with the water is actually exposed to. The CT value (concentration × contact time) commonly used in disinfection literature is based directly on this figure; it cannot be calculated from g/h.
Put another way: g/h is the size of the flame under the pot; ppm is how hot the water inside actually gets. The flame can be large, but if the pot is uncovered or it's windy, the water may never reach the desired temperature.
Variables That Create the Gap
The main factors determining the gap between g/h and ppm are: the gas-liquid contact method (a simple diffuser is low-efficiency, while venturi + static mixer or microbubble is high-efficiency), tank volume and circulation flow rate, water temperature (ozone decomposes faster in warm water), organic load in the water (dissolved ozone first reacts with organic matter before accumulating for disinfection), and feed gas type (oxygen-fed generators produce higher concentrations than air-fed ones).
If any of these variables is not optimised, even a generator with a high g/h rating can result in low ppm in the water — meaning the customer may have paid for a high-capacity generator without actually getting the performance they needed.
How Should It Be Measured?
Dissolved ozone can be continuously measured with an online dissolved ozone sensor, placed directly in the water and reporting real-time ppm values. Some systems offer a one-off lab measurement (e.g. iodometric titration), but continuous process monitoring requires an online sensor — since dissolved ozone can shift during the process as organic load changes or water temperature fluctuates.
The key question to ask during a purchase decision is: “How does this system show me the ppm it reaches in the water — not just how many g/h it produces?”
The OCS Ozone Approach
When designing the OCS-OZW series of fruit and vegetable washing systems, we put this principle at the centre: the key value the customer sees on the front panel is not generator capacity, but online-measured dissolved ozone (ppm). A venturi + static mixer combination (venturi + microbubble on the 250 PRO) delivers high transfer efficiency, and the PLC manages keeping the target ppm stable according to the product recipe.
If you would like to assess the actual ozone concentration your washing system achieves, get in touch for a free technical assessment.