Ozone Sizing Guide – How Much Ozone Should You Use
Properly sizing an ozonation skid is a very important task when planning to use ozone for a particular application. Not adding enough ozone can undermine the effectiveness of the process while adding too much ozone can add unnecessary costs in terms of additional equipment needed to destroy ozone not consumed by the process.
Ozone Production Capacity Considerations:
Generally speaking there are four factors that determine how much ozone is required for a particular application:
Application: Different applications will require different concentrations of ozone. Even the same application will sometimes require a different concentration of ozone (i.e. wastewater treatment applications vary in their requirement for ozone depending on biological and chemical make-up of the effluent).
Contaminants: Ozone is a very strong oxidant, therefore ozone will react with both biological and non-biological contaminants and in general will be effective on both. The “one size fits all” approach cannot normally be used when sizing for anticipated ozone consumption during the particular process. Different elements react differently with ozone. Some applications need very small concentrations of ozone to oxidize contaminants while others will need much larger concentrations to complete the process. (i.e. certain biological organisms are harder to inactivate and therefore require higher ozone concentration).
Temperature and Pressure: Ozone is very effective at lower temperatures and less effective at higher temperatures. As such any application that requires higher temperatures to operate will be a less effective candidate for the use of ozone. Where the temperatures of the medium to be treated with ozone is above 40 degrees Celsius (104 Fahrenheit) the medium may need to be chilled in order to be more effectively treated by ozone.
While ozone works best at lower temperatures the extremely low temperatures are not desired either when considering using ozone.
Still, the optimum temperature for ozonation is strongly dependant on the type of contaminant present and there is no single number or range of temperature readings that produce the best result.
Alternatively, ozone will dissolve better in a pressurized medium therefore elevating the pressure of the application can also benefit the process.
Flow and Capacity: The amount of ozone required to effectively treat the contamination will depend on the flow rate and capacity of the application. The faster the flow rate (measured in gallons per minute GPM or liters per minute LPM) the shorter the contact time between the ozone and the liquid will be thereby resulting in a higher concentration of ozone required. Same can be said for capacity. 10, 000 gallons of effluent to be treated will require more ozone to be injected than treating 1,000 gallons of the same.
Ozone Dosing – General Guidelines:
The following are general guidelines published by “Water & Waste Digest” magazine (http://www.wwdmag.com/).
- Bottled Water: Low to Mid-Range Residual: (0.05 ppm -0.3 ppm)
- Cooling Tower: Low to Mid-Range Residual: (0.05 ppm -0.3 ppm)
- Water Reclamation: Mid to High Range: (0.2 ppm -0.5+ ppm)
- Iron, Sulfur and Manganese Oxidation: Ultra Low Range: (below detectable levels)
- Water Reclamation for Odor Control Only: Low Range: (Less than 0.01 ppm)
- Bacteria Kill: Mid to High Range: (0.2 ppm -0.5+ ppm)
Sizing an Ozone Generator – General Guidelines:
The following are general guidelines for sizing the ozone injection skid based on the type of application (source: http://www.wwdmag.com/)
- Iron, Sulfur, Manganese Oxidation: 0.5 grams/hour (500 ppm) per 5 GPM flow capacity.
- Bottled water to maintain purity: 1 gram/hour per 5 GPM flow capacity.
- Killing bacteria: (100 cfu) = 1 gram per 1 GPM flow capacity.
Other Considerations When Sizing an Ozone Injection Skid:
There are several other factors that could influence the size of the ozonation skid required.
Type of Injection: The larger the contact area ozone has with the contaminant the more effective it will be. Air stone diffusers typically generate large ozone bubbles therefore decreasing the overall contact area. The Venturi injector is a much better technology as it creates many micro bubbles therefore increasing the contact area of ozone with the contaminant. Having a larger contact area will result in a more effective utilization of ozone therefore requiring less ozone to be injected.
Inline Versus Mixing Tank Design:With an inline treatment the entire flow of liquid is treated with the ozone. This means that the ozonation skid will be required to process a larger flow volume. Larger flow volumes will require a larger processing capacity (larger pumps, injectors, etc.). A larger ozonation skid will also require more ozone since the utilization to loss ratio of ozone will also be higher.
The multi-stage mixing tank design typically involves diverting a smaller portion of the flow to the ozonation skid. Ozone is injected and dissolved at a higher than required concentration. The concentrated ozonated flow is then mixed with the main body of water diluting the ozone concentration to the required levels.
Monitoring the Dissolved Concentration of Ozone:
In order to be effective ozone must be kept in a desired concentration within the medium to be treated. A low dissolved concentration will undermine the effectiveness of the ozone and too high a concentration will cause ozone to escape unused therefore requiring larger ozone destruct unit.
So how do you ensure the ozone concentration is maintained at the proper level?
ORP (oxidation-reduction potential) or a REDOX probe will measure the concentration of the dissolved ozone by measuring the oxidation potential of the medium. Since ozone is a strong oxidant agent , the oxidation potential of the medium measured will rise as the concentration of ozone increases. If the concentration levels of ozone decrease the oxidation potential will decrease as well.
Positioning the ORP probe strategically within the application infrastructure will give relatively accurate readings of the ozone concentration at certain points of the system. For example, an ozone mixing tank (baffle tank) will require a higher concentration of ozone than the external storage tank. Placing an ORP probe within the baffle tank and the external tank will allow you to effectively measure and adjust the concentration at both points.
Ozone Sizing – Conclusion
Properly sizing the ozone injection and dissolve rates is an important step in engineering any ozone application. To properly size the amount of ozone needed for a particular application ( as well as to maintain the optimal dissolve rate of the ozone) an experience is the key factor. However in the majority of cases the complexity of factors present will make it very difficult to precisely determine the concentration and quantity of ozone required. In such cases a pre-deployment pilot study may be required. Gathering feedback about parameters and factors affecting the effectiveness of the ozone treatment will make the full implementation of the ozonation technology more effective as well as reduce the overall operating costs by sizing the ozone injection skid properly.
If you require additional help and assistance in sizing a unit, please contact an Ozmotics representative at 1-877-386-3763 for a complimentary consultation and review of your application’s requirements.
