Ozone plays an important role in various water treatment schemes. However, it can be costly to produce. In many ozone generation systems, some 90 percent of the free oxygen (O2) used in the process is not converted to ozone (O3) and remains unused, at substantial cost.

Now The Linde Group has introduced the OZORA oxygen recovery system, designed to separate ozone from the oxygen stream and recycle the unused oxygen back to the ozone generator. This can reduce oxygen consumption significantly.

Developed from The Linde Group’s knowledge of adsorption processes, the system has been jointly tested and validated with SUEZ, a manufacturer of ozone generators and provider of water treatment equipment and services. OZORA systems can be sized to match new ozone generation units or engineered to retrofit existing systems. Peter Studer, program manager for the chemicals and environment industry at The Linde Group, talked about the technology in an interview with Treatment Plant Operator.

TPO: What was the basic process for developing this product and bringing it to market?

Studer: Years ago we noticed some interest in ozone in wastewater treatment, but our analysis found the ozone generators hadn’t reached the efficiency they needed to be cost-effective in that application. In the 1990s, as the drinking water market started to use ozone increasingly, especially in California, Florida, and dry-weather states like Texas, we noticed ozone generators becoming more efficient. In the early 2000s, we decided to try to save those water plants on their oxygen spend, and so we began developing our OZORA product.

TPO: Is pure oxygen typically the feed stream for ozone generation?

Studer: Yes. In most cases it is more efficient for ozone generators to run off of pure oxygen. Air contains only about 20 percent oxygen, so you would require much more power to produce the same amount of ozone.

TPO: In simple terms, how does the oxygen recycling process work?

Studer: An ozone generator typically produces only about 10 percent ozone, and the rest of the oxygen exits the generator unreacted. We take that stream of oxygen and bring it into the OZORA unit’s adsorbent beds where the ozone is captured in the pores of the material, in a manner similar to a sponge. The oxygen passes through and is recycled back to the front end of the ozone generator. Then we switch to another bed containing ozone. That bed receives dry air that removes the ozone and conveys it to the specific process where it is being used.

TPO: What are the benefits of this technology to the user?

Studer: It reduces their cost of oxygen. They will use only about 40 percent of what they’re currently using. Under our lease model, we expect to save the water treatment company at least 20 percent on their oxygen expense for ozone generation. So, a medium-sized water treatment plant in the U.S. producing 3,000 pounds per day of ozone, spending $550,000 a year on oxygen, would save an estimated $110,000 per year.

TPO: What is the ozone produced being used for most typically?

Studer: For drinking water, it’s used initially in pre-filtration steps to extend the life of filters by breaking down particles. Then the ozone would be used as a post-filtration step for primary disinfection, after which a small amount of chlorine would be added to sustain residual disinfection throughout the distribution system.

TPO: Is there a sweet spot in terms of the size of ozone generators for which this technology can be deployed? 

Studer: This technology works best on ozone generators that produce 1,000 pounds or more of ozone per day. The higher the production rate and the higher the rate of oxygen recovery, the greater the savings are likely to be.

TPO: Can this system be used on any manufacturer’s ozone generator in that size category?

Studer: Yes. We can work with the engineering company to include the system in the design of a new facility. We can also retrofit to existing ozone generators, and initially that is where we’re most likely to focus for the drinking water market.

TPO: What is involved in a retrofit?

Studer: Essentially our skid-mounted unit would be tied into the existing oxygen header with an inlet and an outlet and with block valves there. Then we would have a block valve on the ozone header, which would have an inlet for the ozone with oxygen and an outlet for the ozone and air. The block valves are there so that if the OZORA unit were to need maintenance, those valves would be opened, and the ozone generator would operate as if the OZORA unit wasn’t even there.

TPO: What was done to prove out this technology?

Studer: We developed our most recent design in 2015 with SUEZ (formerly Ozonia) as a collaborator. We worked with them at their facility in New Jersey to validate performance. That went very well. Then we used a SUEZ Water facility as a full-scale test, tying it into one of three ozone generators there. We’re ready to move forward with our commercial large-scale unit.

TPO: How would you describe the interest in the marketplace for this technology?

Studer: Interest has been very strong. Water districts and engineering companies are interested in getting to know the technology. Our trial finished up at the end of May, and we began sending proposals out over the summer. We are building units and looking at where we can install them.