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Engineering R&D: In-line waste incineration

February 1, 2007
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It sounds like the alchemist’s dream of turning lead into gold: a clean-in-place sanitation system that never requires changing water. It’s not alchemy, however, but chemical engineering and the principle of photon initiated oxidation, PIOx for short.

Thomas L. Grisham, partner, Analytical Environmental Laboratories, Tyler, TX.




Tyler, TX-based Southwest Dairy began applying PIOx technology in 2000 at one of six facilities for dairy and other food products. Jim Pitner, Southwest’s vice president of manufacturing, has told industry audiences that the technology has cut wastewater surcharges $500,000 a year at one of his plants.

With PIOx, photons are generated by a low-level ultraviolet lamp, creating ozone that permeates an inner, porous-walled tube. On the outer side of the tube is swirling water loaded with organic waste and cleaning solvents in the CIP water. To supplement ozone from the UV lamp, ozone in a gaseous state often is added to the tube from a nearby generator in commercial applications. When the ozone contacts the swirling water in the outer chamber, bubbles measuring 2 microns are formed, each containing ozone. The huge volume of tiny bubbles attach to particles in the water across 74,000 sq. in. of surface area in a pipe measuring 6 in. in diameter and 30 in. in length. The result is rapid oxidation of organic matter in the water. Carbon dioxide from the incinerated matter is vented, and the water-with sodium chloride cleaning salts intact-feeds back into the CIP loop. Theoretically, the CIP stream never has to be replaced, though Southwest changes its water periodically.

The pipe containing the photon-initiated oxidation unit at Southwest Dairy’s yogurt plant is depicted. The unit, which oxidizes BOD and other particles in wash water, is part of secondary loop in the CIP system. Source: Dairy Foods.

Dissolved air flotation is the fundamental physics of PIOx: When pressure is released in a pressurized fluid, bubbles are formed, and those bubbles attach to particles. Thomas L. Grisham first encountered the core technology in the late 1970s. The enormous surface area created could be as effective in removing chemical oxygen demand (COD) from a waste stream as precious metal from slurry, he reasoned, and he began a development voyage that ultimately led to PIOx.

A 1967 chemical engineering graduate of Texas A&M, Grisham worked for several chemical companies before becoming a partner at Tyler, TX-based Analytical Environmental Laboratories (AEL). The regulations for recycling and hazardous waste handling he helped develop in Minnesota became the model for EPA standards and launched his involvement in environmental engineering. Under Grisham’s direction, PIOx has been applied in several industries, though the company is focusing its efforts in dairy.

FE: How long have you worked on using ozone for waste stream treatment?

Grisham: While I was with Mobley Environmental Services, I heard a group from the University of Utah’s mining and metallurgy department explain the basics of an air sparging process for use in removing precious metals from coal slurry. I licensed the technology and in 1993 formed a firm in Houston to develop the business. We had lots of successes and one failure. Some colleagues and I then formed Retch Industries Inc. We filed and received five patents, but the firm encountered legal problems and fell apart, and the patents proved worthless. For the last seven years, we’ve taken a trade-secret approach in licensing the technology to industry.

To continue developing the technology, I became a consultant in Rosewood Corp., which was owned by the Hunt family. We tried to form a joint venture with Cargill, with $4 million investment from each party and first-year revenues projected at $20 million, but it was too small for Cargill to consider.

The effects of dissolved air flotation to pressurize a fluid can be seen in a soft-drink bottle. When the cap is removed, pressure is released, bubbles are formed, and the bubbles attach to particles and float to the top. The process is used extensively to remove precious metals from slurry, and it also can be used to reduce BODs (biological/biochemical organic demand) and other CODs from water.

FE: How is ozone generated in the system?

Grisham: Since 1890, scientists have known that shortwave UV light generates ozone, and that’s what PIOx is. UV light below the visible level, at a 185-nanometer wavelength, is used to convert oxygen to ozone. The ozone passes through the pores in the pipe to contact the swirling water, creating huge numbers of bubbles as it attaches to the CODs and oxidizes them.

The lamp doesn’t generate enough ozone to treat 50 gallons of water a minute, so we supplement the supply with gaseous ozone from a corona discharge generator. Pressure inside the pipe is 1.5 to 2 psi, which results in tremendous suction from the Bernoulli effect through the pores and into the tube.

FE: How has the technology changed over the last seven years?

Grisham: The low wattage from the UV light limits us. We’ve probably used 10 or 12 different lights to increase wattage by a factor of about five in that time. Like a lot of things, more is better.

We’ve made tremendous strides in better controlling the size of the pores in the tub, improving the inlet/outlet design, and refining different aspects. More recently, we adapted PIOx to clean CIP fluids for dairy pasteurizers. I very much buy into the whole concept of continuous improvement. We keep adding to the efficiency and effectiveness of the system.

FE: Why are you focusing on dairy applications instead of broader uses?

Grisham: Six different companies that make milk-based products are using the technology. Some are part of very large companies with multiple plants, but we haven’t had a company adopt the technology corporate wide.

The FDA issued a letter of no objection after reviewing the technology. They became intrigued and think more people should be using it. They have invited us to make presentations to the dairy industry six times, at FDA’s expense. A plant receiving tankers of raw milk might change the CIP fluid after two or three cycles; with this system, a tank truck could be unloaded and cleaned every hour with the same water. The water would stay at a level that is sufficient to achieve the cleanliness needed. At the end of the day, the fluid would keep cycling until it is totally clean for the next day’s deliveries.

This technology could be applied in fresh-cut produce plants, meat processing and any other facility that has to reduce BOD loads, but we’re focusing on dairy. If I can’t succeed when the FDA is saying this is wonderful technology for dairy plants, why bust our butts to get it applied elsewhere?

FE: Could PIOx be used to purify process water?

Grisham: This only affects organic materials. If you run salt water through it, it wouldn’t have any effect. That limitation is also what makes it appropriate for CIP, since chloride cleaning solvents are not removed. We’ve talked to municipalities about using the technology for drinking water and sewage treatment, but the volumes are overwhelming: thousands, even tens of thousands of gallons a minute.

The first place we applied the technology was at Kelly Tire, where it’s used to remove resorcinol from the waste stream. It was used successfully for two years.

FE: What changes have dairies had to make in order to apply PIOx?

Grisham: This is a non-invasive procedure: they do everything the way they’ve always done it. There’s just a second loop in the CIP system.

We try to make the cost as reasonable as possible. We fabricate the porous tube and assemble the whole unit, with the lamp, power supply and other components made to our specifications. The plant provides the piping, electricity and valving. We also get a monthly fee to maintain the system.

We take the same approach as Henry Ford took to the Model A’s color: you can have any size tube you want, as long as it’s 30 inches long and handles 50 gallons a minute. If higher volumes need to be processed, more units are added.

FE: What’s the plant’s level of risk?

Grisham: In my experience with the technology, it has never failed. The problem is, from a commercial standpoint, it has never been successful.

It is sorely needed technology, but the obstinateness of people to change slows adoption. On the other hand, three companies have asked us to make presentations, based on a talk we gave to the International Dairy Foods Association 14 months ago. We’re still hopeful.

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