By G. Scott Fahey, P.E.
Summary: With so many methods to treat water, it was only a matter of time before those in the water transport industry would devise a way to treat water as it’s being delivered. In this case, water is carried by a tanker and treated with ozone. The 4-year-old system hopes to become a model used by future businesses.
On Oct. 2, 1996, the first load of spring water was transported from its mile-high Sierra Nevada source to a bottler in California’s Bay Area. As the truck pulled away the dream of owning and operating a business—specializing in the bulk wholesale of spring water—became reality. But now the hard part, will the business be successful?
The chances were good. Because the tanker fill-point location was an hour closer to the Bay Area than the next nearest competitor. Nonetheless, more customers were needed; or the dream of having one’s own business would shortly turn into a financial nightmare.
The pristine and undeveloped spring site had disadvantages too—no commercial power for miles. That fact became very problematic during the process of trying to obtain new customers, who considered ozone treatment of every load essential to greatly reduced bacterial contamination. But it became obvious that, to obtain additional customers, ozone treatment was a necessity.
The different options available for treating each load with ozone either prior to or while being filled were considered. But none seemed appropriate, because it would be too expensive to build a facility capable of treating the water with ozone in such a remote location, without the availability of commercial power. Therefore, it seemed the only way out of the dilemma was to treat each load with ozone in-transit on its way to market. Unfortunately, there wasn’t a system found that could treat water with ozone as a tanker is in-transit. Many in the water transport industry were skeptical and scoffed at a possible solution.
Many attempts failed before because standard ozone generation equipment is too delicate to withstand the vibration and jostling of a tanker-truck as it travels down the road. The Mac Co. suggested an air-cooled flat ceramic plate, di-electric ozone generator might be durable enough for the job. The rate of ozone production from that type of ozone generator is low, accounting for its infrequent use in water treatment applications. Still, taking advantage of the time available while the water was in-transit would lend itself to using the more durable di-electric generator.
Choosing the path
For this application, the most efficient method to achieve mass transfer of ozone into water is to uniformly mix small amounts of both with one another. Consequently, the idea of having a tube from an ozone generator bubbling ozone into a tanker was rejected. Using that method, the interface between the ozone and water would be too macroscopic to get the job done. So a Mazzei venturi injector, model No. 1583, was used to saturate the water with ozone. A pump would be needed to create a recirculation loop from the tanker through the venturi and back into the tanker. Based on the transport time to market, a treatment time limit of one hour was set. So theoretically, for all of a tanker’s 6,750 gallons to be treated in an hour, the pump would have to push 115 gallons per minute (gpm) through the venture.
In addition, the most effective method of producing ozone needed to be considered. The production rate is proportional to the electric current available, the positive pressure at the point of generation and the amount of oxygen available for conversion. An ozone generator was chosen for the task that produces 0.5 pounds of ozone per hour. It worked in combination with an oil-less compressor and air separator, which provide 90-to-95 percent pure oxygen to the ozone generator. The amount of electric power needed to drive the ozone generation equipment and a 115 gpm pump was 6 kilowatts per hour (Kw/h), which created a big problem.
Source of power
Initially, the system would be powered using the tanker-truck’s alternator. The DC power it produced would be converted to AC using an inverter, but the largest most reliable marine inverter found was only capable of handing 2.5 kW/h. The ozone generation equipment required 1.25 kW/h, leaving only enough power available to pump 30 gpm, using a pump rated at 85 percent efficiency. To reduce the amount of water needed to circulate past the venturi, a mixing eductor was installed inside the tank on the outlet end of the recirculation loop. The eductor draws in and mixes five gallons of water for every gallon pumped into it.
Essentially, the use of the eductor multiplies the treating efficiency of the system by a factor of six. The eductor was placed 13 feet from the rear of the tanker since it could influence water within that range. The recirculation loop’s inlet was located at the front of the tanker. Arranging the inlet and outlet in this manner created the greatest probability of the system treating all the water within the tanker and any surface the water contacts.
The next step was to isolate the ozone generation equipment from the road vibrations and jostling created by a tanker-truck in-transit. Initially the ozone generator and pump were mounted on and behind the tractor. An aluminum frame was built to support the compressor, air-separator, ozone generator and pump. The frame was then isolated from external jolts and jarring by supporting it on an air suspension system. The air suspension system created a separate frame of reference for the equipment as it moved down the road. The delicate electrical components of the equipment were also mounted with rubber vibration dampeners. With the pump connected to the two-inch diameter stainless steel recirculation loop with 1-½ inch Teflon tubing protected with stainless steel braid and swivel fittings, the system was completed.
In one hour the ozone level reached almost 0.2 ppm with the ozone generator set for maximum production. With that unit set at 80 percent production, 0.1 ppm was reached in one hour—the goal of the concept. The system works so well because of the water’s quality. The water is received from storage at a temperature of 46oF; for water, its pH value is very low, and it’s nearly bacteria-free—i.e., heterotrophic bacteria of less than 2 colony forming units per milliliter (cfu/ml). Thus, the rate at which the ozone decays is decreased, in turn leaving a high residual level in solution and benefiting the treatment process.
It’s been three years since the system’s inception. Since then, over 1,000 loads of the same spring water have been treated and delivered using the system. Jay Dee Transport, Beal Trailers and Mac Co. manufactured the initial unit, which proved to be so reliable that four additional units were built. To reduce the initial investment and cut costs of consumables like batteries, an oversized alternator, a power inverter and a dedicated truck tractor, the entire system is now mounted on the tanker where a diesel generator provides power. A control panel has been provided within the truck tractor cab, so the driver can monitor and operate the unit while in-transit. These improvements enable the tanker-confined system to operate independently of the tractor towing it. When a tractor needs maintenance, the control panel is easily moved to another tractor, so the treatment tanker can remain in operation.
The cost of the system is reasonable. Using a term of three years, an interest rate of nine percent and an amortization period of two to three loads per day, its capital cost is approximately one-tenth of a cent per gallon. That provides the comfort of knowing a tanker being filled with potable water is nearly bacteria free due to ozone treatment of the previous load. If a tanker hasn’t been in continuous use, it can be easily treated by filling it with potable water, turning on the unit and waiting until the desired ozone level is reached. A tanker can also be used as a source of ozonated water to pressure wash outside surfaces, after making minor changes to the recirculation loop.
The aquaculture industry may find the system useful too. With the ozone generator turned off, only pure oxygen is delivered to the recirculation loop, thereby keeping the water inside the tanker oxygenated as fish are transported to market. Once the fish are delivered, the tanker can be refilled with potable water. Then on the return trip home, the ozone unit can be turned on so the tanker can be treated with ozone. This will ensure the tanker is clean and ready to be refilled with fresh water for the next load, greatly reducing the chances of cross-contamination from one load to the next.
Based on the in-transit water treatment system’s commercial performance during the past three years, such a method looks to provide economic reliability and consistent results. The bulk sale and delivery of spring water has economically benefited from using the system; and its applications are as varied as the many different needs for having water oxygenated and/or treated with ozone.
About the author
G. Scott Fahey lives in Boise, Idaho, received his bachelor’s degree from the University of Idaho and is a registered professional civil engineer. He owns the Sugar Pine Spring Water™ Co., which for nearly five years has specialized in bulk wholesale and delivery of spring water to various water bottlers in central California and the San Francisco Bay Area. He developed and started using the system, O on the GO™, three years ago, and is being issued a U.S. Patent on the system. He can be reached at (208) 345-5170 or (208) 354-5107 (fax).