Progress 09/01/02 to 08/31/06
Outputs
The core goal was the demonstration of the destruction of hazardous organic chemicals and microbes in water, at concentrations relevant to those encountered in the processing of fruits and vegetables, using ozone made from an oxygen-enriched air stream and a perfluoromembrane contactor. Additionally, a second goal was to demonstrate that the neither the targeted organic species nor their oxidized by-products transferred across the membrane into the gas stream. Both objectives were successfully met. The research described herein comprised three stages in a continuous operation. These were (1) the generation of ozone from an oxygen-enriched air stream that itself was prepared from the ambient atmosphere in the lab, (2) the passage of this ozone feed stream into a perfluoromembrane contactor, based on the monomers, perfluorodimethyldioxole and tetrafluoroethylene, and (3) the preferential, bubbleless transfer of the ozone across the membrane, such that oxidation of the
organic species in the water passing in a counter-flow mode was ensured. The quality of the treated water systems was assessed using UV-spectrophotometry and, when possible, gas chromatography. The quality of the gas exiting the contactor, i.e., with respect to whether or not it contained organic species, was assessed via gas chromatographic procedures. Critical results were obtained for water containing various levels of nitrobenzene. For each aqueous organic solution, UV-spectrophotometry revealed that oxidation of the targeted organic materials was successful. In most cases, the appearance of new absorption signals attributable to oxidized by-products accompanied the loss of the UV-absorption provided by the starting organic chemicals as the oxidation proceeded. These results show that the combined generation of ozone using oxygen-enriched air and the perfluoromembrane contactors constitute a viable technology to treat fruits and vegetables for the purposes of disinfection and
removal of unwanted organic chemicals. Critically, the potential for the transfer of organic species from the aqueous stream across the perfluoromembrane into the gas stream was not realized for all systems studied - nitrobenzene or its surrogates, toluene, and benzyl alcohol. In each case, neither the starting organic chemical nor its oxidized by-products transferred across the membrane in the gas stream.
Impacts
Technical improvements would make our system adaptable to current industrial technologies. An economic analysis finds that this approach is cost-competitive, especially in view of the fact that our product concept would not be degraded or consumed on use. The costs typically associated with consumable reagents, such as chlorination chemicals, are nonexistent with our approach. Additionally, our processing system is safer than the typical chlorination systems. Hazards presented to the public and workers during the transport and storage of chlorination disinfectants are absent in our system. The ozone that does not pass across the membrane exits and can be recycled in our system, a processing feature that is impossible with classical Mazzei-style injectors in which the gas and aqueous streams are co-mixed and unreacted ozone is lost as waste in the process scheme.
Publications
- No publications reported this period
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Progress 01/01/04 to 12/31/04
Outputs
During the last six month period we have completed the following: A. Confirmed that the existing CMS bubbleless ozone devices are simply not as cost effective as the Mazzei injector for delivery ozone. While their productivity is comparable, the fact matter is that the Mazzei injector in a relatively simple straight forward manner is able to get comparable level of bubbleless ozone into the water. Since the CMS membrane devices and their perfluoro flatsheet design are very expensive they appear to be non- competitive with the Mazzei system. B. We have prepared smaller size devices as originally targeted in the 1 to 0.3 to 1 square foot range. Unfortunately as discussed above these devices are not cost competitive. C. We have performed engineering simulations on the concept of using UV plus ozone for enhanced disinfection capability. These simulations indicate that the cost for supplying the disinfection will increase, this leads to an overall higher cost. Since the
existing product using just ozone is satisfactory we have an over design product for an application that is presently being satisfied with straight Mazzei based ozone. D. We have identified and done preliminary simulation work for developing low cost hollow fiber based bubbleless ozone systems. The advantages of these hollow fiber based systems are; dramatically reduced cost in combination with superior delivery of bubbleless ozone compared to the existing flatsheet design. Preliminary work on flatsheet (vs. hollow fiber) PVDF indicated excellent chemical compatibility with the CMS membranes and solvent system. In conjunction with the simulation we have identified an outside firm to collaborate with CMS to fabricate these hollow fiber PVDF membrane modules. The outside companies are presently supplying the PVDF hollow fibers in hydrophilic form. While this hydrophilic form is undesirable for our program, based on inputs from key consultants it appears that the cost to modify this
hydrophilic form to design hydrophobic form should be relatively straight forward. Specially, we believe that we simply need to remove the hydrophilic fillers from the PVDF formulation to get the desired hydrophobic PVDF hollow fibers. The plan is then to use these hydrophobic PVDF hollow fibers in our existing coating procedures to convert them to the non porous ozone resistant hollow fibers for supply bubblesless ozone. Therefore the following key tasks will be done over the next 12 months. A. Contract for the manufacture of hydrophobic PVDF B. Using CMS coating lines, convert to non-porous PVDF, hollow fibers with CMS coating (this coating line is presently being installed at CMS under a separate program and will not be expensed to USDA) C. Fabricate hollow fiber modules based on coated PVDF fabricated in B D. Demonstrate enhanced ozone delivery E. Provide key economics to demonstrate the cost effectiveness compared to Mazzei injector.
Impacts
In the first quarter of the year, we will be further examining this value proposition and reviewing the program for a possible expanded scope with the USDA.
Publications
- No publications reported this period
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Progress 10/01/03 to 12/31/03
Outputs
To date, Task 1 is completed. The remaining tasks have not been completed due to the completion of a long-term experiment to determine ozone concentrations in the off-gas when using an ozone sanitizer. An ozone sanitizing spray system was purchased from Pacific Ozone (Model M-18). The unit is able to deliver up to 100 gal/min water. The unit utilizes a venturi injector to introduce ozone into water up to a concentration of approximately 5 ppm. The system was modified to allow a membrane module (Pall Infuzor) to substitute the injection mechanism of the venturi injector. The unit was also equipped with measurement devices such as pressure, temperature, gaseous ozone concentration, and liquid ozone concentration monitors. The system came equipped with a destruct unit. The unit, when equipped with a membrane module, is able to deliver bubbleless ozone into water. To date, the mass transfer of oxygen of the Pall Infuzor has been extensively studied; however the collection
of mass transfer data of ozone has been limited. We expect greater ozone mass transfer than oxygen mass transfer through the membrane due to the O3/ O2 selectivity, but this must be verified. Also, neither water quality to determine the effects of ozonation nor disinfection studies have been performed. Extensive work to determine the amount of ozone off-gas generated by the spray system equipped with the membrane module has been completed over the past eight months. These experiments were important to determine the safety of the system for the end-user and determine if a competitive advantage existed against a venturi injector. The water from the unit previously described was sprayed into a confined space and the concentration of ozone in the off-gas was measured. These measurements showed that within seconds, the air was saturated with high ozone concentrations. From the off-gas experiments we have come to realize that we cannot introduce ozone into water for spray applications
significantly better than our competitor. We are examining other value propositions for the membrane modules, specifically the recycling of oxygen in ozonation processes. Oxygen makes up approximately 20% of ozonation costs. Our membrane modules have the unique property of isolating the gas stream from the liquid stream, which allows for any unused ozone and oxygen to be recycled without contamination.
Impacts
In the first quarter of the year, we will be further examining this value proposition and reviewing the program for a possible expanded scope with the USDA.
Publications
- No publications reported this period
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