Progress 06/01/07 to 01/31/08
Outputs
OUTPUTS: The overall objective of this Phase I project was to verify in the laboratory that photoelectrocatalytic oxidation (PECO) could convert dissolved ammonia primarily into nitrogen gas at rates that were high enough for possible commercial applications in aquaculture. Numerous bench-scale tests in 250-mL batch reactors were performed to evaluate the effects of varying several reaction parameters on the rate of ammonia conversion and the distribution of products. Positive results from these tests resulted in the fabrication of several flow-through recirculating reactors. These model reactors are being evaluated for their performance in small-scale aquariums (up to 10 gallons in size). Initial results of this project were presented by Dr. Terence Barry at the Feb. 2008 meeting of the World Aquaculture Society (WAS) in Orlando, FL. These results were included in a provisional patent application that was submitted before the WAS meeting and will be described in more detail in an
upcoming publication. To date, AquaMost has generated considerable interest in the local investment community and has been requested to test its technology for an application involving the treatment of wastewater by a relatively small but well-established company working in this area. In addition, AquaMost has submitted a Phase II SBIR proposal that would extend this research to testing prototype devices with live fish.
PARTICIPANTS: Three co-founders of AquaMost played active roles in conducting the Phase I SBIR studies. Walter Zeltner, Ph.D., a physical chemist, served as the Principal Investigator. Terence Barry, Ph.D., an aquaculturist, advised on applications of the technology as it impacts fish and coordinated most day-to-day studies. Dean Tompkins, Ph.D., a mechanical engineer, oversaw device design and fabrication. The co-founders were assisted by two undergraduate students, Mr. Timothy Barry and Mr. Ramsey Kropp, who performed many of the tests and assays required for this project. Their input and suggestions proved quite helpful for the successful outcome of this project. The project included a subcontract with Prof. Marc Anderson at the University of Wisconsin - Madison that provided access to specialty electrochemical characterization instrumentation and technical assistance. In particular, one of Prof. Anderson's M.S. students, Mr. Greg Pepping, assisted on this project by performing
some parallel experiments using a different test system and by coordinating measurements of the concentrations of nitrite and nitrate ions produced during the reactions. Results of his studies are being prepared for publication.
TARGET AUDIENCES: The technology that was studied for this project involves the physical-chemical conversion of dissolved ammonia directly to nitrogen gas. Successful implementation of this technology would impact a variety of industries and individuals who use the products of those industries. Such industries include home aquariums, recirculation aquaculture, backyard ponds, public aquariums and zoos, zebrafish rearing systems for research, swimming pools and spas, wastewater treatment, and drinking water purification. If this technology can be applied to high concentrations of ammonia, it may also prove useful for a novel water desalination approach under investigation by other researchers.
Impacts
Four key variables were found to have the greatest effect on catalytic activity: the firing temperature of the photoanode, the applied voltage, light irradiance, and water salinity. Other variables tested including pH, initial ammonia concentration, and metallization of the anode had little or no effect on catalytic activity. When the key variables were optimized to provide the fastest ammonia removal rates, no nitrite was formed and less than 15% of the ammonia was converted to nitrate. Therefore, it appears that over 85% of the ammonia was oxidized directly to nitrogen gas. The catalytic activity was affected significantly by the temperature at which the photoanode was heated. This observation suggests that the crystalline structure of the active catalytic material has an important impact on its performance and indicates the importance of optimizing this parameter for whatever grade of titanium is employed for the electrode. As expected, ammonia removal was directly
proportional to applied voltage over a wide range of voltages. The rate of ammonia removal is much faster (6 to 10-fold faster) in seawater than in freshwater. Using a 9-watt flow-through prototype, we observed complete ammonia removal (initial conc. 0.6 mg/L) from 7 liters of seawater in 90 minutes. Less than 10% of this ammonia formed nitrate, and no nitrite was detected. The conclusion is that ~90% of the ammonia was converted into nitrogen gas. Further studies using live fish with flow-through reactors will be the focus of our Phase II investigations, although initial studies with fish have gone well and suggest that this technology can provide a viable replacement for biofilters. As expected, the studies performed during Phase I have indicated additional issues that must be addressed in commercializing this technology. Such issues include optimizing electrode geometry and sourcing a relatively inexpensive but effective grade of titanium. However, because results of these studies
have been quite positive overall, AquaMost continues to pursue commercialization of this technology.
Publications
- Barry, T., Zeltner, W., Tompkins, D., Kropp, R., Barry, T., Pepping, G., and Anderson, M. (2008). Photoelectrocatalytic device that removes ammonia from water. Aquaculture Engineering (in preparation).
- Pepping, G., Anderson, M., Barry, T. (2008) Photoelectrocatalytic oxidation of ammonia/ammonium using TiO2-coated Ti photoanode. Environmental Science and Technology (in preparation).
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