Progress 08/15/18 to 04/14/19

Outputs
Target Audience:The primary audience for the proposed technology is the aquaculture industry but will also find interest from the general waste water industry including both municipal and industrial. Changes/Problems:We encountered two problems during the execution of our proposed research: deposition of the catalytic material onto carbon fiber and the analysis of nitrites in solution. The first issue was the inability to deposit the proposed catalytic materials onto carbon fiber at adequate loadings and with consistency. We examined deposition of each catalytic material under various conditions including applied voltage, deposition time, and with changes to bath chemistry. Additionally we examined the use of an oxidation process for the carbon fiber to provide an improved deposition surface. None of these changes were effective and the coverage of the catalysts were sparse and poorly adherent resulting in a change to a monel wire substrate material which performed well. This change was unexpected and allowed for little time to perform a complete analysis of the monel-based material. The second problem was in the analysis of nitrite species using Chemetrics vacu-vial test kits. We found the optical absorbance, used to determine the nitrite-nitrogen content, did not come to equilibrium for a long period of time (hours vs. the stated time of 10 minutes). We found that due to the high pH of our solution during treatment the test kit dye was not reacting as-intended. We adjusted the pH of our samples and eventually found this method to work adequately. This again was unexpected and its investigationresulted in lost time on the program. What opportunities for training and professional development has the project provided? Nothing Reported How have the results been disseminated to communities of interest? Nothing Reported What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? The traditional fishing industry has failed to meet thegrowing global demand for fish. In response, recirculating aquaculture systems (RAS) that reduce water consumption and intensify production is growing. By 2030 aquaculture is projected to meet 62% of the global fish demand, 40% of this production will be supplied by advanced recirculating systems.In the U.S., however, the import/export deficit in seafood continues to grow demonstrating the need for a competitive and sustainable aquaculture industry that can provide food security to the nation. A limiting factor impeding the expansion of aquaculture is the cost-effective removal of nitrogen from fish farm effluents and in recirculation systems. Fish productivity, health, and environmental concerns are all affected by the nitrogen content. Some forms of nitrogen are known to be toxic to fish and humans while other forms, although non-toxic, can affect the growth and behavior of fish. Skyhaven Systems, LLC investigated a novel water treatment system targeted for use in removing nitrogen species from recirculating aquaculture systems. The proposed system was electrochemically-based and utilized non-precious metal catalyst materials integrated into a radially flow reactor system. Bench-scale experiments demonstrated that the proposed catalytic materials were effective at removing nitrogenspecies. Performance of a scaled reactor design requires further optimizationto validate the commercial feasability of the system. Once successful, the proposed system would be advantageous foran RAS facility due toa reduction in water usage, simple operation, environmental friendliness, waste reduction, and a small mechanical profile. These characteristics would result in a lower operating cost and better control for economically producing healthy fish at large scalesmakingthe proposed technology attractive to both existing and new RAS facilities. Progress on the Phase I sub-objectives is described below: 1. Demonstrate deposition ofcatalyst on carbon fiber tow We examined the electrochemical deposition of both two different catalyst materials on carbon fiber tow. Our experiments found that these catalytic materials did not adhere well to the carbon fiber and thereby resulted in poor/scarce coverage of the carbon with the catalytic materials. Morphology and composition of the catalytic material also varied. For these reasons we decided to investigate deposition of the catalytic materials onto an alternate substrate material. We found that both catalysts adhered well to the new substrate and coverage of the catalyst along the wire was good. 1.a.Characterize the catalytic behavior of these materials relative to ammonia and nitrates Bench-scale testing showed good catalytic action for removal of both ammonia and nitrate/nitrite species under batch (non-flow) conditions. The conversion of ammonia to nitrates/nitrites appears to occur at a faster rate than the reduction of nitrates/nitrites to nitrogen gas. This led to the design of a two-stage filter system that could be further optimized for removal of each species. In the two-stage system ammoniaand nitrite content was reduced by approximately 44% and 12% respectively after 1 hour of operation (starting point of 21ppm NH3-N and 0.8 ppm NO2-N). 1.b.Verify composition and loading/distribution using SEM/EDS Scanning electron microscopy (SEM) verified the poor coverage of the catalyst materials onto carbon. Similarly it validated the improved coverage of the catalysts on monel wire. Energy dispersive spectroscopy (EDS) additionally indicated poor/random composition along the carbon fiber deposits. EDS could however not be utilized with the new substrate materialdue to the background interference of this material with the method. 2. Build a radial flow-thru reactor utilizing the above catalytic materials A process was successfully developed for building a radial flow reactor. The designincluded braided inner and outer electrodes, an electrical separator, a porous mandrel inlet, and a filter housing. Additionally a process for the in-situ electroplating of the electrodes was developed. 3.Test the radial flow-thru reactor for effectiveness of removing TAN (total ammonia nitrogen) Ammonia-nitrogen was reduced by up to 50% in a single electrochemical flow cell. Oxygenation of the input stream was shown to provide more effective removal of ammonia-nitrogen at the detriment of current efficiency. Nitrite-nitrogen content was also shown to be reduced by up to ~36% in the developed system. 4.Provide a preliminary unit cost for the proposed system The proposed system requires furtheroptimization that would potentially lead to significant differences in costing. Asystem level costing was therefore deemed pre-mature at this point in development. 5.Develop a scale-up plan for implementation in the Phase II effort It was determined that atwo-cell electrochemical system would be the most effective for the proposed denitrification process. Further optimization of these cells is required and will impact the scale-up for the proposed system.Beyond this,testing using an aquaculture simulant or actual waste water is needed to provide an adequate scale-up plan to account for peripheral components such as particulate filters, oxygenation, neutralization, and mixing. Based on these facts a specific plan was not developed and a Phase II effort was not proposed.

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