Progress 09/01/13 to 08/31/18
Outputs
Target Audience:Farmers: Local and business farmers, household gardeners who are interested in aquaculture/aquaponic systems/horticulture, and middle/high school students were the target audience. Researchers and Developers: We published four aquaponic papers to international journals, which are likely to reach a much broader audience. One Ph.D. student working on the project gave a poster presentation at the 30th Annual College of Tropical Agriculture and Human Resources (CTAHR) and College of Engineering (COE) Student Research Symposium, University of Hawaii at Manoa, April 6-7, 2018. The presentation was given to the students, researchers, and aquaponic growers in Hawaii. Undergraduate students: Four undergraduate students from Biological Engineering, University of Hawaii at Manoa involved in aquaponic related research. Other visitors: Groups of faculty, staffs, students, and local aquaponic growers in Hawaii visited the aquaponic research facility at University of Hawaii at Manoa. Changes/Problems:During 2017-2018, we finalized all of the project objectives. No problems were observed during the period. We focused on labeling stable nitrogen isotope study, adding 15NH4+ and 15NO3- to aquaponics as tracers. One challenge that we found was that nitrogen transformations had some links with other nutrients such as reactive phosphorus and dissolved carbon. To archive the overarching goal of nutrient recovery in aquaponic systems, all transformations of essential elements should be studied together. We will address this research need in the future study. Also, we suggested that developing aquaponic real-time and online water monitoring systems can help researcher and farmers to obtain the data for their efficient operations and development. What opportunities for training and professional development has the project provided?1. One Ph.D. student received training on the project. 2. During 2017-2018, four undergraduate students from Biological Engineering, University of Hawaii at Manoa, were mentored on this project, specifically on developing aquaponic technology for nutrient recovery. 3. During 2017-2018, the aquaponics facility and experiments were major showcases in the college for faculty, staffs, students, and local farmers in Hawaii. How have the results been disseminated to communities of interest?1. One review article, titled "Nitrogen transformations in aquaponic systems: A review," was listed as the most cited and most downloaded paper in Aquacultural Engineering Journal (Elsevier) (2018). 2. We submitted DNA sequences (16S rRNA genes) of the microbial community in aquaponic biofilters and plant roots to NCBI repository database. Researchers can access the DNA sequences using SRA accession number SRP150909 for further study. 3. One research paper, titled "Fate of nitrogen in a floating-raft aquaponic system using natural abundance nitrogen isotopic compositions," was published in the Journal of International Biodeterioration and Biodegradation in November 2017. 4. One research paper, titled "Influences of plant species and dissolved oxygen on nitrogen recovery and nitrous oxide (N2O) emissions from aquaponic systems" was published in the Journal of International Biodeterioration and Biodegradation in September 2018. 5. One research paper, titled "Aquaponic systems for sustainable resource recovery: Linking nitrogen transformations to microbial communities" was published in the Journal of Environmental Science and Technology in September 2018. 6. We collaborated with Mari's Gardens (a local aquaponic farm in Mililani, Hawaii) and Iliili Farm (a local aquaponic farm in Waianae, Hawaii) for monitoring water quality from aquaponic systems and developing monitoring systems and solids removal systems. During the collaboration, technology and knowledge were transferred and exchanged between the farms and our research team. The farms applied the knowledge from research while our research team learned other challenges in aquaponics from them. 7. The research results (poster presentation) were presented at the 30th Annual College of Tropical Agriculture and Human Resources (CTAHR) and College of Engineering (COE) Student Research Symposium, University of Hawaii at Manoa, April 6-7, 2018. The presentation was given to the students, researchers, and aquaponic growers in Hawaii. What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
Objective 1, "Quantify the impacts of physical and chemical variables that regulate nitrogen transformations in an aquaponic system." We grew four plant species, namely pak choi (Brassica rapa, sub. chinensis), romaine lettuce (Lactuca sativa var. longifolia), tomato (Solanum lycopersicum), and chive (Allium schoenoprasum). HLR, DO, pH, and feeding rate were the primary parameters that affected the nitrogen transformations. Based on the results, we recommend that pH should not be maintained below 6.0 in aquaponic systems. Aquaponic growers can reduce nitrogen loss by controlling sufficient DO in both biofilters and fish tanks together with balancing feeding rate to plants and fish. Strategies to archive the highest performance of aquaponics in term of nitrogen use are that the aquaponic growers should control a feed-to-plant ratio using nitrate as an indicator (no nitrate accumulation nor depletion is the optimumal condition) at neutral pH (6 - 7), maintain high DO (6 -7 mg/L in a fish tank) and use HLR of 1.5 m/day. These strategies will help aquaponic growers to improve NUE, increase overall productions, reduce the nitrogen loss, and maintain excellent water quality for fish and plants growth in aquaponic systems. Objective 2, "Monitor the transformations of different forms of nitrogen in aquaponic systems under optimized conditions." We found that nitrogen uptake rate by tomato was the highest followed by pak choi and lettuce. Chive had the lowest nitrogen recovery efficiency. The quantities of plant biomass and nitrogen in plants were directly related to nitrogen uptake rate by plants. We found five main outputs from aquaponic systems, namely plant biomass, fish biomass, nitrate nitrogen that accumulates in the recirculating water, sediments, and nitrogen loss. Nitrogen loss can be reduced by balancing the fish and the plant densities. There are four main dissolved nitrogen species in aquaponic recirculating water including dissolved organic nitrogen, TAN, nitrite, and nitrate. We found that nitrate was the indicator of the nitrogen availability for plants, which can be used to optimize feeding rate. To maintain sufficient nitrogen source for plants, increasing feeding rate is needed when nitrate depletion occurs or nitrate concentration is below 50 mgN/L. Based on the findings, we accomplished the goal of understanding nitrogen tranfomations for improving NUE in aquaponic systems. Objective 3, "Examine the ecology of functionally important microbes, and quantitatively assess their contributions during the redox cycling of nitrogen in an aquaponic system." Over the past years, we collaborated with Dr. Chandran's Lab at Columbia University for microbial community analyses in four aquaponic components including water in fish tank, biofilms, sediment in biofilters, and plant roots. The determinations of microbial structures and functions were based on two approaches namely qPCR and NGS. We found that nitrifying and non-nitrifying bacteria worked symbiotically. The groups of non-nitrifying bacteria were responsible for the degradation of organic compounds and contribution to nitrogen loss, where as the groups of nitrifying bacteria were responsible for nitrification. Interestingly, we found that plant roots served special roles that benefit nitrogen transformations. Plant roots likely protected the nitrifying bacteria when pH of recirculating water dropped to acidic levels (5.2-6.0). Nitrifying bacteria in plant roots, but not biofilters, survived at the acidic pH levels. Our findings also supported that nitrogen loss via denitrification was driven by the denitrifying bacteria, which were predominant over nitrifying bacteria in all aquaponic components. Also, with the isotope information (both natural abundance nitrogen isotopic compositions and labeling isotope studies), we confirmed that nitrate in aquaponic systems was the main nitrogen source taken up by plants before being assimilated into organic nitrogen in plant tissues. The outcomes of this objective provided the scientific information on nitrogen transformations in aquaponic systems that can explain how nitrogen transforms in aquaponic systems. Hence, aquaponic growers can use the comprehebsive information to develop efficient aquaponic systems. Objective 4, "Investigate the greenhouse gas emissions from aquaponic systems, with particular emphasis on nitrous oxide (N2O) emissions". We used gas chromatography - electron capture detector (GC-ECD) to investigate N2O emission from aquaponic and aquaculture (aquaponic with no plants) systems. N2O emissions from the two systems were not different. DO and plant species (chive, lettuce, tomato, and pak choi) affected the pathways of N2O emission but not the quantity of total N2O emission. We conducted two strategies to reduce the N2O emission using EMs and by aerating anoxic zone in biofilters. However, N2O emission was not reduced by those strategies because N2O emission released from aquaponic systems at both low and high DO concentrations in which denitrification and nitrifier-denitrification occurred simultaneously. EMs had a high abundance of heterotrophs, but organic carbon concentrations in aquaponic systems were not high enough to reduce the N2O emissions. Thus, denitrification and nitrous oxide emission were not reduced by adding EMs and aerating anoxic zone in biofilters. Interestingly, we found that increasing the number of plants or reducing the feeding rate effectively decreased N2O emission. Based on these findings, we suggested a strategy to improve NUE of aquaponic systems. The highest NUE was found at an optimum input (feed) in which input and products were in a balance. With the strategies, nitrogen loss and N2O emissions in aquaponic systems could be minimized, and the highest NUE could be archived. Overall, this study on the nitrogen transformations and microbial communities suggested that growing plants with high root surface area, providing high DO for plant roots, and balancing nitrogen input and outputs - all together- could enhance nitrification; thereby leading to the improvement in nutrient recovery in aquaponic systems. We published our findings in four different international journals, which could contribute to the science of aquaponics.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2018
Citation:
Wongkiew, S., Park, M.R., Chandran, K., and Khanal, S.K. (2018). Aquaponic systems for sustainable resource recovery: Linking nitrogen transformations to microbial communities. Environmental Science & Technology (in press). DOI: 10.1021/acs.est.8b04177
- Type:
Journal Articles
Status:
Published
Year Published:
2018
Citation:
Wongkiew, S., Popp, B.N., and Khanal, S.K. (2018). Nitrogen recovery and nitrous oxide (N2O) emissions from aquaponic systems: Influences of plant species and dissolved oxygen. International Biodeterioration & Biodegradation, 134, 117-126.
- Type:
Journal Articles
Status:
Published
Year Published:
2017
Citation:
Wongkiew, S., Popp, B.N., Kim, H.J., and Khanal, S.K. (2017). Fate of Nitrogen in Floating-Raft Aquaponic Systems using Natural Abundance Nitrogen Isotopic Compositions. International Biodeterioration & Biodegradation, 125, 24-32.
- Type:
Journal Articles
Status:
Published
Year Published:
2017
Citation:
Wongkiew, S., Hu, Z., Chandran, K., Lee, J.W., and Khanal, S.K. (2017). Nitrogen transformations in aquaponic systems: A review. Aquacultural Engineering, 76, 9-19.
- Type:
Theses/Dissertations
Status:
Published
Year Published:
2018
Citation:
NITROGEN CYCLE TRANSFORMATIONS IN FLOATING-RAFT AQUAPONIC SYSTEMS (2018). Ph.D. Dissertation. University of Hawaii at Manoa.
- Type:
Conference Papers and Presentations
Status:
Other
Year Published:
2018
Citation:
Wongkiew, S., and Khanal, S.K. (2018) A life story of nitrogen in aquaponics for resource recovery: Insights from molecular perspectives. Poster presentation. 30th Annual College of Tropical Agriculture and Human Resources (CTAHR) and College of Engineering (COE) Student Research Symposium, University of Hawaii at Manoa, April 6-7, 2018.
- Type:
Conference Papers and Presentations
Status:
Other
Year Published:
2017
Citation:
Wongkiew, S., Park, M.R., Popp, B.N., Chandran, K., and Khanal, S.K. (2017) Aquaponic System - An Emerging Technology for Resource Recovery. Oral presentation, The 2nd International Resource Recovery Conference, Columbia University, New York, August 5th-9th, 2017.
|
Progress 09/01/16 to 08/31/17
Outputs
Target Audience:Farmers: Local and business farmers, and household gardeners who are interested in aquaculture/aquaponic systems/horticulture, and middle/high school students are the target audience. Researchers and Developers: We published two papers entitled "Nitrogen transformations in aquaponic systems: A review in Aquacultural Engineering Journal, and "Fate of Nitrogen in Floating-Raft Aquaponic Systems using Natural Abundance Nitrogen Isotopic Compositions" in International Biodeterioration and Biodegradation Journal, which are likely to reach much broader audience. The first review paper became the most-downloaded paper in the journal One Ph.D. student working on the project gave an oral presentation at the 2nd International Resource Recovery Conference (IRRC 2017), Columbia University, New York, August 7-9th, 2017. The conference was given to the members of International Water Association (IWA) and registered attendees around the world. There were over 250 participants in the conference over 100 of them were in our presentation. Middle/high school students: One local middle school male students from Mid-Pacific Institute was involved in aquaponic related research, and one student from Well International School (Thailand) was also involved in aquaponic training during the project period. Other visitors: Groups of faculty, staffs, and students from Khon Kaen University (Thailand), Prince of Songkla Univerisity (Thailand), and Well International School (Thailand) also visited the aquaponic research facility at Magoon facility of University of Hawaii at Manoa. Changes/Problems:Methods and compounds used in isotope labeling study (objective 2) have been changed. We have spiked the solution of (15NH4)2(SO4) directly into the aquaponic water, not into the fish feed as proposed before. We made a change in this method because the variations in fish metabolisms and the aqueous distribution of fish feed mixed with (15NH4)2(SO4) could lead to a misinterpretations of downstream inorganic nitrogen transformations, which are the main process of nitrogen transformations in aquaponic systems. To solve this problem, we spiked the isotope solutions directly into the water. In addition, we have also spiked K15NO3- into our systems to evaluate denitrification and plant uptake of nitrate. The addition of K15NO3- was not previously described on the project narrative, but this addition of the isotope study will bring about a better and a deeper understanding of nitrogen transformations in aquaponic systems. What opportunities for training and professional development has the project provided?1. Two Ph.D., one undergraduate students and one post-doctoral trainee have been receiving training on the project. 2. The aquaponics facility has also been a major showcase in the college for faculty, staffs, and students from Khon Kaen University, Prince Songkla Univeristy, and Well international School, Thailand. 3. One high school student from Well International School (Thailand) was also mentored on this project, specifically on the operation and maintenance of aquaponic systems. 4. One middle school from Mid-Pacific Institute (Honolulu) was mentored in this project, specifically on nitritation (ammonia removal) from aquaponic effluent. How have the results been disseminated to communities of interest?1. One review articles, titled "Nitrogen transformations in aquaponic systems: A review", was published in Aquacultural Engineering Journal in 2017. The paper became the most downloaded paper in the journal. 2. One more research paper, titled "Fate of nitrogen in a floating-raft aquaponic system using natural abundance nitrogen isotopic compositions", was published in International Biodeterioration and Biodegradation Journal in 2017. One to two more research manuscripts have been prepared and expected to submit for further publications. 3. The research results (oral presentation) were presented at the 2nd International Resource Recovery Conference (IRRC 2017), Columbia University, New York, August 7-9th, 2017. The conference was given to the members of International Water Association (IWA) and registered attendees. There were almost 100 attendees in our presentation. 4. Aquaponic facility tour was organized for faculty, staffs, and students from Khon Kaen University, Prince Songkla Univeristy, and Well International School (Thailand). 5. We have collaborated with Mari's Gardens, a local aquaponic farm in Mililani, Hawai'i, for monitoring water quality from aquaponic systems. During the collaboration, technology and knowledge were transferred and exchanged between the farm and our research team. The farm applied the knowledge from research while our research team learnt other challenges in aquaponics from them. What do you plan to do during the next reporting period to accomplish the goals?We are now at the end of all experiments. There are few tasks to be completed, the last experiment on labeling isotope study and future publication on our results. We have applied labeling nitrogen isotope approach to complete the nitrogen cycle in aquaponic systems (objective 2). With the isotope study, the pathways of nitrogen transformations can be elucidated and concluded. We have been preparing a manuscript on microbial community in aquaponic systems for publication by the next reporting period. At the end of the next reporting period, the final report will be submitted, and the project will be completed.
Impacts
What was accomplished under these goals?
We completely accomplished the objective 1, "Quantify the impacts of physical and chemical variables that regulate nitrogen transformations in an aquaponic system", using the four plant species, namely pak choi (Brassica rapa, sub. chinensis), romaine lettuce (Lactuca sativa var. longifolia), tomato (Solanum lycopersicum), and chive (Allium schoenoprasum). HLR, DO, and pH were the primary parameters that affected the nitrogen transformations. HLRs of 0.25-2.5 m/d did not affect nitrogen transformations and nitrogen recovery performances in aquaponic systems. There was no significant difference on nitrogen transformations in this range. However, HLR below 0.25 m/d affected the nitrite oxidation, and this low HLR resulted in rapid increase in nitrite concentration. Moreover, HLR below 0.1 m/d affected the total ammonia nitrogen oxidation rate and therefore decreased the overall nitrification rate. Thus, the HLR in the range of 0.25-2.5 m/d maintained good water quality for fish and vegetable growth. In long-term operation, we expected that HLR below 0.25 m/d could cause fish illness and mortality due to the decrease in nitrite oxidation efficiency. However, HLR above 2.5 m/d is not recommended because of large energy requirement for recirculating water. Low pH (about 5-6) decreased TAN oxidation rate due to the inhibition of microorganisms responsible for nitrification. Based on the results, we recommend that pH should not be maintained below 6.0 in aquaponic system. We used natural abundance nitrogen isotope technique to investigate the effect of DO on nitrogen transformations. The occurrence of nitrogen loss via denitrification was confirmed by the nitrogen isotopic compositions (δ15N) in our study. The nitrogen loss was reduced by controlling sufficient DO in both biofilters and fish tanks, and balancing between feeding rate and nitrogen uptake rate by plants. Moreover, we found that controlling feed-to-plant ratio at neutral pH (6.8-7.2), high DO (6-7 mg/L in fish tank), and optimum HLR (1.5 m/d) were the best ways to increase NUE and reduce the nitrogen loss in aquaponic systems. We almost accomplished the objective 2, "Monitor the transformations of different forms of nitrogen in aquaponic systems under optimized conditions." We found that nitrogen uptake rate by tomato was the highest while nitrogen uptake rates by pak choi and lettuce were about the same. Chive assimilated the lowest amount of nitrogen. It was apparent that the amount of mass produced was directly related with nitrogen uptake by plants. We found five main different outputs from aquaponic systems, including plant biomass, fish biomass, nitrate nitrogen accumulated in the recirculating water, sediments, and nitrogen loss. Nitrogen loss can be reduced by balancing between input (fish feed) and the outputs. There are four main of dissolved nitrogen in aquaponic recirculating water including dissolved organic nitrogen, total ammonia nitrogen, nitrite, and nitrate. Total ammonia, nitrite and organic nitrogen concentrations did not increase over the time; however, nitrate concentration decreased or increased over the time, indicating the imbalance between input and outputs. Based on the findings, we can complete the nitrogen cycle in aquaponic systems and link the objective 1 to the objective 2 together. However, we have conducted labeling nitrogen isotope experiment to confirm the pathways and determine the rate of nitrogen transformations in the nitrogen cycle. We expect to finish this task, which is the last experiment, no later than the next year. We accomplished the objective 3, "Examine the ecology of functionally important microbes, and quantitatively assess their contributions during the redox cycling of nitrogen in an aquaponic system." Over the past years, we collaborated with Dr.Chandran's Lab at Columbia University for microbial community analyses in four aquaponic compartments including water in fish tank, biofilms, sediment in biofilters, and plant roots. The determinations of microbial structures and functions were based on two approaches including qPCR and high-throughput sequencing. We found that nitrifying and non-nitrifying bacteria lived together symbiotically. The groups of non-nitrifying bacteria were responsible for the degradation of organic compounds while the groups of nitrifying bacteria were responsible for inorganic nitrogen transformations. Interestingly, we found that plant roots served special functions that benefit nitrogen transformations. Plant roots can protect nitrifying bacteria when pH of recirculating water dropped to acidic levels. Nitrifying bacteria in plant root could work well under acidic pH levels, unlike nitrifying bacteria in other compartments of aquaponic systems. Our findings also supported that nitrogen loss via denitrification was driven by the non-nitrifying bacteria, called heterotrophs, which were predominant over nitrifying bacteria in all aquaponic compartments. Also, with the isotope information, we confirmed that nitrate in aquaponic systems was taken up by plants, and assimilated in to organic nitrogen in plant tissues. The outcomes of this objective provided the scientific information on nitrogen transformations in aquaponic systems and can support our finding very effectively. Hence, we can use the information to develop efficient aquaponic systems in the future. We have been preparing a manuscript about microbial community in aquaponic systems and expected to submit within this year. We accomplished the objective 4, "Investigate the greenhouse gas emissions from aquaponic systems, with particular emphasis on nitrous oxide (N2O) emissions". Over the past years, we used gas chromatography - electron capture detector (GC-ECD) to investigate N2O emission from aquaponic and aquaculture (aquaponic with no plants) systems. N2O emissions from two systems were not different. Plant species (chive, lettuce, tomato, and pak choi) did not affect the N2O emission. We conducted two strategies to reduce the N2O emission using effective microorganisms (EMs) and by aerating sediment zone in biofilters. However, N2O emission was not reduced by those strategies because high DO concentration inhibited the complete denitrification and hence increased the rate of N2O emissions. EMs consist of high abundance of heterotrophs, but organic carbon concentration in aquaponic systems was not high enough to activate them. Thus, denitrification and nitrous oxide emission were not reduced by EMs. Interestingly, we found that increasing the number of plants or reducing feeding rate effectively decreased N2O emission. Overall, we concluded that balancing between input (feed) and output (plants) will minimize N2O emission from aquaponic systems.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2017
Citation:
Wongkiew, S., Hu, Z., Chandran, K., Lee, J.W., and Khanal, S.K. 2017. Nitrogen transformations in aquaponic systems: A review. Aquacultural Engineering, 76, 9-19. (MOST-DOWNLOADED PAPER)
- Type:
Journal Articles
Status:
Awaiting Publication
Year Published:
2017
Citation:
Wongkiew, S., Popp, B.N., Kim, H.J., and Khanal, S.K. 2017. Fate of Nitrogen in Floating-Raft Aquaponic Systems using Natural Abundance Nitrogen Isotopic Compositions. International Biodeterioration & Biodegradation (in press).
- Type:
Conference Papers and Presentations
Status:
Other
Year Published:
2017
Citation:
Wongkiew, S., Park, M.R., Popp, B.N., Chandran, K., and Khanal, S.K. 2017. Aquaponic System - An Emerging Technology for Resource Recovery. Oral presentation. The 2nd International Resource Recovery Conference. Columbia University, New York. August 5-9, 2017.
|
Progress 09/01/15 to 08/31/16
Outputs
Target Audience:Researchers, local and business farmers, and household gardeners who are interested in aquaculture/aquaponic systems/horticulture, and middle/high school students are the target audience. We submitted one paper entitled "Nitrogen transformations in aquaponic systems: A review" for publication in Aquacultural Engineering, which is likely to reach much broader audience. One Ph.D. student working on the project gave a poster presentation at 28th Annual College of Tropical Agriculture and Human Resources (CTAHR) Student Research Symposium, University of Hawai'i at Manoa on April 8th, 2016. Two local high school female students from St. Andrew Priory School were involved in aquaponic related research and one biological engineering undergraduate student was also involved in aquaponic research during the project period. A group of students from Environmental Science Department, Nagasaki University (Japan) and staffs from Kapiolani Community College also visited the aquaponic research facility at Magoon facility of University of Hawaii at Manoa. Changes/Problems:Method for N2O investigation has been changed from probing method (indirect method) to gas chromatography - electron capture detector (GC-ECD) method due to better accuracy of GC-ECG and sampling method. The gas sampling method is now direct sampling, collected from the source of gas emission. What opportunities for training and professional development has the project provided?1. One Ph.D. student has been receiving training on the project. 2. Two high school students from St. Andrew's Priory School were mentored on some aspects of nitrogen transformations. 3. One undergraduate biological engineering student was mentored on aquaponic technology and food production. 4. The aquaponics facility has also been a major showcase in the college, welcoming students from Nagasaki University, Japan. 5. One high school student from Well International School (Thailand) was also mentored on operation aquaponic systems. How have the results been disseminated to communities of interest?1. One review article, titled Nitrogen transformations in aquaponic systems: A review, was submitted to Aquacultural Engineering Journal for publication. One more research paper, titled Nitrogen transformations in a floating-raft aquaponic system, has been finalized for submission. 2. Aquaponic facility tour was organized for students from Environmental Science Department, Nagasaki University (Japan) and staffs from Kapiolani Community College (Hawaii). 3. The research results were presented at 28th Annual CTAHR and COE Student Research Symposium, University of Hawaii at Manoa, April 8, 2016. The symposium was open to public. 4. Twenty invited lectures presented internationally in which various aspects of aquaponics project were covered. What do you plan to do during the next reporting period to accomplish the goals?In the next year plan, objective 3 on microbial analysis and objective 4 on N2O emission will be studied with all four plant species. We will then be able to correlate the nitrogen transformation results to microbial communities. As we found that nitrogen gas emission occurred in aquaponic systems (the objective 1), we do not know the ratio of nitrogen gas and nitrous oxide (N2O) gas. We are planning to investigate N2O emission, and reduce N2O emission by selecting the highest NUE plant. We will employ new method to analysis N2O using gas chromatography - electron capture detector (GC-ECD). The method is capable of direct gas sampling and multiple analyses of N2O gas samples. Moreover, the microbial sampling will be completed in the next few months. All of the samples will be shipped to our collaborator, Dr. Kartik Chandran' Lab in Colombia University for the microbial community analyses (qPCR and 16s rRNA). Two publications on the new findings of nitrogen transformations in aquaponic systems will be published. At the end of the project, we will apply labeling nitrogen isotope approach to complete the nitrogen cycle in aquaponic systems (objective 2). With the isotope study, the pathways of nitrogen transformations can be identified and concluded.
Impacts
What was accomplished under these goals?
Nitrogen is an essential element for fish and plant growth in aquaponic systems. However, nitrogen balance in aquaponic systems cannot be easily optimized because the rates of nitrogen transformations and the percentage contributions of nitrogen species depend on physical and chemical parameters such as hydraulic loading rate (HLR), dissolved oxygen (DO) and pH among others. We accomplished objective 1, "Quantify the impacts of physical and chemical variables that regulate nitrogen transformations in an aquaponic system", using the four plant species, namely pak choi (Brassica rapa, sub. chinensis), romaine lettuce (Lactuca sativa var. longifolia), tomato (Solanum lycopersicum) and chive (Allium schoenoprasum). Results showed that tomato assimilated the highest nitrate followed by pak choi and lettuce. Chive assimilated the lowest amount of nitrogen. It was apparent that the amount of mass produced was directly co-related with nitrogen uptake. Thus, in term of nitrogen utilization efficiency (NUE), tomato, pak choi and lettuce are recommended to grow effectively for recycling nitrogen waste from fish tanks. We also found that HLR, DO and pH were the primary parameters impacting the nitrogen transformations, but they regulated differently on the pathways of nitrogen oxidation and reduction. Aquaponic systems at HLR of 0.25-2.5 m/d did not show any impact on its performance. However, HLR below 0.25 m/d affected the nitrite oxidation, and this low HLR resulted in rapid increase in nitrite concentration. Moreover, HLR below 0.1 m/d affected the total ammonia nitrogen oxidation rate, and therefore decreased the overall nitrification rate. HLR between 0.25-2.5 m/d were studied, and we found that there was no significant difference on nitrogen transformations in this range. Thus, the HLR in the range of 0.25-2.5 m/d would maintain good water quality for fish and vegetable growth. In long-term operation, we expected that HLR below 0.25 m/d could cause fish illness and mortality due to reduced nitrite oxidation efficiency. However, HLR above 2.5 m/d is not recommended because of large energy requirement for recirculating water. Low pH (about 5.0) affected TAN oxidation rate due to inhibition of microorganisms responsible for nitrification. However, nitrification rate at pH of 6.0 was lower than that at pH 7.0. Based on the results, we recommend that pH should not be kept below 6.0 in aquaponic system. We used natural abundance nitrogen isotope technique to investigate the effect of DO on nitrogen transformations. The nitrogen loss via denitrification was confirmed by the nitrogen isotope ratio (δ15N) in our study. The nitrogen loss could be reduced by controlling sufficient DO in both biofilters and fish tanks. Moreover, we found that controlling feed-to-plant ratio at neutral pH, high DO and optimum HLR were the best ways to increase nitrogen utilization efficiency and reduce the nitrogen loss in aquaponic systems.
Publications
- Type:
Journal Articles
Status:
Submitted
Year Published:
2016
Citation:
Wongkiew, S., Hu, Z., Chandran, K., Lee, J.W., and Khanal, S.K. 2016. Nitrogen transformations in aquaponic systems: A review. Aquacultural Engineering.
- Type:
Journal Articles
Status:
Other
Year Published:
2016
Citation:
Wongkiew, S., Popp, B.N., and Khanal, S.K. 2016. Nitrogen transformations and denitrification in floating-raft aquaponic systems. Aquaculture (in-preparation for submission)
- Type:
Conference Papers and Presentations
Status:
Other
Year Published:
2016
Citation:
Wongkiew, S. and Khanal, S.K. 2016. Nitrogen transformations in floating-raft aquaponic systems, Poster Presentation. 28th Annual CTAHR and COE Student Research Symposium, University of Hawaii at Manoa, April 8, 2016.
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Progress 09/01/14 to 08/31/15
Outputs
Target Audience:During thereporting period,local farmersfrom farmer's market were given the tour of the aquaponics facility.The small business group from farmer's marketlearned the basics of soilless agriculture and the process. Graduate student working on the project gave an oral presentation at27th Annual College of Tropical Agriculture and Human Resources (CTAHR)Student Research Symposium, University of Hawai'i at Manoa on April 10, 2015. Two local highschool female students from St. Andrew Priory Schoolwere involved in aquaponics related research and one biological engineering undergraduate student was also involved in aquaponics research during the project period. A team of researchers from Tokyo University of Agriculture and Technology also visited the aquaponics research facility atMagoon facility of University of Hawaii at Manoa. Changes/Problems:One of the Co-PIs left the University during summer of 2014. The Co-PI was responsible for stable nitrogen isotope study. The PI has found a local researcher Prof. Brian Pop on the campus who is helping out to conduct the isotope study. What opportunities for training and professional development has the project provided?1. One Ph.D. student has been receiving trainingon the project. 2. Two high school students have beenmentored on some aspects of nitrogen transformations. Their project received 3rd place in International Science Fair, Pittsburg, PA in 2015. 3. One undergraduate biological engineering student has also been mentored on aquaponic technology. 4. The aquaponics facility has also been a major showcase in the college, welcoming researchers from Tokyo University of Agricultural and Technology and local vegetable vendors from farmers market. How have the results been disseminated to communities of interest?1. Aquaponic facility tour was organized forlocal vegetable vendors from farmers market. 2. The research results were presented at 27thAnnual CTAHR and COE Student Research Symposium, University of Hawaii at Manoa, April 11, 2015. The symposium was open to public. What do you plan to do during the next reporting period to accomplish the goals?The nitrogen transformations experiments (objectives 1 to 3)for Romaine lettuce, chive and tomato-based aquaponic systems will be studied in 2015 to 2016. Feeding rate will also be examined in order to reduce the denitrification rate and improve NUE. Microbial molecular analyses will be conducted toexaminethe biological side of nitrogen transformations. Two publications on nitrogen transformations in aquaponic systems will be published.
Impacts
What was accomplished under these goals?
Nitrogen is the most important component of an aquaponic system. The understanding of nitrogen transformations is essential to maintain the water quality, improved fish and plant growth in an aquaponics system.Over the past year, Pak choi (Brassica rapa, sub. chinensis) and Romaine lettuce (Lactuca sativa var. longifolia) (24 plants per raft) and tilapia (Oreochromis sp.) were selected as the growing species. The impacts of hydraulic loading rate (HLR) and dissolved oxygen (DO) on nitrogen transformations in aquaponic systems were investigated. Nitrogen transformations and vegetable yields were studied at four different HLRs (e.g., 1.0, 1.5, 2.0 and 2.5 m/d) and two DO levels in fish tanks (low DO and high DO). Results showed that an HLR of 1.5 m/d (or higher) significantly higher of Pak choi yield in the aquaponic system than at lower HLR (< 1.5 m/d). This could be attributed to relatively high DO in the HLR of 1.5m/d. Moreover, natural abundance of nitrate nitrogen isotopic composition (δ15N) and the nitrogen mass balance confirmed that there was high loss of nitrogen via denitrification process in the aquaponic systems when the fish were fed with 35-50 g/tank/d. δ15N of nitrate at low DO operating condition was higher than that of high DO operating condition. However, the low DO condition was sufficient enough for plant growth. Interestingly, nitrate accumulation or "balloon effect" was observed at all conditions in which nitrogen input was relatively higher than the plant requirement. The results further indicated that the nitrogen utilization efficiency (NUE) could be improved by reducing feed-to-plant ratio. The study of nitrogen transformations in Romaine lettuce-based aquaponic systems is in progress and expected to be completed at the end of 2015. The objectives 1 to2 of nitrogen transformations have so far been completedfor Pak choi. The discovery of balloon effect at high feed-to-plant ratio and the values of natural abundance of nitrogen isotopic composition (indicating the denitrification process in an aquaponic system) are the new knowledge obtained in this study. The information of δ15N values in Pak choi-based aquaponic systems (such as bulk nitrogen in plant's organs, sludge, nitrate in recirculating water and nitrate in plant's organs) werefully characterized. Those isotopic values are the useful baseline to holistically understand the biochemical processes of all species in aquaponic systems. In conclusion, the obtained information quantitatively and qualitatively provide the understanding of nitrogen transformations from the input (fish feed) to the products (vegetables and gases) and suggest the approaches to increase the NUE of aquaponic systems.
Publications
- Type:
Conference Papers and Presentations
Status:
Other
Year Published:
2015
Citation:
Wongkiew, S and Khanal, S.K. (2015) Nitrogen transformations in floating-raft aquaponic systems . Oral presentation, 27th Annual CTAHR and COE Student Research Symposium, University of Hawaii at Manoa, April 11, 2015.
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Progress 09/01/13 to 08/31/14
Outputs
Target Audience: The aquaponic facility has given a tour tosmall business involved in organic farming. Undergraduate and graduate students, and 2 high schoolstudents also toured the facility. Changes/Problems: One of the Co-PIs left the University during summer of 2014. The Co-PI was responsible for stable nitrogen isotope study. The PI has found a local researcheron the campus whois helping out to conduct the isotope study. What opportunities for training and professional development has the project provided? One graduate student, and one undergraduate student have been working on the project. Two high school studentshave also been briefly involved in the project. How have the results been disseminated to communities of interest? We have discussed with organic producer in the state. They visited our facility and are willing to sell the vegetable to the local clients to garner the public acceptance of the products from aquaponic system. What do you plan to do during the next reporting period to accomplish the goals? We will continue to monitor the transformations of different forms of nitrogen in aquaponic systems under optimized conditions. We will initiate stable nitrogen isotope techniqueusing 15N to understand the mechanisms of N-transformation in aquaponic system. The system willbe tested for other plants species, e.g. roman lettuce, chive and tomato.
Impacts
What was accomplished under these goals?
The project continues to provide data on N-transformations. So far we have been able to examine how hydraulic loading rate affects N-transformation, plant yield and DO in the fish tank.So, we have completed Objective 1 for Pak Choi.
Publications
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