Removal of nitrogen elements in culture water is one of the major concerns in recirculating aquaculture system (RAS). Maintaining a low concentration of nitrogen compounds is essential for a good quality of aquaculture production. Due to fish is very sensitive to the toxic ammonium/ammonia, nitrification biofiltration tank is often an integrate part of filtration in RAS to remove ammonium via nitrification. However, nitrate accumulation via nitrification in RAS is often observed during the operation, which is usually solved by replacing with the fresh water into the system. With the concern of water consumption, bio-electrochemical system (BES) is introduced in this study to realize simultaneous nitrate removal for the system while generating the electricity through electron transferring. A microbial fuel cell (MFC) with an anion exchange membrane (AEM) was constructed. The removal of nitrate from aquaculture water generated from RAS was achieved by nitrate migration across the AEM and heterotrophic denitrification in the anode chamber. To further investigate the potential application of BES in RAS, the cathode chamber was incubated with biofilm to do the nitrification while the denitrification processing in the anode chamber. The study gave a total inorganic nitrogen removal efficiency of 38.72% ± 4.99, and a COD removal of 86.09% ± 9.83. The average daily electricity generation was 67.98 A m-3 ± 13.91, and nitrate-nitrogen concentration remained at 21.02 ± 2.62 mg L-1 throughout the experiment. These results of treating aquaculture water indicate that BES has a potential to install within RAS for enhanced nitrogen removal. / MS / The demand of aquaculture products is continuously increasing; however, the wastewater discharges from aquaculture systems also brings the environmental concerns. Recirculating aquaculture system is one of the reliable aquaculture systems applies in fish farming, which is able to treat the culture water within the system loop. The ammonia, which is produced and released continuously from deamination of protein, is the primary concern in aquaculture system due to its toxicity. The ammonia/ammonium and can be removed by the nitrification biofiltration part in recirculating aquaculture system. Nitrification process removes ammonia or ammonium to nitrate, which is less toxic to fish. During the operation, nitrate accumulation via nitrification in recirculating aquaculture system is often observed. High level of nitrate in culture water may leads to fish health issues. To have a good quality of aquaculture production, exchanging with the fresh water into the system regularly is needed for the recirculating aquaculture system.
With the consideration of water consumption, bio-electrochemical system was brought in this study to perform simultaneous nitrogen compounds removal for the recirculating aquaculture system while generating the electricity through electron transferring. Microbial fuel cell, which is a form of bio-electrochemical system, with an anion exchange membrane was designed. The microbial fuel cell was constructed with two chambers, which are anode and cathode. The cathode chamber was incubated with biofilm to do the nitrification, whereas the denitrification was processing in the anode chamber to achieve the nitrate removal. Culture water with a certain amount of ammonia/ammonium that obtained from recirculating aquaculture system first entered the cathode chamber of microbial fuel cell, and oxidized to nitrate via nitrification. The generated nitrate in cathode chamber migrated across anion exchange membrane to the anode chamber, and removed via denitrification process to complete nitrogen compounds removal for the entire system.
The study presented a total inorganic nitrogen removal efficiency of 38.72% ±4.99, and a chemical oxygen demand removal of 86.09% ±9.83 from the system. The average daily electricity generation was 67.98 A m⁻³ ± 13.91, and nitrate-nitrogen concentration remained at 21.02 ± 2.62 mg L⁻¹ for the system throughout the experiment period. These results of treating aquaculture water indicate that bio-electrochemical system has a potential to apply within recirculating aquaculture system for enhanced nitrogen removal, while reducing the water consumption and generating the electricity.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/91468 |
| Date | 22 January 2018 |
| Creators | Guan, Lu |
| Contributors | Environmental Science and Engineering, He, Zhen, Kuhn, David D., Wang, Zhiwu |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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