(98f) Ammonia Removal from Aquaculture Stocking Water
A continuous membrane system capable of maintaining low levels of total ammonia nitrogen (TAN, 𝑁𝐻3, and 𝑁𝐻4 +) in aquaculture holding and transport vessels is being developed. Ammonia is the major metabolite of fish, therefore, adequate TAN removal is necessary to maintain the health and productivity of aquatic organisms. High levels of ammonia result in the damage of gas exchange tissues, leading to increased mortality and decreased average harvest weight. Membrane systems are desirable for their scalability, lack of compaction and channeling, as in packed beds, and their ability to stabilize additives used during functionalization. Zeolite 13X demonstrates efficient 𝑁𝐻4 + exchange with 𝑁𝑎 + in aqueous solutions. Zeolite 13X is inexpensive and functions well as an ion exchange material with high ammonium exchange capacities. In order to improve the stability of zeolite 13X in water and develop a continuous TAN removal scheme, mixed-matrix membranes have been fabricated in the presence and absence of porogens. Porogens have been used to investigate the effect of pore size and pore density on the membrane structure and the membrane performance. The membranes with porogens exhibited higher flux but lower ammonia removal due to decreased residence time. Porogen-free membranes had a higher ammonia removal capacity due to longer residence time. The ammonia removal capacity was found to correlate well with the amount of zeolite 13X incorporated. An optimal formulation will maximize flux and available zeolite surface area, minimize residence time, and retain large ammonia loadings after a large volume of liquid has been treated.