Surface TAN Conversion Rate (Reduction in Energy Consumption Using Moving Bed Biofilter)

Land-based reuse systems offer many advantages over netpens or flow-through systems. This includes reduced siting problems, better control of water quality, and optimization of growth rate and production. The primary disadvantages of reuse systems are higher energy use, carbon dioxide emissions, and capital costs. One of the most expensive unit processes in reuse systems is nitrification, the bacterial conversion of ammonia to nitrate. Typical nitrification systems involve pumping of the process water up 3-5 meter through a series of closed reactors using plastic beads or sand as the bacteria support media. A relatively new development is the moving bed filter, a system that uses small floating plastic media that are keep in circulation with mechanical mixing or diffused aeration.

This project will integrate the moving bed biofilter and circular rearing tanks in order to significantly reduced the energy consumption and the size of the reuse system. This will involve the construction of an unique rearing unit/biological filter where the water moves horizontally through the biological filter and back into the rearing unit using airlift pumps with differential heads in the range of 3-4 cm. Both laboratory measurements and numerical modeling will be used in this research. The nitrification performance will be measured as a function of mixing velocity, head losses, and dissolved oxygen levels. Laboratory measurements will be used to validate a numerical model of the flow based on STAR-CCM+, a commercial Computational Fluid Dynamics code. Once validated, the CFD model will be used to investigate scenarios to promote nitrification and how reduce energy use. A prototype system will be constructed and evaluated in terms of fish growth, mortality, and water quality.

This work will be conducted by NWFSC staff in cooperation with Dr. Jim Liou, Department of Civil Engineering, University of Idaho. The project webpage, peer reviewed articles, popular press articles, field demonstration days, and presentations at aquaculture meetings will inform stakeholders of the projects progress and provide a mechanism to rapidly distribute relevant information during the life of the project. 1440Qfilter(TANin-TANout)/Amedia