Location: Cool and Cold Water Aquaculture ResearchTitle: Fluidization velocity assessment of commercially available sulfur particles for use in autotrophic denitrification biofilters Author
Submitted to: Aquacultural Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/6/2014
Publication Date: 4/1/2014
Citation: Christianson, L., Summerfelt, S. 2014. Fluidization velocity assessment of commercially available sulfur particles for use in autotrophic denitrification biofilters. Aquacultural Engineering. 60: 1-5. dx.doi.org/10.1016/j.aquaeng.2014.03.004. Interpretive Summary: Reducing the amount of nutrients in agricultural outflows is important for increased environmental sustainability of agriculture. We are developing a new technology called a “sulfur-based autotrophic denitrification biofilter” to convert the nitrate in fish farm effluent to benign nitrogen gas, which comprises nearly 80% of the air around us. In common terms, this technology consists of a container (a “bioreactor”) filled with small sulfur particles, through which our aquaculture effluent water flows upwards until the sulfur particles are suspended (“fluidizing” them like in a popcorn popper). First, however, we had to know the characteristics of different kinds of commercially available sulfur materials (“flakes”, “grains” and “powder”) to evaluate how well they would work in one of our biofilters. We determined that the sulfur flake product required flow rates that were too high to be practical in a full size biofilter, while the sulfur powder was difficult to use due to clumping when wet. The sulfur grains provided a happy medium. These results are important to USDA ARS stakeholders because they provide a first step in the evaluation of a potential new water treatment technology. Reducing nutrient outflows from land-based fish farms will become increasingly important to producers as water quality standards and regulatory permitting requirements continue to tighten.
Technical Abstract: There has been no evaluation of sulfur-based autotrophic denitrification using fluidized biofilters in a recirculating aquaculture system to mitigate nitrate-nitrogen loads. The objectives of this work were to quantify the particle size distribution, specific surface area, and fluidization velocities of three commercial sulfur products to provide a proof of concept assessment of the ability of sulfur particles to serve in a fluidized denitrification reactor for nitrate removal from aquaculture effluent. The finest of the products, an elemental sulfur powder with an effective size of 0.08 mm, provided greater bed specific surface area (32,300 m2 m-3) than fine sands typically used in fluidized biofilters, and had corresponding very low fluidization velocities (0.2 cm s-1 at 60% bed expansion). Of the other two sulfur media tested, the granular product (0.30 mm effective size) was slightly more promising as its specific surface area (4110 m2m-3) and superficial velocity to expand 60% (1.87 cm s-1) fell near the reported range often used for fluidized sand. The sulfur flake product (0.95 mm effective size) was not recommended due to high required fluidization velocities (5.0 cm s-1 at 60% bed expansion), relative particle friability, and lower specific surface area (1990 m2m-3). Further investigation of fluidized biofilters for sulfur-based autotrophic denitrification will increase understanding of the nitrate-removal performance and cost efficiency of this innovative concept for reduction of nitrate in aquaculture effluent.