Fluidization velocity assessment of commercially available sulfur particles for use in autotrophic denitrification biofilters

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 0.08mm, provided greater bed specific surface area (32,300m²m^-3) than fine sands typically used in fluidized biofilters, and had corresponding very low fluidization velocities (0.2cms^-1 at 60% bed expansion). Of the other two sulfur media tested, the granular product (0.30mm effective size) was slightly more promising as its specific surface area (4110m²m^-3) and superficial velocity to expand 60% (1.87cms^-1) fell near the reported range often used for fluidized sand. The sulfur flake product (0.95mm effective size) was not recommended due to high required fluidization velocities (5.0cms^-1 at 60% bed expansion), relative particle friability, and lower specific surface area (1990m²m^-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.