Location: Cool and Cold Water Aquaculture ResearchTitle: US researchers study effectiveness of Fluidized Sand Biofilters Author
Submitted to: Hatchery International Magazine
Publication Type: Trade Journal
Publication Acceptance Date: 3/1/2008
Publication Date: 3/1/2008
Citation: Davidson, J., Summerfelt, S. 2008. US researchers study effectiveness of Fluidized Sand Biofilters. Hatchery International Magazine. p.37. Interpretive Summary:
Technical Abstract: Intensive aquaculture facilities generally produce two separate waste flows: 1) a high volume dilute discharge from culture tanks or pump sumps, and 2) a moderately small and solids-concentrated discharge typically backwashed from mechanical filtration units. The high volume dilute flow can appear pristine but can still contain dilute concentrations of a variety of dissolved pollutants, including carbonaceous biochemical oxygen demand (cBOD), total ammonia nitrogen (TAN), total phosphorous, total suspended solids (TSS), and coliform bacteria. Although these water quality constituents are diluted, the cumulative loading of these wastes can be significant. Environmental regulations often govern the cumulative loading and mass loading of these wastes within aquaculture effluents; therefore, effective technologies are needed to treat dilute effluents flowing from aquaculture facilities. We published a peer review article in Aquacultural Engineering 39 (2008) 6-15, suggesting that fluidized sand biofilters (FSBs) can be used to effectively reduce TAN, BOD, and coliform bacteria within a dilute effluent flowing from flow through and partial reuse tanks that were used to culture rainbow trout. The FSB's removed 86-88% TAN, 66-82% cBOD, and 94-98% coliform bacteria. The fluidized sand biofilters also removed small amounts of phosphorous and TSS during short term cleaning events when TSS peaked in the effluent. A submersible pump was used to control biofilm growth and sand level within the biofilter. The pump recirculated biofilm coated sand from the top of the sand bed to the bottom, thus shearing excess biofilm and controlling the sand bed height. However, the pumps were abraded and damaged over time by the sand. Therefore, more robust options such as diaphragm or air lift pumps need to be evaluated for future application. The pump biofilm shearing method required substantially less labor as compared to a siphoning and sand wash/replacement method, and also resulted in greater waste removal efficiencies. Fluidized sand biofilters offer some advantages as a waste treatment option for dilute effluents. In comparison to some of the typical waste treatment options currently used such as sedimentation basins, submerged biofilters, and wetlands, FSBs occupy a much smaller footprint and FSBs produce better TAN and cBOD removal efficiencies. FSBs could be effectively used as a waste treatment option in order for aquaculture facilities to meet discharge standards and minimize negative environmental impacts.