Parameters: Fluorescent Dye Tracing
The St. Anthony Falls Laboratory (SAFL) is a teaching and research facility of the Department of Civil Engineering, University of Minnesota. Their goal is to advance the knowledge and understanding of environmental hydraulics, turbulence, earthscape evolution, and climate/ecosystem dynamics via high quality experimental, theoretical and computational research. As a group, they are committed to transferring that knowledge to the engineering community and to the public through applied research and outreach activities.
Ben Erickson is one of the scientists at SAFL, and is considered the "fluorometer guru" of the laboratory due to his extensive experience with the Turner Designs line of fluorometers. Ben and his colleagues utilize the 10AU and SCUFA fluorometers to conduct hydraulic experiments using rhodamine WT dye as a fluorescent tracer. The information learned in their dye tracing experiments is then applied to solving real life hydraulic issues.
One of the recent issues that the SAFL is currently working on is the feasibility of an emergency sewage storage system for overflows caused by above average amounts of rain runoff in an urban location. To investigate the feasibility, Ben and his team conducted experiments on a smaller scale system that resembled the location under investigation. The key questions that required the use of our fluorometers was how to best set up an aeration system for sewage treatment. The fluorometers were used to quantify diffusion and dispersion in and around a deep bubble column.
To investigate the aeration set-up, the SAFL placed submersible aerators at strategically placed locations on the bottom of the experimental water system. Slugs of rhodamine WT tracer dye were then released at the bottom of the system, while the 10AU and SCUFA Fluorometers monitored its concentration at various points in the water column. With the data from multiple trials, estimates were made on the rate that a bubble column would entrain the surrounding water.
To address the gas exchange questions, the experiment took the data from the previous entrainment experiments and decided on a reasonable flow rate to inject of the test solution. Known flow rates of the conservative tracer rhodamine WT and a volatile tracer were then added at the bottom of the water column. Once at a steady state, water samples were collected and analyzed utilizing fluorometers and gas chromatography yielded data indicating how much tracer gas escaped from solution into gas. The flourometers were used both in the final analysis and during the course of the experiments. They proved quite valuable by allowing the researchers to look at the real time data as the experiment progressed.
With the amount of useful data generated from these experiments and the fluorometers, Ben considers the research project to be an overall success. This information will soon be transferred to the engineering community to enable them to make sound decisions on the emergency sewage storage system project. To learn more about the exciting research that goes on at SAFL, please be sure to visit their website.
Author: Dr. Ben Erickson
Institution: The St. Anthony Falls Laboratory (SAFL), St. Anthony Falls, Minnesota, USA