A tracer study gives vital information on system hydraulic residence time (HRT), flow & mixing patterns, and information on potential short-circuiting. They are useful in a wide variety of applications including aerated lagoons, polishing ponds, and storm water treatment systems. While most people only focus on the discovery of HRT, some of the most vital treatment information comes from information on mixing and potential short-circuiting. In most cases, the basin volume is a “fixed” condition which is not going to change in the short-term. What we can change based on tracer study information is aeration/mixer placement and prove if curtains are needed or effective in their current placement.
A tracer study is done using a “conservative” material that passes through the system without significant adsorption or degradation. In most cases we use a lithium chloride salt or fluorescent dye. The presence and concentration of which can be readily measured using accurate lab procedures. Dosing is based upon generating a target initial concentration and them measuring concentrations at sampling points at set times for two theoretical residence times.
The sample data is then plotted to determine:
1. Time at first appearance
2. Peak concentration time
3. Peak concentration magnitude (amount of tracer)
4. Decrease in tracer concentration (time & pattern)
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