Tracer Test

By De

Yesterday was a holiday so we had a three day weekend to go exploring.  In order to make use of the long weekend in the lab, Chol decided it would be a good time to run a tracer test in order to see the average retention time the water spends in the columns we are using.  This can be done by "spiking" the wastewater that we intend to pump through the system with sodium chloride.  This addition will increase the electrical conductivity of the water and can be monitored using an EC monitor.  The EC records data on 10 minute intervals.  When the EC begins to increase then level off, the "spiked" water has gone completely through the system.

We can calculate a theoretical value for the average detention time in the column:
            avg detention time= EBCT*porosity
           (EBCT= empty bed contact time)
            EBCT= Volume/Q=Height/Velocity
for the columns the theoretical EBCT was 4 days, then multiplied by the measured porosity of the sand= 0.4 -----> the average detention time for the columns= 1.6 days

The measured value we got by monitoring the EC of the water came out to be:
   for column 1: 1.302 days
   for column 2: 1.469 days