Environmental Engineering Reference
In-Depth Information
Figure 14.8.
Oxygen injection unit locations (circles), pipeline and storage tank (T).
output of 15 TeO
2
per day. The oxygen supply infrastructure was completed in
April 2001, and artificial oxygen injection commenced the following June.
Major modifications to the injection nozzles were undertaken during the
summer of 2001 to position the oxygen stream in the optimal vertical and
horizontal trajectory, which was determined via experimentation. Field trials
involved taking O
2
measurements from the surface and down through the
water column at 1-m intervals. These profiles were taken at 10-m intervals
across a horizontal grid. The number of nozzles (one or two) and their depth
was altered as was the vertical and horizontal angle of the nozzles. Overlap
between the units was minimised where possible. In addition the prevailing
clockwise circulating current within the Turning Basin was utilised to further
aid dispersion and mixing. Three-dimensional oxygen concentration contour
plots for each nozzle configuration were created and visually assessed. It is
believed that the current nozzle configuration maximises mixing and, there-
fore, dissipation of oxygen within the application area. A single injection unit
was observed to increase bottom water oxygen concentrations to 4mg L
1
within a 180-m radius with a secondary zone extending for up to 360m (to
the opposite bank of the Turning Basin) where an increase in oxygen concen-
tration was seen (APEM
2000
); water circulation patterns were also enhanced.
SOD in the MSC upstream of Mode Wheel Locks has, in general, reduced
since 1989 (APEM
1999
,
2000
). However extremely high peak values still occur
within the MSC and are continuing to contribute substantially to the overall
oxygen demand. It is not known what effect the oxygen injection system will
have on SOD over the long term, though we suggest that little reduction will be
observed due to the continual 'rain' of organic material and the anoxic nature
