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GPS-X Technical Reference

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183 Suspended Growth Models<br />

Special 2-D Greyscale Display Variables<br />

The oxidation ditch has a series of special two-dimensional display variables that are<br />

desiged to be displayed on 2-D greyscale outputs. These variables are found in the 2-D<br />

Grescale Ditch Output display variables menu. These graphs show a plan-view of the<br />

oxidation ditch, with tank #1 in the lower right hand corner, and the effluent point in the<br />

upper-right hand corner (the actual influent point depends on the setting in the influent<br />

fractions menu). The flow moves clockwise around each ditch.<br />

Five different variables are available for output: Dissolved oxygen (DO), Ammonia,<br />

Nitrate, Oxygen uptake rate (OUR) and, Denitrification rate (DNR)<br />

Figure 6-22 shows an example of the 2-D greyscale DO graph for a typical oxidation<br />

ditch.<br />

Figure 6-22 - 2-D Greyscale Oxidation Ditch Output - Dissolved Oxygen<br />

Please Note: Due to the high recycle rate within the object (and subsequent short HRTs<br />

for each section of the ditch), the oxidation ditch model often will take longer than<br />

normal to converge to steady-state with the steady-state solver. You may find it<br />

necessary to increase the iteration termination criteria and/or the damping factor on<br />

final approach in the steady-state solver menu to achieve a reasonable solution.<br />

If you are having difficulty with steady-state solutions, you can halt the steady-state<br />

solver at a higher iteration termination value, and run a short dynamic simulation to test if<br />

the steady-state solver solution is adequate. If the dynamic solution does not diverge<br />

appreciably from the steady-state conditions, then the higher iteration termination value is<br />

suitable. If you have any questions or problems, please contact us for assistance at<br />

support@hydromantis.com<br />

<strong>GPS</strong>-X <strong>Technical</strong> <strong>Reference</strong>

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