Abstract:
Instream water quality management encompasses field monitoring and utilisation of mathematical models. These models
can be coupled with optimisation techniques to determine more efficient water quality management alternatives. Among
these activities, wastewater treatment plays a crucial role. In this work, a Streeter-Phelps dissolved oxygen model (DO) is
implemented in a semi-hypothetical Upper Olifants River system to forecast instream dissolved oxygen profiles in response
to different wastewater discharge scenarios. A mixed integer programming (MIP) numerical approach was used in the
simulation and determination of the best treatment regimen to meet the instream DO standard at the minimum cost for the
chosen river catchment. The Olifants River catchment modelled in this study features 9 wastewater treatment plants. Three
treatment levels were evaluated for biochemical oxygen demand (BOD) and the impact was evaluated at specific measuring
points (checkpoints) within the river system. Using this model, it was demonstrated that water quality standards can be met
at all monitoring points at a minimum cost by simultaneously optimising treatment levels at each treatment plant.
