Influence of Biological Oxygen Demand Degradation Patterns on W ater-Quality Modeling for Rivers Running through Urban Areas

Water-quality modeling plays a crucial role in the management of aquatic environments, especially in urban river systems. This study aims to investigate the influence of various Biological Oxygen Demand (BOD) degradation patterns on the accuracy of the Streeter–Phelps (SP) equation, a commonly utilized algorithm in water-quality simulations. Employing a comparative approach, the research integrates different degradation models including first-order decay, mixed second-order decay, and oxygen-inhibition decay to simulate the dissolved oxygen (DO) sag profile of a river. Results indicate that the oxygen-inhibition SP equation yields higher estimations of BOD and DO concentrations, while the mixed second SP equation produces lower estimations among the models tested. Field application to the Keelung River shows that both the SP and oxygen-inhibition equations provide similar calculations for BOD and DO concentrations, whereas the mixed second SP equation consistently offers the least estimates. The study identifies pollution loading and atmospheric reaeration constants as critical factors significantly impacting DO levels in aqueous environments. The findings suggest that the mixed second SP equation is preferable when BOD decay trends are rapid, whereas oxygen-inhibition modeling is more accurate in scenarios of slower decay. This research emphasizes the importance of selecting appropriate modeling approaches for effective water-quality management.