ORP-Guided, Temperature-Model-Based Control of Nitrification and Denitrification in SBRs and a Full-Scale UNITANK...

This study evaluated the efficacy of oxidation-reduction potential (ORP) as a real-time control parameter for optimizing nitrification and denitrification durations in a sequencing batch reactor (SBR) treating actual municipal wastewater. The distinct novelty of this work lies in the systematic validation of characteristic ORP inflection points using real municipal wastewater with inherent compositional variability, the derivation of temperature dependent predictive models from a robust dataset, and the successful scale-up of the control strategy to a full-scale UNITANK system bridging a critical gap between laboratory research and practical implementation. Characteristic inflection points on the ORP profile were identified: A distinct knee point within 28-80 mV indicated the completion of nitrification (> 95% NH₄ ⁺-N removal), while a stable plateau (|dORP/dt| ≤ 0.1 mV/min) within -25 to -65 mV signified the end of denitrification (> 90% total nitrogen removal). Temperature exhibited the most significant influence on reaction rates. Linear regression models predicted phase durations: nitrification time (min) = -11.918 × T (°C) + 370.3 (R² = 0.82) and denitrification time (min) = -7.363 × T (°C) + 274.93 (R² = 0.75). Implementation of this temperature-model-based strategy (with ORP used only for validation and calibration) in a full-scale UNITANK system reduced aeration time and achieved annual energy savings of approximately 6000 kWh (a 25% reduction), while maintaining effluent quality. These findings confirm the feasibility and economic advantage of using ORP as a guiding rather than direct real-time control parameter for intelligent management of biological nitrogen removal.