Long-Term Operations Modeling: When Does Validation Become Recalibration?

The Metro Wastewater Reclamation District first began using a plant-wide model nearly a decade ago, in anticipation of regulatory changes and the implementation of new processes at its Robert W. Hite Treatment Facility in Denver, Colorado. The District is currently engaged in a 1.3 billion capital improvements plan. This paper presents the method by which the model was calibrated and validated through multiple sampling efforts, and presents full-scale examples of centrate management and treatment. After implementing controlled centrate return, the District's Model User Group found it more practical to recalibrate the model to take into account the improved performance rather than adding a layer of complexity to model inputs. The paper also discusses the different approaches that the District takes for design versus operations modeling, and presents the method in which the District maintains and updates the model.