Modelling of high-rate activated sludge process: Assessment of model parameters by sensitivity and uncertainty analyses

Hazal Gulhan*, Reza Faraji Dizaji, Muhammed Nimet Hamidi, Amr Mustafa Abdelrahman, Safak Basa, Seyma Cingoz, Ismail Koyuncu, Huseyin Guven, Hale Ozgun, Mustafa Evren Ersahin, Recep Kaan Dereli, Izzet Ozturk

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

1 Citation (Scopus)


The objective of this study is to develop a mechanistic model to predict the long-term dynamic performance of High-Rate Activated Sludge (HRAS) process, including the removal of carbon (COD), nitrogen (N), and phosphorus (P). The model was formulated with inspiration from Activated Sludge Models No. 1 and 3 (ASM1 and ASM3) to incorporate essential mechanisms, such as adsorption and storage substrate, specific to HRAS systems. A stepwise protocol was followed for calibration with dynamic data from a pilot-scale HRAS plant. Sensitivity analysis identified influential model parameters, including maximum specific growth rate (μ), growth yield (YH), storage yield (YSTO), storage rate (kSTO), decay rate (b), and half saturation of the readily biodegradable substrate for growth (KS1). The calibrated model achieved prediction efficiencies above the normalized Mean Absolute Error (MAE) of 70 % for mixed liquor suspended solids (MLSS), total chemical oxygen demand (TCOD), soluble COD (SCOD), particulate COD (XCOD), total nitrogen (TN), ammonia nitrogen (SNH), total phosphorus (TP), soluble TP (STP), and particulate TP (XTP). Uncertainty analysis revealed that SCOD was underestimated. Based on the dynamic profiles of uncertainty bands and observed data, there is potential for improving the estimation of dynamic behavior in STP. The observed discrepancies may be attributed to variations in wastewater characteristics during the monitoring period, particularly concerning the phosphorus (P) fractions of the readily biodegradable substrate (SS) and soluble inerts (SI), which were not considered as dynamically changing parameters in the model.

Original languageEnglish
Article number170102
JournalScience of the Total Environment
Publication statusPublished - 10 Mar 2024

Bibliographical note

Publisher Copyright:
© 2024 Elsevier B.V.


This research was funded by Istanbul Water and Sewerage Administration (ISKI) with the project titled as “Integration of High-rate Activated Sludge Process and Anaerobic Membrane Bioreactor Process for Energy Efficient Wastewater Treatment in Istanbul: Maximum Energy Recovery (MEGA2 Project)”. The authors would like to express their gratitude for the support from the Istanbul Technical University Scientific Research Project Coordination Unit , Turkey, Scientific Research Projects: Hazal Gulhan (Project No: 42469 ), Muhammed Hamidi (Project No: 42690 ), and Reza Faraji Dizaji (Project No: 43103 ).

FundersFunder number
Hazal Gulhan42469
Istanbul Water and Sewerage Administration
Maximum Energy Recovery
Muhammed Hamidi42690
Reza Faraji Dizaji43103
Istanbul Teknik Üniversitesi


    • Adsorption
    • Calibration protocol
    • Dynamic modelling
    • Nutrients
    • Storage


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