Pilot design and modeling of the A2O process for cell growth kinetics to increase the efficiency of organic and nutrient removal from Pardis city wastewater

Subject Areas : Assessing the risks of pollutants on environment

Mojtaba Darzi Daronkola ¹ , Amir Hossein Mahvi ² , Bahman Ramavandi ³ , Seyed Enayat Hashemi ⁴ , Fazel Amiri ⁵

1 - Department of Environmental Engineering, Water and Wastewater Department, Bu.C., Islamic Azad University, Bushehr, Iran
2 - Department of Environmental Health Engineering, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran
3 - Department of Environmental Health Engineering, Faculty of Health and Nutrition, Bushehr University of Medical Sciences, Bushehr, Iran
4 - Department of Environmental Health Engineering, Faculty of Health and Nutrition, Bushehr University of Medical Sciences, Bushehr, Iran
5 - Department of Environmental Engineering, Water and Wastewater Department, Bu.C., Islamic Azad University, Bushehr, Iran

Received: 2025-04-30 Accepted : 2025-05-13 Published : 2025-08-19

Keywords: Kinetics coefficients, A2O process, Organic matter, Nutrient,

Abstract :

A₂O wastewater treatment is actually an upgrade of the activated sludge process with extensive aeration, where two anaerobic and anoxic units are added to remove nitrogen and phosphorus, and the sludge is returned from the settling tank to the anaerobic unit. There is also a return line from the aeration unit to the anoxic tank. Obviously, not all environmental conditions affecting substrate consumption and microbial growth rate may be possible, and controlling factors, such as pH and nutrients, is necessary to provide effective treatment. The rate of substrate consumption in biological systems can be modeled based on the Monod relationship for soluble substrates. Pilot design is based on hydraulic retention time (HRT) according to existing references. After launching the mentioned pilot with real wastewater, biological processes are used to create and maintain stable conditions in the reactors. In this study, raw wastewater, aeration pond, effluent, secondary sedimentation, and activated sludge were collected with 500 samples and the qualitative parameters of COD, BOD₅, TSS and VSS (as dependent variables) were measured. Hence, to measure organic parameters and solids, 100 samples were taken from each of these cases: the aeration tank, the returned activated sludge, the incoming raw sewage, the effluent sedimentation, and secondary sedimentation. In kinetic study, Ks was determined to be 27.9 g COD/m³, µH as 4.4 1/day, bH as 0.0085 1/day and YH as gCOD XH /(gCOD SS) as 0.42. Based on the findings, the synthetic coefficients in the Lineweaver-Burk and Hanes models are suitable, but in the Hofstee model, the amount of K and K_d is lower than the optimal amount for the proper exploitation of the pilot. The efficiency coefficient and the growth rate were also found to be lower than the optimal level.

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