Computational Fluid Dynamics (CFD) was applied to an intermittent anoxic/aerobic Moving Bed Biofilm Reactor (MBBR) operated under six different aeration intermittency cycles and dissolved oxygen concentration levels. Experimental results showed that most aeration cycles did not provide a sufficiently long anoxic phase to sustain effective denitrification, thereby limiting NOx removal efficiency. This behavior was not adequately captured by simulations performed using conventional biological models (BioWin), which rely on the assumption of complete mixing. In contrast, the CFD model implemented in ANSYS Fluent 2024 R2 enabled a detailed characterization of reactor hydrodynamics and the identification of several inefficiencies, including short-circuiting, back-mixing, and the presence of dead zones. Notably, the simulations revealed a pronounced asymmetric distribution of carriers within the reactor, with the majority accumulating along one side, leaving a significant fraction of the reactor volume largely unoccupied. Further analysis indicated that this phenomenon was caused by a design flaw—specifically, the asymmetric placement of the aerators—combined with an excessively high air injection flow rate.

Optimal Micropollutants Removal, Minimal Bromate Formation, and Improved Effluent Quality for the Eindhoven WWTP by Integrating Biological and Ozonation...

This paper addresses the critical issue of nitrous oxide (N2O) emissions from wastewater treatment plants, which have a significant impact on climate change. The article discusses the challenges associated with measuring and mitigating N2O emissions, as well as the importance of understanding the complex pathways through which N2O is produced in wastewater treatment processes. The article places a special focus on the role of modeling tools in enhancing our understanding of N2O emissions and supporting mitigation strategies. Various modeling approaches, including mechanistic models, data-driven models, and integrated computational fluid dynamics-biokinetic models, are discussed in the context of predicting and controlling N2O emissions. Case studies and examples from real-world applications demonstrate the effectiveness of modeling approaches in identifying emission hotspots, optimizing process control strategies, and developing mitigation measures. Overall, the article emphasizes the significance of modeling in addressing the challenges of N2O emissions in the water sector and advancing sustainability goals.

With increased commitment from the international community to reduce greenhouse gas (GHG) emissions from all sectors in accordance with the Paris Agreement, the water sector has never felt the pressure it is now under to transition to a low-carbon water management model. This requires reducing GHG emissions from grid-energy consumption (Scope 2 emissions), which is straightforward; however, it also requires reducing Scope 1 emissions, which include nitrous oxide and methane emissions, predominantly from wastewater handling and treatment. The pathways and factors leading to biological nitrous oxide and methane formation and emissions from wastewater are highly complex and site-specific. Good emission factors for estimating the Scope 1 emissions are lacking, water utilities have little experience in directly measuring these emissions, and the mathematical modelling of these emissions is challenging. Therefore, this book aims to help the water sector address the Scope 1 emissions by breaking down their pathways and influencing factors, and providing guidance on both the use of emission factors, and performing direct measurements of nitrous oxide and methane emissions from sewers and wastewater treatment plants. The book also dives into the mathematical modelling for predicting these emissions and provides guidance on the use of different mathematical models based upon your conditions, as well as an introduction to alternative modelling methods, including metabolic, data-driven, and AI methods. Finally, the book includes guidance on using the modelling tools for assessing different operating strategies and identifying promising mitigation actions. A must-have book for anyone needing to understand, account for, and reduce water utility Scope 1 emissions. ISBN: 9781789060454 (Paperback) ISBN: 9781789060461 (eBook) ISBN: 9781789060478 (ePub)