Mechanisms and mass transfer kinetics of anammox during sludge enrichment

Mass transfer kinetics for enrichment of anammox granular sludge (AnGS) is important for optimizing the removal of ammonium (NH₄⁺) from wastewater. AnGS enrichment was monitored over 147 days in a continuous upflow sludge bed anammox reactor (CUSBAR) experiment, which was simulated using Generalized Fulazzaky equations to predict the underlying mechanisms and mass transfer kinetics. The removal efficiency of NH₄⁺ followed the bacterial growth progressed through four distinct phases over 63 days, starting with an initial NH₄⁺ concentration of 30.9 mg/L. The CUSBAR process achieved a performance of 84.97 % on the 147th day of the experiment, with the initial NH₄⁺ concentration increased from 30.9 to 75.0 mg/L. The internal mass transfer (IMT) and global mass transfer rates were nearly identical and significantly higher than the external mass transfer (EMT) rate, indicating that EMT was the dominant resistance to mass transfer. The positive correlation between NH₄⁺ removal efficiency and IMT rate provides valuable insights into the dynamic response of AnGS development during the 147-day enrichment period. This study's findings enhance the availability of AnGS as inocula for future CUSBAR process applications, expanding the knowledge base and references in anammox-based nitrogen removal technology.