Study of biological nitrification kinetics under harsh environmental conditions

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Date

2023-12-20

Authors

Abbaszadeh, Leila

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Abstract

Nitrification has been widely applied in wastewater treatment, however gaining more in-sight into the nitrifiers’ physiology and stress response is necessary for the optimization of nutrients removal and design of advanced processes. The primary focus of our thesis can be divided into three main parts. In the first section of this thesis, the process of biological nitrification of the leachates produced by the local municipal solid waste landfill in Patras, Greece is studied. For this purpose, populations of nitrifying bacteria were isolated, and exposed to an environment of different concentrations of leachate. The experimental results showed an increase in the retarding action of the leachate, in nitrification, with an increase in its concentration in the feed. Finally, with the use of the Aquasim platform, an attempt is made to estimate the kinetic parameters that characterize the nitritification and nitratification reactions. Since nitrification initiates with ammonia oxidation performed by ammonia-oxidizing bacteria (AOB), in the second part, the purpose of study was to investigate the effects of short-term ammonia starvation on nitrogen uptake and transformation efficiency, as well as the per-formance of starved nitrifiers under various initial substrate concentrations and pH values. Ammonium deprivation for 3 days resulted in fast ammonium/ammonia accumulation upon nitrogen availability, with a maximum uptake rate of 3.87 mmol gprotein -1 min-1. Furthermore, a delay in the production of nitrate was observed with increasing starvation periods, resulting in slower recovery and lower nitrification rate compared to non-starved cells. The maximum ni-trogen accumulation capacity observed was 8.51% (w/w) independently of the external nitrogen concentration, at a range of 250–750 mg N L-1, while pH significantly affected ammonia oxi-dizers’ response, with alkaline values enhancing nitrogen uptake. In total, ammonia accumula-tion after short-term starvation might serve as an important strategy that helps AOB restore their activity, while concurrently it could be applied in wastewater treatment for effective ni-trogen removal and subsequent biomass utilization. In the last part of the present study, a comprehensive mathematical model was developed to describe the nitrification process in mixed cultures involving isolated NOB and starved AOB. The growth equation for NOB was divided into anabolism and catabolism, elucidating the key substrates driving their metabolic activities. Considering the ammonia starvation ef-fect, a single cell-based model was developed to capture the mass transfer phenomena across the AOB cell membrane. This addition allowed for a more accurate representation of the bio-logical dynamics during starvation conditions. The model’s accuracy was validated using ex-perimental data that was not used in the model calibration step. The prediction’s coefficient of determination (R2) was estimated at 0.9. By providing insights into the intricate mechanisms underlying nitrification, this model contributes to the advancement of sustainable wastewater treatment practices.

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Keywords

Nitrification, Starvation

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