Bioregeneration of Chabazite During Nitrification of Centrate from Anaerobically Digested Livestock Waste: Experimental and Modeling Studies.

Nitrification of high total ammonia nitrogen-strength wastewaters is challenging due to free ammonia (FA) inhibition of nitrification. FA inhibition can potentially be alleviated by temporarily adsorbing ammonium (NH4+) to natural zeolite, such as chabazite, followed by direct zeolite bioregeneration via nitrification. In this research, the effectiveness of chabazite addition for reducing nitrification inhibition during treatment of centrate from anaerobic digestion of swine waste was quantified. A mathematical model was developed that accounts for ion exchange of NH4+ and sodium at the chabazite surface, surface diffusion of adsorbed NH4+ within the chabazite grains, sequential nitrification of aqueous NH4+ to nitrite and nitrate, and inhibition of nitritation and nitratation rates by NH4+. The model was calibrated using results of abiotic ion exchange and nitrification studies. Subsequently, nitrification tests were carried out with synthetic wastewater with a NH4+-N concentration of 1000 mg L-1, with and without chabazite. A chabazite dose of 150 g L-1 decreased the FA concentration to below the inhibitory level and increased the nitrification rate from 0.16 to 0.36 mg-N (g-VSS)-1 h-1. Following calibration, the model could predict the experimental data with no additional fitting parameters or parameter adjustment, in both the presence and absence of chabazite. The results suggest that the mathematical model provides a theoretically sound conceptual understanding of ion exchange assisted nitrification.