Enhanced Nitrogen and Phosphorus Removal from Alkaline Fermentation Broth by a Novel Modified Zeolite: Mechanisms Revealed by Molecular Dynamic Simulation

Abstract

Nitrogen (N) and phosphorus (P) release during the sludge alkaline fermentation process poses a significant challenge for wastewater treatment, as it limits the effective use of fermentation broth as a carbon source. This study explored the use of hydrochloric acid (HCl)-modified zeolite to enhance the removal of N and P from alkaline sludge fermentation broth. The optimized conditions for HCl modification were determined to be 2.0 mol/L HCl and a zeolite dosage of 100 g/L. The modification resulted in a pore size increase, leading to enhanced adsorption capacities of 90.83% for NH₄⁺–N and 28.52% for PO₄^3––P. Additionally, the modified zeolite reduced the loss of volatile fatty acids (VFAs), retaining over 98 mg COD/L, which was crucial for maintaining the carbon source for further biological treatments. Adsorption kinetics followed a pseudo-second-order model, indicating chemisorption as the primary mechanism. Molecular dynamics simulations revealed that the adsorption process of the modified zeolite was more stable, with stronger hydrogen bonding for NH₄⁺–N and better retention of PO₄^3––P compared with natural zeolite. This study demonstrated the potential of HCl-modified zeolite as an effective adsorbent for improving N and P removal while preserving valuable VFAs in wastewater treatment processes.