Investigation of nitrogen conversion efficiency in hydrogen-based autotrophic nitrate reduction reactor

Abstract

This study investigates the performance of a hydrogen-based membrane biofilm reactor (MBfR) for nitrogen transformation over an extended operational period exceeding 200 days. During operational monitoring, the reactor sustained highly alkaline conditions with pH consistently exceeding 11.20, while achieving an ammonia conversion efficiency above 60 % and maintaining a nitrite accumulation rate below 1 %. Integrated mass balance calculations and microbial community profiling revealed the coexistence of denitrification and dissimilatory nitrate reduction to ammonium (DNRA) pathways within the nitrogen transformation network. A factorial experimental design was implemented with hydraulic retention time (HRT) and influent nitrate concentration as independent variables, generating nine distinct operational regimes through cross-variable permutations. Subsequent analysis of extensive experimental datasets enabled the development of a Response Surface Methodology (RSM) model to simulate nitrogen conversion dynamics. Model validation confirmed the statistical reliability and predictive accuracy of the RSM framework. Critical analysis demonstrated that ammonia conversion efficiency in the hydrogen autotrophic nitrate reduction system exhibited significant correlation with individual variables themselves but showed negligible dependence on their interactive effects. These findings provide novel insights into process optimization strategies and theoretical understanding of nitrogen convention.