Evaluation of Nitrogen Removal Process by Degradation Kinetics, Microbial Composition, and Functional Gene Expression in an Aerobic Fluidized Bed Biofilm Reactor at Different Carbon to Nitrogen (C:N) Ratios

Abstract

Mechanism of nitrogen removal in the aerobic fluidized bed biofilm reactor was explored by analyzing the nitrogen removal process, degradation kinetics, and microbial characteristic. Carbon to nitrogen (C:N) ratio significantly (0.616**≤R≤0.878**) changed the treatment efficiency of COD_cr, TN, and NH₄ ⁺-N. Moreover, the average removal of NH4+-N and TN under the condition of C:N=13.94 were higher (73.2% and 72.7%) than other conditions. High C:N ratio improved the SND rate (98.8%) in the system. The pollutant degradation conformed to Haldane fictitious kinetic model. Actinobacteria and Protrobacteria were detected and known as dominant species. Additionally, low C:N ratio could increase the relative abundance of Protrobacteria (43.5%). The real-time quantitative PCR results indicated that high C:N ratio increased the SND by enhancing the nirS, nirK, and AMX gene expression. These finds showed that high C:N ratio could enhance the nitrogen removal by improving the gene expression of denitrification and anammox.

Keywords: C:N, Nitrogen removal, Wastewater treatment, degradation kinetics, functional gene