Performance and optimization of biological nitrogen removal process enhanced by anoxic/oxic step feeding

The aim of this paper is to investigate the performance and optimization of an biological nitrogen removal process enhanced by the anoxic/oxic four stages step-feeding process under sufficient/insufficient influent carbon source. The concept of influent flow distribution ratio (λ) was introduced according to the performance of the step-feed process for inflow splitting and volume distribution. Under the condition of sufficient carbon, the uniform influent flow distribution ratio was proposed from the standpoint of which is easy for process control, operation optimization and management. Under the condition of different influent C/N ratios, the optimal influent flow distribution ratios (λopt) were determined, by trial-and-error method. The results showed that more than 95.81% of the total nitrogen removal efficiency could be achieved by step-feeding process with a fixed influent C/N ratio. A model was introduced to derive the relationships of total nitrogen removal efficiency with λ and influent C/N ratio. When the influent carbon source was insufficient, however, the λopt between two adjacent stages should not be uniform. The results also showed that the four-stage step-feeding process with λopt of 2.0:2.1:2.5:3.4 could significantly improve the total nitrogen removal efficiency. The results obtained in this study will help to optimize the design and the operation of BNR systems.