Numerical simulation and nitrogen removal mechanism of a novel airlift dual transverse internal loop reactor
LIU Ye-xing1, YU Li-fang1, CHEN Qian-yi1, DAI Bu-feng2, CAO Wan2, PENG Dang-cong1
1. School of Municipal and Environmental Engineering, Xi'an University of Architecture and Technology, Xi'an 710055, China; 2. Nanjing Municipal Design and Research Institute Co., Ltd, Nanjing 210008, China
Abstract：A novel airlift dual transverse internal-loop (ADTL) reactor was set up and operated for the treatment of synthetic municipal wastewater, aiming to eliminate internal circulation energy consumption of conventional biological nitrogen removal process. The key structural parameters, such as the ratio of top clearance height to liquid level height (Htc/Hl), bottom clearance height/liquid level height (Hbc/Hl) and A/O, were optimized by Computational Fluid Dynamics (CFD) simulation. Subsequently, an optimized ADTL reactor was long-term operated to investigate nitrogen removal performance, functional bacterial activity, enzymatic activity, and microbial community structure characteristics. The CFD numerical simulation results revealed that when the Htc/Hl、Hbc/Hl and A/O were 0.08,0.08 and 1:1, respectively, the liquid circulation velocity and liquid flow uniformity of the ADTL reactor were better. The long-term operating performance of the reactor demonstrated that, in comparison with the conventional internal circulation mode, the ADTL mode achieved an 11.96% increase in total nitrogen removal efficiency. In addition, the ratio of specific nitrite utilization rate to specific ammonia utilization rate (SNUR/SAUR) decreased from 1.71 to 1.13, while the ratio of specific nitrite reduction rate to specific nitrate reduction rate (NIRR/NARR) increased from 0.39 to 0.66. Corresponding trends were also observed in the enzymatic activity ratios. Additionally, Illumina MiSeq sequencing analysis revealed significant increases in the abundance of nitrite-reducing bacteria such as Levilinea (21.58%), Melioribacter (4.54%), and Burkholderia (1.71%) during the ATDL stage. Conversely, the abundance of nitrate-reducing bacteria like Azospira (0%), Denitratisoma (1.49%), and Dechloromonas (0.84%) was relatively low. These findings suggested that the ADTL reactor effectively repulses the nitrite loop associated with conventional internal circulation mode, leading to reduced aeration energy consumption during nitrification and decreased carbon source requirements during denitrification. Therefore, these results demonstrated the potential of the ADTL reactor to enhance the quality and efficiency of municipal wastewater treatment plants, providing valuable technical support for improving wastewater treatment.
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