Objective Constructed wetland systems represent a sophisticated ecological approach to wastewater treatment, where plants, substrates, and microorganisms interact through intricate physical, chemical, and biological processes. Among these components, microorganisms play a pivotal role, particularly in the removal of nitrogen and phosphorus, which are key pollutants in wastewater. This study aims to investigate the impact of different operational conditions on the microbial community structure within a constructed wetland model.

Methods To achieve this objective, the study constructed a wetland system and analyzed the bacterial community structure under three distinct conditions: before pre-tests (J1), horizontal subsurface flow (J2), and tidal flow (J3). These conditions were designed to simulate various real-world scenarios that constructed wetlands might encounter, thereby providing insights into how different flow patterns and initial conditions affect microbial communities.

Results At the phylum level, the analysis revealed that Proteobacteria dominated the bacterial community across all tested conditions, highlighting its ubiquitous presence and potential importance in wetland ecosystems. However, the composition of other bacterial phyla varied significantly between the conditions. Specifically, in the tidal flow condition (J3), the abundance of Cyanobacteria, Verrucobacteria, Bacteroidota, Nitrospirota, Actinobacteriota, Planctomycetota, and Chloroflexi increased compared to the horizontal subsurface flow condition (J2). Conversely, the abundance of Firmicutes and Patescibacteria decreased in J3. At the genus level, the dominant bacteria in the initial group (J1) samples were Lacunisphaera, Kapabacteriales, and Novosphingobium. In contrast, Bacillus emerged as the predominant genus in both J2 and J3 samples. Compared with J2, Luteolibacter, Neochlamydia, Flavobacterium and Novosphingobium were the dominant bacteria in J3 system, and the relative abundance of Nitrospira increased from 3.94% to 5.56%, becoming the second dominant bacteria in wetlands.

Conclusion The reoxygenation capacity of J3 condition improved the dissolved oxygen (DO) content in the wetland, and the bacteria that removed nitrogen and organic matter increased in the dominant bacteria. The total nitrogen (TN) removal rate of J3 condition increased by 92.67% compared with J2 condition. In addition, nitrite nitrogen (\mathrmNO_2^- -N) in J3 condition did not enrich during the experiment and remained at a low level (<0.01 mg/L), indicating that the nitrification reaction in the wetland was good. A good bacterial community of nitrogen and phosphorus removal has been established in the wetland. The results of this study could provide scientific basis for the construction of constructed wetland systems.