Improved nitrogen removal by optimizing the distribution of dissolved oxygen in a simulated constructed wetland system with embedding a water-sealed zone for polishing reclaimed water

• Published in: Journal of water process engineering 2024-05, Vol.62, p.105287, Article 105287
• Main Authors: Zheng, Yu, Zhang, Nan, Zhang, Rongshe, Li, Chenguang, Liu, Zhen, Guo, Yingzi, Zhang, Luning, Wang, Qian, Li, Yuanyuan, Salah, Mohomed, Zheng, Hao, Li, Fengmin
• Format: Article
• Language: English
• Subjects: Bacterial community; Baffled constructed wetlands; Dissolved oxygen; Nitrogen removal; Water flow pattern
• ISSN: 2214-7144; 2214-7144
• DOI: 10.1016/j.jwpe.2024.105287

Reclaimed water reuse is a promising and effective way to alleviate the water resources crisis, but its residual nitrogen poses a high risk to the receiving water bodies. Constructed wetlands (CWs) have been increasingly used to remove nitrogen from reclaimed water. Due to the high concentration and uneven distribution of dissolved oxygen in single-stage CWs, the removal of total nitrogen (TN), especially nitrate‑nitrogen (NO3−-N), in reclaimed water is limited. In this study, a novel filter system modeling CW was constructed by setting baffles to embed in a water-sealed zone. The results showed that the presence of the water-sealed zone not only delayed atmospheric reoxygenation but also extended the flow path, thereby simultaneously increasing the ammonium-nitrogen (NH4+-N) and NO3−-N removal rates (TN removal rate from 49.9 % to 68.4 %). The nitrifiers (Nitrospira), denitrifiers (Pseudomonas, Thermomonas, and Thiobacillus), and anammox bacteria (Candidatus Anammoximicrobium) were simultaneously enriched in novel filter system. The co-occurrence network of functional bacteria in the novel filter system was simpler and clearer, and bacterial cooperation accounted for more than competition. Furthermore, the transformation of dissolved organic matter showed an obvious correlation with nitrogen removal, that is, tyrosine-like can be degraded as an endogenous carbon source for denitrification and at the same time produce humic acid-like components. Although the filter systems used here cannot be fully considered as CWs due to the lack of plants, this work still provides a novel strategy for the design and optimization of CW structures to achieve further removal of TN from reclaimed water. [Display omitted] •The novel baffled filter system with embedding a water-sealed zone was constructed.•The water-sealed zone delayed atmospheric reoxygenation and extended the flow path.•The baffled filter system simultaneously promoted NH4+-N and NO3−-N removal.•The baffled system showed a simpler and more cooperative co-occurrence network.•The transformation of DOM showed a correlation with nitrogen removal.