Nitrogen removal performance and bacterial community analysis of a multistage step-feeding tidal flow constructed wetland

Mishari Khajah, Franciszek Bydalek, Akintunde O. Babatunde, Abdullah Al-Matouq, Jannis Wenk, Gordon Webster

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7 Citations (SciVal)


A multistage mesocosm vertical flow constructed wetland system was designed to treat synthetic domestic wastewater with a high nitrogen (N) load. The study aim was to determine the impact of design and operational variables on N removal efficiency in such systems. A tidal flow operational strategy enhanced aeration and was coupled with a step-feeding approach to promote N removal. Over the 420-day running period N removal rates were between 70 and 77 gN/m3/d, for a step-feeding ratio range of 60:40 to 80:20. The system was able to remove 91–95% of chemical oxygen demand, 74–91% of ammonium and 66–81% of total-N. Tidal flow and step-feeding strategies significantly impacted nitrogen removal with the best performance at a step-feeding ratio of 80:20 providing a carbon to nitrogen (COD/N) ratio of 4–5. The bacterial diversity increased at each stage throughout the system with dominating phyla Proteobacteria, Firmicutes, Planctomycetes, Bacteroidetes, Chloroflexi, Verrucomicrobia and Acidobacteria. Dominant bacteria at the genus level were Thiothrix, Planctomyces, Azonexus, Pseudoxanthomonas, Hydrogenophaga, Gemmobacter and other genera suggesting that N removal was accomplished via diverse metabolic pathways, including autotrophic nitrification, heterotrophic denitrification, autotrophic denitrification, and possibly anammox. This study shows benefits of step-feeding strategies in tidal flow constructed wetlands as a cost-effective solution for minimizing external carbon input to achieve effective N removal.

Original languageEnglish
Article number1128901
JournalFrontiers in Water
Publication statusPublished - 23 Feb 2023

Bibliographical note

Funding Information:
FB was supported by a Natural Environment Research Council (NERC) PhD studentship at the GW4 Center for Doctoral Training in Freshwater Biosciences and Sustainability (GW4 FRESH CDT, Grant No. NE/RO11524/1).

The authors would like to thank Kuwait Institute for Scientific Research (KISR) for their financial support of this study. Also, special thanks to the technical staff at the Cardiff University School of Engineering and the School of Biosciences Genomics Research Hub.

MK reports financial support was provided by Kuwait Institute for Scientific Research. FB reports financial support was provided by UK Research and Innovation. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Data availability statement
All relevant data is contained within the article: The original contributions presented in the study are included in the article/Supplementary material, further inquiries can be directed to the corresponding author/s.


  • biological treatment
  • carbon dosage
  • microbial structure
  • nature-based solutions
  • nitrification-denitrification
  • nutrients removal

ASJC Scopus subject areas

  • Water Science and Technology


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