Effects of hydraulic loading rate and substrate on ammonium removal in tidal flow constructed wetlands treating black and odorous water bodies.

• A maximum hydraulic loading rate of 4 m·d−1 was employed in TFCWs. • Zeolite-augmented TFCW enhanced the removal efficiencies of NH 4 +-N and TN. • Adding zeolite changed the microbial community structure and nitrifier's diversity. • Zeolite addition increased nitrification genes but not denitrification genes. • TFCW-Z is a promising alternative for treating black and odorous water bodies. The efficient removal of ammonium nitrogen (NH 4 +-N) is vital to eliminating black and odorous water bodies. In this work, tidal flow constructed wetlands with gravel (TFCW-G) and with a mixture of zeolite and gravel (TFCW-Z) were set up to treat black and odorous water bodies at different hydraulic loading rates (HLRs). Results showed that zeolite significantly enhanced nitrogen removal, and the maximum NH 4 +-N removal efficiency of 96.69% was achieved in TFCW-Z at HLR of 3 m·d−1 with a flooding and drying cycle of 2 h. Zeolite addition changed the microbial community structure and the abundance of nitrification genes. Comammox Nitrospira was the only enriched strain accounting for NH 4 +-N removal in TFCW-G, while the co-occurrence of comammox Nitrospira and the canonical and potential ammonia-oxidizing bacteria were identified in TFCW-Z. Summarily, high performance, together with low footprint and low maintenance cost, are characteristics that make the TFCW-Z a promising and competitive alternative. [ABSTRACT FROM AUTHOR]