Nitrogen removal and its relationship with the nitrogen-cycle genes and microorganisms in the horizontal subsurface flow constructed wetlands with different design parameters

ABSTRACT

This study aims to investigate nitrogen removal and its relationship with the nitrogen-cycle genes and microorganisms in the horizontal subsurface flow constructed wetlands (CWs) with different design parameters. Twelve mesocosm-scale CWs with four substrates and three hydraulic loading rates were set up in the outdoor. The result showed the CWs with zeolite as substrate and HLR of 20 cm/d were selected as the best choice for the TN and NH₃-N removal. It was found that the single-stage mesocosm-scale CWs were incapable to achieve high removals of TN and NH₃-N due to inefficient nitrification process in the systems. This was demonstrated by the lower abundance of the nitrification genes (AOA and AOB) than the denitrification genes (nirK and nirS), and the less diverse nitrification microorganisms than the denitrification microorganisms in the CWs. The results also show that microorganism community structure including nitrogen-cycle microorganisms in the constructed wetland systems was affected by the design parameters especially the substrate type. These findings show that nitrification is a limiting factor for the nitrogen removal by CWs.

KEYWORDS:

• Constructed wetland
• denitrification
• nitrification
• nitrogen-cycle genes
• nitrogen-cycle microorganisms
• nitrogenous substances

Funding

The authors would like to acknowledge the financial support from Guangzhou municipal government (20150401007 and PC2015) and the Chinese Academy of Sciences (KZZD-EW-09). This is a Contribution No. IS-2368 from GIG CAS.