Constructed wetlands, simulating purification of natural wetlands, have become widely applied technique and valuable complemet to traditional wastewater treatment systems in recent years. Low cost, convenient operation and maintenance and high wastewater treatment efficiency are the major advantages of constructed wetland . Although the quantities of constructed  wetklands have increase year by year, the nitrogent (N) treatment performance  has always been unsatisfactory, which is a major challenge for constructed wetlands.

Oxygen supply has been commonly perceived as a limiting factor to N removal efficiency. The use of constructed wetlands could overcome this problem because of its unique structure, consisting of a down-flow chamber and up-flow chamber. Therefore, the U-shaped flow structure of integrated vertical-flow constructed wetlands  gave rise to the alternating “aerobic-anoxic-anaerobic=anoxic-aerobic” multifunction layer, i.e., a gradient of physical, chemical and biological condition favorable for microbial growth and reproduction. This is especially important for enhancing the function of N removal  bacteria whose oxigent requirement is different.

The competition of N removal microbes in the environtments is the key issue for the nitrogen removal pathway. Moreover, the influent C/N ratio also played a crucial role in denitrification which is ussually restricted by thje lack of organic carbon source. Very few studies have been focused on the relationship between N removal microbes and influent C/N ratio (2:1, 4:1,6:1 and 8:1) nad to reveal the link berween the functional genes of microbes and N conversion reactions. The qPCR technologywas employed to quantify the abundance of key functional genes involved in N removal.


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