Nitrogen removal and distribution of ammonia-oxidizing and denitrifying genes in an integrated constructed wetland for swine wastewater treatment

Abstract

This study investigated nitrogen (N) removal process and microbial community distribution in a full-scale integrated constructed wetland (ICW), which was constructed with a bioreactor (R) and three wetland units (W1, W2, and W3) arranged successively along the flow path. For swine wastewater treatment, ICW showed high N removal efficiency with average removal rate of 98% for NH4+-N and 96% for total nitrogen (TN) from August 2012 to July 2014. In ICW sediments, abundance of amoA gene of ammonia-oxidizing archaea (AOA) was 1 order of magnitude greater than ammonia-oxidizing oxidizing bacteria (AOB), and narG gene was 2 orders of magnitude greater than nosZ. The highest amoA gene abundance of AOA and AOB in R were consistent with the most efficient NH4+-N and TN removal compared to W1, W2, and W3. Both W1 and W3 vegetated with Myriophyllum aquaticum had significantly higher AOA abundance than W2 vegetated with Ipomoea aquatica, Zizania latifolia, and Nasturtium officinale (p<0.05). Responding to the increasing NO3−-N concentrations along the flow path, higher narG and nosZ abundance were observed in W2 and W3 than in R and W1. Principal component analysis revealed that there were clear differences in the relative abundance of terminal restriction fragments. These findings demonstrated that environmental factors such as wetland plants and NH4+-N and NO3−-N concentrations had effects on the distri bution of microbial ammonia oxidizers and denitrifiers. Therefore, the responsible development of functional microbial communities could contribute to efficient N removal in the ICW.