Ammonia-oxidizing bacterial community and nitrification rates in constructed wetlands treating swine wastewater

► The constructed wetlands were effective in NH4+, NO3−, and COD removal. ► The correlations between the ammonia-oxidizing bacteria and nitrification rate were investigated. ► The Shannon-Weaver diversity index did not correlate with nitrification rate. ► amoA gene copies in the influent of the continuous wetland cell (CI) were higher than of the marsh-pond-marsh wetland cell (MI). ► The phylogenetic analysis of ammonia-oxidizing bacteria was performed.