Abundance and Diversity of Bacterial Nitrifi ers and Denitrifi ers and Their Functional Genes in Tannery Wastewater Treatment Plants Revealed by High-Throughput Sequencing

Tannery wastewater is characterized by high contents of nitrogen, organic compounds and salt ions [1],[2], and the complexity of the wastewater components can affect microbial nitrification/denitrification processes that have been frequently used for nitrogen removal in wastewater treatment plants (WWTPs). Nitrification, the biological oxidation of ammonium to nitrite and nitrate, is carried out in two sequential steps via several

phylogenetically distinct groups of microorganisms: ammonia-oxidizing archaea (AOA), ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) [3]. Denitrification consists of consecutive reactions including transformation of nitrate or nitrite into gaseous forms (N2 or N2O) by different groups of bacteria (nitrifiers and denitrifiers) [4].