Effects of seasonal temperature variation on nitrogen removal from a tidal flow constructed wetland system with CANON process

Abstract

We investigated the effects of seasonal temperature variation on the treatment perfor-mance and underlying mechanisms of nitrogen transformation in a tidal flow constructed wetland (TFCW) with the complete autotrophic nitrogen removal over nitrite (CANON) process. Different temperatures resulted in periodical variations in nitrogen transformation pathways and removal performance of the TFCW with CANON process, which was mainly due to the changes of dominant bacterial communities for nitrogen removal in the system. When temperature was higher than 20.0 ℃, nitrogen transformation and associated microbial characteristics in the TFCW were significantly affected, and the CANON process remained to be the principal pathway for nitrogen removal. The abundance and activity of anammox bacteria experienced different degrees of reduction when temperature dropped below 20.0 ℃. At the temperature of 9.3-20.0 ℃, the proliferation and increased activities of nitrite oxidizing bacteria (NOB) made the nitrification/denitrification process instead of the CANON process became the primary total nitrogen (TN) removal route in the TFCW, and the TN removal efficiency of the system declined to 34.8%±13.0%. Under the temperature range of 2.2-9.0 ℃, anammox bacteria, which was inhibited at the low temperatures, presented competitive advantage in comparison with NOB and denitrifiers, resulting that nitrogen removal in the TFCW relied on the CANON process again. Correspondingly, nitrogen removal rate of the system was 54.8%±4.8%. This study was conductive to the optimization of the TFCW with CANON process, as well as its engineering application.