Effects of pH and seasonal temperature variation on simultaneous partial nitrification and anammox in free-water surface wetlands

Design considerations to enhance simultaneous partial nitrification and anammox in constructed wetlands are largely unknown. This study examined the effects of pH and seasonal temperature variation on simultaneous partial nitrification and anammox in two free-water surface wetlands. In order to enhance partial nitrification and inhibit nitrite oxidation, furnace slag was placed on the rooting substrate to maintain different pH levels in the wetland water. The wetlands were batch operated for dairy wastewater treatment under oxygen-limited conditions at a cycle time of 7 d. Fluorescence in situ hybridization analysis found that aerobic ammonium oxidizing bacteria and anammox bacteria accounted for 42–73% of the bacterial populations in the wetlands, which was the highest relative abundance of ammonium oxidizing and anammox bacteria in constructed wetlands enhancing simultaneous partial nitrification and anammox. The two wetlands removed total inorganic nitrogen efficiently, 3.36–3.38 g/m2/d in the warm season with water temperatures at 18.9–24.9 °C and 1.09–1.50 g/m2/d in the cool season at 13.8–18.9 °C. Plant uptake contributed 2–45% to the total inorganic nitrogen removal in the growing season. A seasonal temperature variation of more than 6 °C would affect simultaneous partial nitrification and anammox significantly. Significant pH effects were identified only when the temperatures were below 18.9 °C. Anammox was the limiting stage of simultaneous partial nitrification and anammox in the wetlands. Water pH should be controlled along with influent ammonium concentration and temperature to avoid toxicity of free ammonia to anammox bacteria.

► Simultaneous partial nitrification and anammox was enhanced in free-water surface wetlands.
► Anammox bacteria accounted for approximately 18–38% of bacteria.
► Partial nitrification–anammox was significantly affected by a temperature variation of >6 °C.
► Partial nitrification–anammox was significantly affected by pH only at temperatures <19 °C.