The effect of low temperatures on ammonia removal in a laboratory-scale constructed wetland

The effect of low temperatures on ammonia removal in constructed Wetlands was studied by running a synthetic wastewater through a model, laboratory-scale gravel-filled constructed wetland (in which no plants were grown). The wetland was operated at temperatures of 5, 11.5, 15, and 23 °C in an environmentally controlled chamber. An influent ammonia concentration of 45 mg/L as nitrogen was used to simulate typical domestic wastewater. For temperatures of 5, 11.5, 15, and 23 °C, the wetland model achieved ammonia removal and nitrification of 45, 44, 56, and 65%, respectively. Thus, over the 18 °C temperature range ammonia-nitrogen removal and nitrification rates varied only 20%. There was a net decrease in nitrogen as water passed through the wetland; this could be the result of cell growth or denitrification. Measurements were taken at the inlet, outlet, and four additional locations along the length of the reactor. Measurements were also taken at three different depths. Along the length of the reactor, nearly all nitrification was achieved in the first half of the reactor, then stopped because of low dissolved oxygen concentrations. Nitrification occurred slightly faster at the top of the reactor than at the bottom.