Nitrogen removal performance using anaerobic ammonium oxidation at low temperatures

An anaerobic ammonium oxidation (anammox) process for ammonia-rich wastewater treatment has not been reported at temperatures below 15 °C. This study used a gel carrier with entrapped anammox bacteria to obtain a stable nitrogen removal performance at low temperatures. In a continuous feeding test, a high nitrogen conversion rate (6.2 kg N m^-3 day^-1) was confirmed at 32 °C. Nitrogen removal activity decreased gradually with decreasing operation temperature; however, it still occurred at 6 °C. Nitrogen conversion rates at 22 and 6.3 °C were 2.8 and 0.36 kg N m ^-3 day^-1, respectively. Moreover, the stability of anammox activity below 20 °C was confirmed for more than 130 days. In batch experiments, anammox gel carriers were characterized with respect to temperature. The optimum temperature for anammox bacteria was found to be 37 °C. Furthermore, it was clear that the temperature dependence changed at about 28 °C. The apparent activation energy in the temperature range from 22 to 28 °C was calculated as 93 kJ mol^-1, and that in the range from 28 to 37 °C was 33 kJ mol^-1. This value agrees with the result of a continuous feeding test (94 kJ mol^-1, between 6 and 22 °C). The nitrogen removal performance demonstrated at the low temperatures used in this study will open the door for the application of anammox processes to many types of industrial wastewater treatment.