Influence of temperature fluctuations on one-stage deammonification systems in northern cold region

Abstract

Cold and fluctuant temperatures are still a bottleneck for the application of one-stage deammonification in mainstream anammox (anaerobic ammonium oxidation). In this study, to simulate the practical but critical operational condition under rapidly fluctuant temperatures between April and May in cold northern area, two deammonification reactors with anammox granular sludge and nitritation flocculent sludge were tested under the cold shock with temperature fluctuations (11–18 °C). Under the controlled temperature (32 °C), good performances were obtained in both reactors. However, after the cold shock (ca. 13 °C), both reactors deteriorated similarly. The ammonia removal efficiencies decreased by half, while total nitrogen (TN) removal efficiencies decreased by two thirds. Nitrite accumulated in both reactors, while nitrate production was not disturbed although its contributions from nitrite oxidizing bacteria (NOB) increased. In the stage with increasing wastewater temperatures (17.5 ± 2.2 °C), several operational conditions were tested to recover the performances, including limited dissolved oxygen, long hydraulic retention time (HRT), high nitrogen loading with elevated pH, and low NH₄⁺–N (60 mg/L), which did not significantly improve the performances, while the phenomena of heterotrophic nitrate reduction dramatically improved the nitrogen removal performances under limited aeration. During the cold temperature shock, insufficient anammox activity, and nitrate overproduction were the main problems.