Effect of salinity on anammox nitrogen removal efficiency and sludge properties at low temperature

Anaerobic ammonium oxidation (Anammox) process is a new type of biological nitrogen removal technology that is highly efficient, consumes low energy, and is cost-effective. However, from a practical perspective, there are operational problems involved with the technology, due to its special low temperature environmental conditions. As such, the technology is currently a key research direction in the field of sewage control engineering. This study investigated the effect of salinity on the performance of the anammox process at the stress of a low temperature (15℃) and the role salinity has on extracellular polymeric substance (EPS) secretion and by extension, anammox activated sludge. The study tested the technology used to adjust and control salinity at a low temperature. The study found that at a low temperature of 15℃, low salinity can promote the nitrogen removal efficiency of anammox bacteria. Low salinity can also activate anammox bacteria activity. However, in contrast with low salt concentrations, high salt concentrations can inhibit anammox activity. When the temperature was 15℃ and the salinity was 4 g/L, the nitrogen removal efficiency of the reactor was 1.79 times higher than in the environment with unadjusted salinity at 15℃. At a low temperature, as salinity increased, the water binding capacity and flocculation capacity of sludge also increased. Salinity can promote the secretion of EPS and changes its composition. Under low temperature stress, the concentration of salt was less than 12 g/L, and the anammox activity improved. However, a high salinity level significantly inhibited anammox activity.