Stimulation of Nitritation and Changes in Nitrifying Bacterial Microflora in a DHS Reactor by Controlling Salinity

Abstract

The effect of salinity on nitritation in a Down-flow Hanging Sponge (DHS) reactor was evaluated through a long-term continuous experiment for 700 days. The DHS reactor was fed with artificial wastewater containing 100 mg-N·L^-1 ammonium nitrogen (HRT = 2 h, 20-25°C). The salinity of the influent was controlled by adding NaCl at concentrations of 5 to 18 g-Cl^-·L^-1. The effluent nitrite concentration increased with increasing of salinity, i.e., the nitrite concentration increased up to approximately 60% of the total nitrogen in the effluent at 18 g-Cl^-·L^-1. The nitrifying bacterial community in the DHS markedly changed at the species level. For example, the dominant nitrite-oxidizing bacteria changed from Nitrospira-sublineage I at 0 g-Cl^-·L^-1 to Nitrobacter spp. at 18 g-Cl^-·L^-1.