Partial nitrification and denitrification in a sequencing batch reactor treating high-salinity wastewater

Abstract

The effect of salinity on partial nitrification–denitrification (PND) and sludge activities was investigated in a sequencing batch reactor (SBR). During a 176-day long-term operation, influent salinity was increased from 5.0 to 41.9gNaCl/L. In the salt concentration range of 5 to 37.7g/L, the increase of salinity did not inhibit ammonium oxidation and nitrite denitrification, and high nitrite accumulation rate (NAR) (>92.6%), ammonium removal efficiency (>98.5%) and total nitrogen (TN) removal efficiency (>98.5%) could be recovered. In a typical cycle, almost complete partial nitrification occurred at aeration time less than 3.5h, and in the next anoxic phase, nitrite nitrogen was removed almost completely in 30min. Ammonium oxidation process was significantly inhibited when the salt concentration was increased to 41.9g/L, and ammonium and TN removal efficiencies dropped to 43.7% and 46.2%, respectively. Batch test of sludge activity revealed that ammonium oxidizing bacteria were stimulated obviously under the salinity of 9.0–25.1g/L, while nitrite oxidation was not observed in the salinity range studied. At the salinity of 9.0g/L, the ammonium oxidizing rate of the sludge from the SBR reached the maximum value and was twice as much as that of the seeding sludge. Compared to the seeding sludge, the sludge from the SBR at the salinity of 5.0–16.8g/L obtained higher nitrite and nitrate reduction activities. The present SBR is a promising process for efficient nitrogen removal in highly saline wastewaters by partial nitrification and denitrification.