Speci®c oxygen, ammonia, and nitrate uptake rates of a biological nutrient removal process treating elevated salinity wastewater

Anaerobic/anoxic/aerobic systems inoculated without and with NaCl acclimated cultures, i.e., Models A and B, respectively, were fed with a synthetic wastewater at various salinity levels. After achieving a steady state, the systems were shocked with 70 g/l NaCl for four consecutive days before returning to pre-shock conditions. At the steady-state, the speci®c oxygen uptake rates (SOURs) increased with an increase of sodium chloride concentration (from 5.40 to 9.72 mg O2/g mixed liquor suspended solids (MLSS)-h at 0±30 g/l NaCl for Model A and from 6.84 to 17.64 mg O2/g MLSS-h at 5±30 g/l NaCl for Model B). In contrast, the speci®c ammonia uptake rate (SAUR) and speci®c nitrate uptake rate (SNUR) decreased with increasing chloride concentration (from 4.76 to 2.14 mg NH3±N/g MLSS-h and 2.50 to 1.22 NO3±N/g MLSS-h, for Model A, and from 3.84 to 2.71 mg NH3±N/g MLSS-hr and 2.54 to 1.82 mg NO3±N/g MLSS-hr, for Model B). During the shocked period, the SOUR in most scenarios increased whereas the SAUR and SNUR tended to decrease. The impact of the chloride shock on nitri®ers was more obvious than on denitri ®ers; however, after a certain recovery period, the activities of both nitri®ers and denitri®ers in terms of SAUR and SNUR were approximately the same as those prior to shock.