Impact of High Salinity on Specific Oxygen Uptake, Nitrification and Denitrification Rates of Activated Sludge

The effects of high salinity on the fresh culture and the acclimated culture were investigated by monitoring specific oxygen uptake rate (SOUR), specific nitrification rate (SNR) and specific denitrification rate (SDNR). It was found that the SOUR of the fresh culture decreased from 19.36 to 5.83 mg O₂ /g MLVSS *h when the NaCl concentration was raised from 0 g/L to 30 g/L. The SOURs of the acclimated culture were higher than those of fresh culture due to the adaptation of the carbon-oxidizing bacteria after long periods of exposure to high salt contents. The nitrification bacteria were sensitive to high salinity than the carbon-oxidizing bacteria. When the NaCl content was increased from 0 to 10 g/L, the SNR of the fresh culture dropped sharply from 1.99 to 0.27 mg NH₄ ⁺-N /g MLVSS ldr h. During the period of acclimation, the SNR of the acclimated culture increased gradually and maintained about 2 mg NH₄ ⁺-N /g MLVSS ldr h at high salt contents of 10~35 g/L. Compared with the SNR, the SDNR of the fresh culture decreased more slowly with the elevated NaCl concentration, which revealed that the denitrifiers possessed a better salt tolerance than the nitrifiers. The SDNRs of the acclimated culture were about 10~16 mg NO₃ ^--N/g MLVSS ldr h at high salt contents of 10~35 g/L. With an adequate acclimation period and slowly increased salt content, the heterotrophic carbon bacteria, nitrifiers and denitrifiers could adapt themselves to high salt environment.