Effect of salinity on the denitrification of the sulfur-based autotrophic denitrification system

This study investigated the effect of gradual salt concentration increases on the nitrogen removal performance from a sulfur-based autotrophic denitrification (SAD) process. A continuous operation reactor was used to study the adaptability of sulfur-based autotrophic denitrifying bacteria to changes in salinity. The study focused specifically on the effects of SO42- and Cl- on the activity of SAD bacteria. When the concentration of SO42- was 0-4 g/L, NO3--N was removed at more than 97%. When the concentration of SO42- increased to 15 g/L, the removal of NO3--N decreased to 51%. When the concentration of NaCl was 0-30 g/L, the removal rate of NO3--N was all greater than 97%. When the concentration of NaCl increased to 80 g/L, the removal rate of NO3--N decreased to 34.6%. When the NaCl concentration was 50 g/L, the removal rate of NO3--N decreased to 80.59% at first, and the removal rate of NO3--N recovered to 98% after 16 days of operation. When the NaCl concentration increased to 80 g/L, the NO3--N removal rate decreased to 50%, and the reactor still could not recover its performance after longterm operation. The growth of halophilic heterotrophic bacteria with the increase of NaCl concentration leads to an increase in the abundance of Proteobacteria. The higher concentration of Cl- seriously inhibits the growth of Sulfurimonas and Thiobacillus, decreasing the effectiveness of bacteria to remove nitrogen.