Isolation and characterization of sulfur-utilizing denitrifiers from the sulfur-oxidizing denitrification process

Of 14 potential sulfur-oxidizing strains, Pseudomonas sp. B21 and Agrobacterium sp. B19 were considered as denitrifiers. Under aerobic conditions, with S0 as electron donor, maximum cell growth rates were 0.022 (B21) and 0.043 h(-1) (B19). Both grew optimally at pH 7.5 and 28 degrees C. When NO3-N was increased from 10 to 200 mg l(-1) the efficiency of nitrate removal of each strain gradually decreased, from 60 to 40%. Addition of suitable organic compounds (C/N < 4.2) increased the nitrate removal efficiencies of both strains, indicating their mixotrophic characters.