Facultative autotrophic denitrifiers in denitrifying sulfide removal granules

The denitrifying sulfide removal (DSR) process applied autotrophic and heterotrophic denitrification pathways to achieve simultaneous conversion of nitrate to N2, sulfide to elementary sulfur, and organic substances to CO2. However, autotrophic denitrifiers and heterotrophic denitrifiers have to grow at comparable rates so the long-term DSR stability can be maintained. This work assessed the autotrophic and heterotrophic denitrification activities by 16 isolates from anaerobic granules collected from a DSR-expanded granular sludge bed reactor. A group of strains with closest relatives as Pseudomonas sp. (89.9–98.3% similarity), Agrobacterium sp. (94.6% similarity) and Acinetobacter sp. (96.6% similarity) were identified with both autotrophic and heterotrophic denitrification capabilities. These facultative autotrophic denitrifiers can be applied as potential strains for lifting the limitation by balanced growth of two distinct bacterial groups in the DSR reactor.