Elucidating the stimulatory and inhibitory effects of dissolved sulfide on sulfur-oxidizing bacteria (SOB) driven autotrophic denitrification.

Autotrophic denitrification has been widely studied for odor mitigation, corrosion control and nitrogen removal in recent years. This paper examines the response of sulfur-oxidizing bacteria (SOB) driven autotrophic denitrification under short-term stress of dissolved sulfide. A series of batch tests were conducted to investigate the effect of different sulfide concentrations (0-1600 mg-total dissolved sulfide (TDS)/L) on autotrophic denitrification and sulfide oxidation by SOB-enriched sludge. Our results show that autotrophic denitrification (NO3- to N2) was stimulated up to 200 mg-TDS/L with a maximum denitrification rate of 9.4 mg-N/g-volatile suspended solids (VSS)/h, and the nitrite reduction was a rate limiting step. When sulfide concentration was higher than 200 mg-TDS/L, it inhibited nitrate reductase, and nitrate reduction became the rate limiting step according to Edwards and Aiba inhibition models. Sulfide oxidation, however, was not inhibited and the maximum rate of 100.3 mg-TDS/g-VSS/h was obtained at sulfide concentration of 1000 mg-TDS/L. It is important to point out that the transient inhibition on autotrophic denitrification caused by high sulfide stress was resilient and non-lethal with no significant changes in cell viability even under sulfide concentration of 1000 mg-TDS/L. This study reveals the stimulatory and inhibitory effects of dissolved sulfide on SOB driven autotrophic denitrification and its possible underlying mechanism with discussion on engineering implications.