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Impacts of sulfur source and temperature on sulfur-driven denitrification by pure and mixed cultures of Thiobacillus

Di Capua, Francesco, Ahoranta, Sarita H., Papirio, Stefano, Lens, Piet N.L., Esposito, Giovanni
Process biochemistry 2016 v.51 no.10 pp. 1576-1584
Thiobacillus denitrificans, Thiobacillus thioparus, activation energy, bioassays, denitrification, equations, mixed culture, nitrates, solubility, sulfur, temperature, thiosulfates
This study investigated the impacts of thiosulfate (S2O3²⁻) as well as chemically synthesized and biogenic elemental sulfur (S⁰) on the rates of sulfur-based denitrification in batch bioassays. The use of S2O3²⁻ resulted in the highest denitrification rate (52.5mg N-NO3⁻/L d), whereas up to 10 times slower nitrate (NO3⁻) removal was observed with S⁰. Biogenic S⁰ was tested for the first time as electron donor for chemolithotrophic denitrification, resulting in 1.7-fold faster NO3⁻ removal than that achieved with chemically synthesized S⁰. The effects of increasing concentrations of S2O3²⁻ and chemically synthesized S⁰ on denitrification were evaluated testing three different sulfur-to-nitrogen (S/N) molar ratios (1.8, 3.5 and 5.1) on a pure culture of Thiobacillus denitrificans and a mixotrophic enrichment dominated by Thiobacillus thioparus. S2O3²⁻ concentrations exceeding 2.2g/L inhibited the activity of T. denitrificans, whereas a stimulatory effect was observed on mixotrophic denitrification. The increase in S⁰ concentration slightly enhanced denitrification by both microbial cultures due to the low solubility of chemically synthesized S⁰. The temperature dependence of the thiosulfate-driven denitrification by T. denitrificans was investigated to further optimize the process and modeled by the Arrhenius equation with an apparent activation energy Ea of 76.6kJ/mol and a temperature coefficient Q10 of 3.0.