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

tThis study investigated the impacts of thiosulfate (S2O32−) as well as chemically synthesized and bio-genic elemental sulfur (S0) on the rates of sulfur-based denitrification in batch bioassays. The use ofS2O32−resulted in the highest denitrification rate (52.5 mg N-NO3−/L d), whereas up to 10 times slowernitrate (NO3−) removal was observed with S0. Biogenic S0was tested for the first time as electron donorfor chemolithotrophic denitrification, resulting in 1.7-fold faster NO3−removal than that achieved withchemically synthesized S0. The effects of increasing concentrations of S2O32−and chemically synthesizedS0on 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 byThiobacillus thioparus. S2O32−concentrations exceeding 2.2 g/L inhibited the activity of T. denitrificans,whereas a stimulatory effect was observed on mixotrophic denitrification. The increase in S0concentra-tion slightly enhanced denitrification by both microbial cultures due to the low solubility of chemicallysynthesized S0. The temperature dependence of the thiosulfate-driven denitrification by T. denitrificanswas investigated to further optimize the process and modeled by the Arrhenius equation with an apparentactivation energy Eaof 76.6 kJ/mol and a temperature coefficient Q10of 3.0.