Autotrophic denitrification of nitrate and nitrite using thiosulfate as an electron donor

• Both nitrate and nitrite were removed by autotrophic denitrification using thiosulfate.
• Produced sulfate in nitrite denitrification was less than that in nitrate.
• pH and alkalinity during nitrate denitrification decreased but increased with nitrite.
• qmax and KS of nitrite was higher (1.5 and 1.1 times) than that of nitrate.
• Biomass yield for nitrate was relatively higher than that of nitrite.

This study was carried out to determine the possibility of autotrophic denitritation using thiosulfate as an electron donor, compare the kinetics of autotrophic denitrification and denitritation, and to study the effects of pH and sulfur/nitrogen (S/N) ratio on the denitrification rate of nitrite. Both nitrate and nitrite were removed by autotrophic denitrification using thiosulfate as an electron donor at concentrations up to 800 mg-N/L. Denitrification required a S/N ratio of 5.1 for complete denitrification, but denitritation was complete at a S/N ratio of 2.5, which indicated an electron donor cost savings of 50%. Also, pH during denitrification decreased but increased with nitrite, implying additional alkalinity savings. Finally, the highest specific substrate utilization rate of nitrite was slightly higher than that of nitrate reduction, and biomass yield for denitrification was relatively higher than that of denitritation, showing less sludge production and resulting in lower sludge handling costs.