Pilot and full scale applications of sulfur-based autotrophic denitrification process for nitrate removal from activated sludge process effluent

• Autotrophic denitrification process was used for wastewater treatment.
• Sulfur-based denitrification process was optimized in pilot scale reactors.
• Full scale application of sulfur-based denitrification process was illustrated.
• Process was effective up to loading of 10 mg −NO3NO3−–N/(L.h).
• Alkalinity may limit the process at high loadings.

Sulfur-based autotrophic denitrification of nitrified activated sludge process effluent was studied in pilot and full scale column bioreactors. Three identical pilot scale column bioreactors packed with varying sulfur/lime-stone ratios (1/1–3/1) were setup in a local wastewater treatment plant and the performances were compared under varying loading conditions for long-term operation. Complete denitrification was obtained in all pilot bioreactors even at nitrate loading of 10 mg −NO3NO3−–N/(L.h). When the temperature decreased to 10 °C during the winter time at loading of 18 mg −NO3NO3−–N/(L.h), denitrification efficiency decreased to 60–70% and the bioreactor with S/L ratio of 1/1 gave slightly better performance. A full scale sulfur-based autotrophic denitrification process with a S/L ratio of 1/1 was set up for the denitrification of an activated sludge process effluent with a flow rate of 40 m3/d. Almost complete denitrification was attained with a nitrate loading rate of 6.25 mg −NO3NO3−–N/(L.h).