Autotrophic Denitrification with Elemental Sulphur in Small-Scale Wastewater Treatment Facilities

Abstract

An autotrophic denitrification process with elemental sulphur to achieve a high quality effluent with a low concentration of total N was tested at laboratory scale. Two types of wastewater were tested during a period of 10 months. One was a multiple household wastewater obtained from a municipal wastewater treatment plant and the other was a single household wastewater collected from a family. The wastewaters were first treated by primary sedimentation, followed by nitrifying trickling filtration. The nitrified effluents from the trickling filter were further denitrified in an autotrophic denitrification stage. The autotrophic denitrifying reactor was filled with a mixture of elemental sulphur powder and small pieces of limestone. Sulphur was used as an electron donor and CaCO₃ in the limestone served as pH buffer. With a hydraulic retention time of 2–3 hours, up to 86 % of total oxidizable nitrogen (TON) was removed from the multiple household wastewater and 75 % from the single household wastewater. The total N concentration in the final effluents was 3 mg l⁻¹ for the multiple household wastewater and 17 mg l⁻¹ for the single household wastewater. Besides the high removal efficiency and the short hydraulic retention time, other advantages were also noted such as no specific need for inoculum, rapid start up, a wide temperature range for application and low technical labour requirement. Hence, autotrophic denitrification offers interesting potential for removing surplus nitrate from nitrified domestic wastewater particularly in small-scale wastewater treatment facilities.