Autotrophic denitrification with elemental sulphur in small-scale wastewater treatment facilities

An autotrophic denitrification process with elemental sulphur to achieve a high quality effluent with a low concentration of total N was tested at lab oratory scale. Two types of wastewater were tested during a period of 10 mo nths. One was a multiple household wastewater obtained from a municipal was tewater treatment plant and the other was a single household wastewater col lected from a family. The wastewaters were first treated by primary sedimen tation, followed by nitrifying trickling filtration. The nitrified effluent s from the trickling filter were further denitrified in an autotrophic deni trification stage. The autotrophic denitrifying reactor was filled with a m ixture of elemental sulphur powder and small pieces of limestone. Sulphur w as 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 oxidiza ble nitrogen (TON) was removed from the multiple household wastewater and 7 5 % 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 eff iciency and the short hydraulic retention time, other advantages were also noted such as no specific need for inoculum, rapid start up, a wide tempera ture range for application and low technical labour requirement. Hence,auto trophic denitrification offers interesting potential for removing surplus n itrate from nitrified domestic wastewater particularly in small-scale waste water treatment facilities.