Nitrogen removal by using sulfur-based carriers: a comparison of configurations for the denitrification process

To enhance the nitrogen removal efficiency from wastewater, elemental sulfur-based carriers were utilized to create the occurrence of the autotrophic denitrification (ADN) process. Three processes including sole heterotrophic denitrification (HDN), simultaneous heterotrophic and ADN (mixotrophic denitrification (MDN)), sequential heterotrophic and ADN were evaluated to compare the nitrogen removal performance in this study. The total nitrogen removal efficiency was 43% +/- 2% for the HDN due to the low C/N ratio of 2.8, and it was increased upto 56% +/- 2% for the MDN, and the highest removal efficiency was 93% +/- 1% for the sequential process. The ratios of sulfate generated to nitrate removed were 1.35 +/- 0.15, 3.46 +/- 0.14 mg SO42-/mg NO3--N for the mixotrophic and sequential denitrification processes, respectively, and lower than the theoretical ratio (7.54 mg SO42-/mg NO3--N). The chemical oxygen demand (COD) and total phosphorus (TP) removal efficiencies were obtained at 98% +/- 1%, 37% +/- 4%, and similar for three processes. The sulfur-based carriers can enhance the nitrogen removal without any adverse effect on COD and TP treatment.