Augmentation of mixotrophic denitrification by using iron-rich desulfurized waste as a co-substrate in sulfur-ethanol-based denitrification

The scientific investigation of employing heterotrophic/autotrophic (mixotrophic) denitrification to address the issue of wastewater containing elevated levels of nitrate nitrogen (NO₃⁻-N) has garnered significant attention. This study utilized sulfur-based denitrification with iron-process (SDIP) supplemented with ethanol to enhance the heterotrophic denitrification. The iron compounds used in this study were obtained from treatment of acid mine drainage wastewater with calcium hydroxide Ca(OH)₂. The sludge thus formed contained a high quantity of iron compounds along with calcite deposits on its surface. The effectiveness of mixotrophic denitrification was found to be superior in reactors with iron supplementation as compared to the sulfur only reactor. Even at a very low C/N ratio, high concentration of nitrate can be removed through this novel combination. The SDIP system maintains the pH levels during the denitrification process, eliminating the need for additional alkalinity sources and thereby reducing operating costs. Furthermore, the SDIP system effectively eliminated the smell of hydrogen sulfide (H₂S) throughout its operation.