The novel Dirammox process for advanced nitrogen removal from high COD content and ammonium-rich wastewater

Abstract

Direct ammonia oxidation (Dirammox) is a novel inorganic nitrogen metabolism pathway identified in the genus Alcaligenes, which could convert ammonia to N₂ under aerobic conditions. With the remarkable nitrogen removal capabilities of this pathway, the heterotrophic genus Alcaligenes has considerable potential to efficiently and simultaneously remove nitrogen and organic matter from high chemical oxygen demand (COD) content and ammonium-rich wastewater. A novel lab-scale continuous-flow process termed “Dirammox membrane bio-reactor” (DMBR) was run over 9 months to test its possibility and efficiency for treating artificial ammonium-rich wastewater. There was stable performance, achieving an average ammonia removal (AR) of 95.4 %, total nitrogen removal (TNR) of 88.1 %, and COD removal of 95.0 %, with influent NH₄⁺-N concentrations up to 600 mg/L and COD of 7800 mg/L. Dirammox bacteria dominated the functional community with a relative abundance of 5.70 %. The total denitrifying bacteria was only 0.13 %. Nitrifying bacteria were not detected. The relative abundance of denitrification and ammonia oxidation genes (amoA, hao) was low. The copy number of dnfA was 7.59 × 10⁹/mg SS (dry), exceeding nirS [2.23 × 10⁴/mg SS (dry)]. Aerobic denitrification was inactive in the activated sludge. The Dirammox pathway removed ammonia and total nitrogen (TN), but not those employed in traditional nitrogen removal techniques. In summary, the Dirammox process efficiently removes organic matter and TN while preventing harmful nitrogen compound formation, offering a novel, sustainable, and more efficient solution for treating high COD content and ammonium-rich wastewater.