Enhanced Simultaneous Nitrogen and Phosphorus Removal Performance by Anammox-HAP Symbiotic Granules in the Attached Film Expanded Bed Reactor

Dissolved nitrogen and phosphorus compounds are responsible for eutrophication and usually are treated by separate processes in wastewater treatment plants. In this study, the simultaneous, long-term, stable removal of phosphorus and nitrogen was achieved in a high-loading anammox attached film expanded bed (AAFEB) reactor. As an energy-saving and high-efficiency biological process, the anammox reaction performed stable and high nitrogen removal. In addition, the chemical environment and hydrodynamic conditions of the AAFEB system, as well as the microenvironment of the anammox granules, induced the crystallization of hydroxyapatite (HAP). As an inorganic carrier of anammox biofilms, HAP enhanced the settling velocity and shear strength of the anammox granules and thus promoted the operational stability of the AAFEB reactor. In the coupled anammox HAP system, the nitrogen removal rate reached 44.8 g fo N/(L/day), with a stable phosphorus removal rate of 71.61 +/- 6.82%. The results indicated that the coupled anammox HAP system enhanced the nitrogen removal performance and provided a possible phosphorus recovery pathway through biomineralization processes.