A new pattern of the partial nitrification and Anammox immobilized gel beads: core-shell embedded carrier

Single-stage partial nitrification and Anammox (PN/A) is an efficient and energy-saving denitrification process for wastewater. However, its application is limited by the growth conditions of microorganisms. Therefore, we improved the PN/A by developing a novel core−shell embedded carrier. With Anammox gel as the core and Ammonia-oxidizing bacteria gel as the shell, these beads can achieve dissolved oxygen partitioning and provide a suitable environment for the growth of different bacteria. On this basis, the influence of the shape of core−shell embedded gel on nitrogen removal performance was systematically studied, and the internal morphology and pore size of gel beads were characterized. The results showed that the nitrogen removal efficiency of spherical and square gels was increased by 33.70% and 13.47%, respectively, in the batch test. Fluorescence in situ hybridization confirmed the stratified growth of ammonia-oxidizing bacteria and Anammox in carriers, and the relative abundance value of the two bacteria were 1.25:1 and 1.43:1, respectively. Although the mechanical strength of square gel beads is slightly higher than that of spherical, spherical gel is considered the most suitable gel shape due to its small pore size and poor pore connectivity, which ensures the matching of internal Anammox and external PN reaction. In the long-term experiment, the core−shell embedded beads still had the design characteristics, and the TN removal efficiency was increased by 36.25% despite occasional oxygen excess.