Hybrid process of partial nitritation/anammox, solid-phase denitrification, and induced calcium phosphate crystallization for nitrogen removal and phosphorus recovery from high-strength sewage sludge drying wastewater

To achieve efficient nitrogen removal and phosphorus recovery from high-strength sewage sludge drying wastewater, a hybrid process integrating partial nitritation/anammox (PN/A), solid-phase denitrification (SPD), and induced calcium phosphate (Ca-P) crystallization was developed in this study. Through anaerobic pretreatment and a stepwise increase in the influent proportion of real wastewater, the PN/A-SPD systems achieved a total inorganic nitrogen removal efficiency of 93.40 ± 3.76 %. Metagenomic sequencing analysis indicated that ammonium-oxidizing bacteria (Nitrosomonas, relative abundance of 14.60 %) and anammox bacteria (primarily Candidatus Kuenenia, 8.77 %) were the dominant taxa involved in the tricarboxylic acid cycle and nitrogen metabolic pathways within the PN/A granules. In contrast, hydrolytic bacteria and denitrifiers, such as Anaerolinea, Rhodocyclaceae, Thauera, primarily contributed to the hydrolysis of solid carbon sources and heterotrophic denitrification within SPD biofilms. Furthermore, a phosphorus recovery efficiency of 94.47 ± 0.78 % was attained through induced Ca-P crystallization in a cement-based materials (CMs) packed column, where CMs served as phosphate adsorbents and seed nuclei. Needle-like hydroxyapatite and amorphous calcium phosphate were obtained from the surface of the CM particles. Compared to conventional activated sludge methods, the hybrid process demonstrated significantly lower energy and chemical consumption, lower carbon emission intensity, and reduced operational costs. These findings elucidate the integration mechanism among various functional units and provide feasible low-carbon strategies for treating nutrient-rich wastewater.