Efficient nitrogen removal from acrylic fiber wastewater achieved by the partial denitrification-anammox granule process through gradient-driven microbial remodeling

• PDA granules is efficiently compatible with acrylic fiber wastewater via gradient-driven strategy. • Nitrogen removal efficiency is achieved 90.4% under authentic wastewater conditions. • Partial denitrification sustains sufficient nitrite substrate despite increasing stress. • Elevated hydrophobic proteins enhance the granular aggregation and integrity. • Thauera periphery ensured the survival and activity of inner anammox bacteria. The partial denitrification-anammox (PDA) process holds promise for nitrogen removal in acrylic fiber wastewater (AFW), yet its application stability is challenged by the sensitivity of anammox bacteria. This study applied a gradient-driven microbial remodeling strategy to the partial denitrification-anammox (PDA) granule process, incrementally increasing the acrylic fiber wastewater (AFW) influent ratio (30%, 60%, 100% v/v) to steer microbial adjustments. The engineered PDA granules achieved 90.4% ± 2.4% total nitrogen removal with more than 85% via the anammox pathway, under a carbon-to-nitrogen ratio of 1.5 and a hydraulic retention time of 10.7h. A critical outcome was the establishment of a highly robust partial denitrification (PD), consistently maintaining a nitrite accumulation ratio of over 70% to ensure sufficient nitrite substrate for anammox. Furthermore, the production of protein-rich extracellular polymeric substances (EPS) increased markedly through positive microbe responses, enhancing the granular integrity and stability. Crucially, an adaptively self-organized, stratified granule architecture emerged: Thauera (52.6%) in the outer layer drove the PD process and EPS formation, creating a spatially sheltered core where Candidatus Brocadia (1.6%) thrived. This work demonstrates that leveraging the inherent AFW inhibition as a gradient-driven force is a viable strategy to remodel microbial structure and function, securing the efficient anammox performance, which provides valuable insights for sustainable nitrogen management in recalcitrant wastewater.