Dialysis-assisted control significantly enables stable long-term unaerated partial nitrification in a...

Source-separated hydrolyzed urine (SSHU), with high ammonium (NH₄⁺-N) concentration and low carbon-to-nitrogen ratio, presents a critical challenge for conventional biological treatment. This study developed an unaerated microalgal-bacterial consortium (MBC) integrating dialysis to achieve stable partial nitrification (PN) for SSHU treating. This system achieved 166-day stable PN (nitrite accumulation rate >85 %) through three mechanisms: (1) Dialysis and shorten hydraulic retention time (6 d to 2 d) maintained free ammonia (>2.87-4.56 mg/L) and in-situ free nitrous acid (>0.082 mg/L), selectively inhibiting nitrite-oxidizing bacteria (NOB). (2) Microalgae-derived dissolved oxygen (9.37-10.79 mg/L) supporting ammonia-oxidizing bacteria and bioavailable dissolved organic matter (COD: 200.83 mg/L) enhancing denitrifiers against NOB. (3) Specific light energy density (>0.030 kJ/mg VSS) sustained NOB suppression. Harvested biomass contained high-value fatty acids (0.47 mg/mg) and amino acids (0.42 mg/mg), suitable for biodiesel (C16-C20) and antioxidant production. This U-PNMBC system provides an energy-efficient solution for high NH₄⁺-N waste streams.