Construction of an autotrophic nitrifying granular sludge partial nitritation system based on reaction rate

This study presented a strategy for rapid establishing partial nitritation using autotrophic nitrifying granular sludge (ANGS), offering a green and efficient solution for treating ionic rare earth mining wastewater, which is characterised by acidic pH, low organic content, and elevated ammonia nitrogen. Experiments were conducted in a sequencing batch reactor (SBR) inoculated with stored granules. By Day 8, the ANGS demonstrated excellent recovery of activity, with the nitrite accumulation rate (NAR) exceeding 90%. Through controlled aeration intensity, the ammonia oxidation rate and nitrite oxidation rate of the ANGS were leveraged to regulate aeration time. A NO₂^--N/NH₄⁺-N ratio of approximately 1.32 was firstly achieved by Day 25 when the nitrogen loading rate (NLR) was 0.24 kg/m³·d, and partial nitritation was also achieved by Days 41, 54, 70 and 85 respectively when the NLRs were 0.30, 0.36, 0.42, and 0.48 kg/m³·d. Ammonia oxidising bacteria (AOB) remained highly active, while nitrite oxidising bacteria (NOB) were effectively suppressed. By the conclusion of the experiment on Day 90, the dominant microbial communities in the reactor were Nitrosomonas (20.32%), Thauera (12.57%), and OLB8 (10.60%). Metagenomic analysis revealed a significant enhancement in the relative abundance and activity of amoC (encoding ammonia monooxygenase) and hao (encoding hydroxylamine oxidoreductase) in AOB. The calculated conversion costs for different NLRs per cycle were 4.646, 6.845, 8.901, 9.538 and 10.222 RMB/m³.