Research on the influence mechanism of low-temperature storage on nitrifying bacteria

To develop a more cost-effective nitrogen removal strategy, this study investigated the impact of low-temperature storage methods on nitrifying bacterial activity. Sludge was stored under laboratory-scale static batch conditions in three media: (1) distilled water, (2) nutrient solution, and (3) nutrient solution supplemented with hydroxylamine (NH₂OH). Ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) activity, sludge properties, and microbial characteristics were examined. Results revealed that all storage methods inhibited both AOB and NOB activity. Notably, nutrient solution storage demonstrated the most significant effect: it suppressed NOB activity by 86.6% and reduced its relative abundance by 20%, while maintaining high extracellular polymeric substance content (43.5 mg/g VSS) and AOB relative abundance (0.18%). This method substantially shortened the required storage duration (from 8 months to 60 days) and better preserved AOB activity and sludge stability. Metagenomic analysis indicated strong inhibition of the NOB functional gene nitrite oxidoreductase across all methods, while nutrient solution storage specifically elevated the abundance of the AMO gene. Although NH₂OH supplementation exhibited inhibitory effects on microorganisms, the concurrent addition of nutrient solution effectively mitigated this impact. Consequently, sludge properties and functional microbiota abundance showed no significant difference between the NH₂OH-supplemented nutrient solution method and distilled water storage.