Nanobubble aeration accelerates manure wastewater sanitisation and enhances nitrogen retention while reduces...

Manure wastewater is an organic effluent rich in nitrogen and is often regarded as a valuable recycled nutrient source for crop production; however, it also contains high concentrations of organic pollutants and pathogenic microorganisms, and inadequate treatment can lead to serious environmental and public health risks. Nanobubbles (NBs) aeration is an emerging high-efficiency gas-liquid mass-transfer technology, but its role in nitrogen conservation and hygienic stabilisation of nutrient-rich manure wastewater remains unclear. Here, a 180-day experiment with piggery wastewater compared four NBs and conventional aeration regimes against natural storage. We quantified sanitisation performance, nitrogen transformation, greenhouse-gas emissions, microbial communities and virulence factors, and determined oxygen transfer rate (OTR), oxygen transfer efficiency (OTE) and volumetric mass-transfer coefficient (kLa) under identical airflow. NBs aeration markedly increased dissolved oxygen and ·OH generation, thereby enhancing COD, BOD₅ and Escherichia coliremoval and shortening the time to reach hygienic standards by 60 and 150 days compared with conventional aeration and natural storage, respectively.Although TN decreased in all treatments, the shorter sanitisation period under NBs aeration led to higher residual TN at compliance. The TN loss rate was 13.96% and 15.39% lower than under CA and CK, and cumulative N₂O emissions were 30.21% lower than under conventional aeration. Network and metagenomic analyses showed that NBs aeration reshaped bacterial, fungal and archaeal communities, weakened virulence-factor connectivity, and strengthened the coupling between nitrogen-cycling microbes and gaseous nitrogen pathways. Quantification of OTR, OTE and kLa demonstrated that these benefits arise from the intrinsic mass-transfer properties of nanobubbles rather than an increased oxygen supply rate. Overall, this work provides new mechanistic insight and engineering evidence that NBs aeration can simultaneously accelerate manure wastewater sanitisation and improve nitrogen management for subsequent fertiliser reuse.