Sustainability-oriented design of an air micro–nanobubble-assisted polishing system for Andrias davidianus aquaculture effluent

Intensive aquaculture generates nutrient-rich effluents that increase freshwater demand and pollutant export. This study evaluated an air micro–nanobubble-assisted three-pond/two-dam polishing and treated-outflow collection system for Chinese giant salamander (Andrias davidianus) effluent in Shanxi, China. The pilot was operated as a polishing and treated-water collection pathway. Monitoring from 5 June to 5 December 2024 covered summer-to-early-winter site-relevant stressors. Under routine flow conditions, the operational hydraulic residence time was approximately 3–4 d, and paired inlet–outlet observations showed consistent reductions in nutrients, organic matter, turbidity, and fecal coliform. Median outlet concentrations were 0.65 mg L⁻¹ for total nitrogen, 0.18 mg L⁻¹ for total phosphorus, 0.40 mg L⁻¹ for ammonia nitrogen, 14.11 mg L⁻¹ for chemical oxygen demand, and 9.80 NTU for turbidity; corresponding median removals were 37.0%, 44.9%, 35.3%, 46.2%, and 58.3%. Fecal coliform was reduced by 70.1%. Treated outflow was transferred to an external collection tank for verification and non-food irrigation, and photovoltaic generation offset 70.9% of monitored gross electricity demand. Outlet quality improved, but direct husbandry reuse was not demonstrated because dissolved oxygen remained insufficient and biological endpoints, complete pathogen-risk assessment, direct recirculation, and isolated MNB effects were not tested.