Application of micro- and nanosized bubbles for the separation of phosphorus nanoparticles released from sediments

We applied air bubbles ranging in size from micrometers to nanometers to collect phosphorus (P) at nanoscale sizes for the purpose of studying the potential for P removal in aqueous environments. The P removal efficiency of microbubbles (MBs) and micro-nanobubbles (MNBs) was systematically evaluated using nano-sized P particles (PNPs) of different sizes. The MBs alone showed only limited removal efficiency, with efficiency decreasing as the PNPs' size decreased. Conversely, with the integration of NBs, the P particle removal efficiency was enhanced, reaching 34.09% for total P and 18.91% for soluble P (PO₄-P) in the P particle size range of 0–0.45 μm after 5 min of flotation. This result is also consistent with the theoretical separation efficiency, calculated based on the extended Derjaguin–Landau–Verwey–Overbeek (EDLVO) theory of total interaction force, which predicts an energy barrier at approximately 2 nm. This improvement is attributed to NBs acting as bridging agents, promoting the adhesion of PNPs to MBs. These results suggest that MBs and NBs, when combined, can improve flotation efficiency; however, they need to be integrated with appropriate pretreatment methods to achieve a higher overall P removal efficiency.