Characterization and tuning dollops in potable water

Calcium carbonate (CaCO₃) nucleation and scaling present challenges in industrial and environmental contexts, especially in potable water systems, where mineral scaling affects infrastructure and water quality. The traditional understanding of CaCO₃ nucleation has evolved to include non-classical pathways, including prenucleation clusters and dynamically ordered liquid-like oxyanion polymers (DOLLOPs). This research aimed to characterize DOLLOPs in potable water to mitigate scaling, but it unexpectedly shifted focus to intrinsic nanobubbles found in alkaline solutions.

The research revealed that intrinsic CO₂ nanobubbles naturally form in alkaline aqueous solutions without external generation. Advanced techniques, such as Field-Flow Fractionation combined with Multi-Angle Light Scattering (FFF-MALS) and Zeta Nanoparticle Tracking Analysis (Z-NTA), characterized these nanobubbles in terms of size (approximately 100 nm in diameter), density, and zeta potential (negative charge). These nanobubbles are stable entities inherent to alkaline environments.

Investigations into the influence of magnetic fields on nanobubble formation revealed that rotating magnetic fields significantly enhanced charged nanobubble formation, increasing their density and negative charge while impacting size distribution. This suggests that magnetic fields can control nanobubble populations in aqueous systems.

The role of intrinsic nanobubbles in CaCO₃ formation was examined, revealing that charged nanobubbles inhibit nucleation by stabilizing the dense liquid calcium carbonate phase, preventing aggregation and delay in solid amorphous calcium carbonate (ACC) formation. Magnetically generated nanobubbles had a stronger effect, suggesting they influence the non-classical nucleation pathway by stabilizing intermediate states and delaying solid ACC formation.

Additionally, Asymmetric Flow Field-Flow Fractionation coupled with Multi-Angle Light Scattering and Inductively Coupled Plasma Mass Spectrometry (AF4-MALS-ICP-MS) detected nanoparticles in drinking water samples, indicating potential DOLLOPs. Metals like magnesium were associated with small particles (1.5 to 10 nm), indicative of prenucleation clusters or DOLLOPs.
The findings emphasize the crucial role of intrinsic nanobubbles in CaCO₃ nucleation and scaling in potable water systems. Recognizing nanobubbles as inherent components offers a fresh perspective on mineral scaling, providing novel approaches to manipulating CaCO₃ nucleation and scaling control in water treatment technologies.