## 5 Conclusions  
Industrially relevant and state-of-the-art \"nanobubble-engineering\" metrics have been measured for a variety of commercial NB generators to a level of scientific and instrumental rigour applied very rarely--at least regarding what has been published in the open scientific literature. Although the water-flow NB generators were run in recirculation mode for 4 min, further work can certainly be conducted in single-pass mode to study \"virgin\" NB generation only. Given that the Stokes' Law \"buoyancy lifetime\" of NBs is expected to be much longer than their own internal (meta)stability [1; 2; 3; 9], the establishment of NB decay dynamics is particularly important--which the present study has accomplished.  
In any event, it was found that the electric-field approach to NB generation surpasses traditional mechanical approaches for clean-water NB generation, especially when considering the energy running cost. In particular, more passive electric-field approaches are very operationally attractive for NB generation, where water and gas flow can be handled at little to no cost to the end operator, and/or submersible NB generators can be deployed, allowing for the use of photovoltaic approaches (with backup batteries for night-time and \"low-sun\" scenarios and air-/CO\({}_{2}\)-pumping paraphenralia).  
Electric-field approaches are expected to be even greater in superiority to mechanical-generation approaches for wastewater treatment, where porous-membrane blockages become an insurmountable problem--never mind the impractically high operating energy cost.  
The present study has also called into question the level of bubble generation that is actually on the nanoscale in mechanically based commercially available generators that putatively produce NBs [42]. It has also sought to challenge the oft-prevailing industrial mindset of the (traditionally) dissolved gas level being characteristic of the effectiveness, or otherwise, of NB generation. Other metrics in water following fine-bubble generation, such as ORP and the relaxation thereof, or the time-resolved trajectory of DO (as opposed to the absolute value thereof in the immediate aftermath of fine-bubble generation) are more relevant to (putative) NB generation per se: hydrodynamically effective macrobubble generation can, and does, boost dissolved gas levels temporarily, for periods of tens of minutes until Stokes' Law dissipation (and/or chemical/biological gas demand) serves to reduce that. Therefore, actual and would-be NB-generator operators would do well to take note of these \"cautionary tales\" in their operational assessment of the effectiveness of their nano-/ fine-bubble-generation activities.  
The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app14177636/s1](https://www.mdpi.com/article/10.3390/app14177636/s1)]([https://www.mdpi.com/article/10.3390/app14177636/s1](https://www.mdpi.com/article/10.3390/app14177636/s1)), Figure S1: (**a**) Photovoltaic-powered submersible AquaB NB generator on a float with a battery and DC-fed air pump at ~60 lpm air (STP); (**b**) ~2500 m\({}^{3}\) of cyanobacteria-laden water in a 1.5 m-deep lake at average temperatures of 27-35 deg C, with mid-afternoon byocyanin Relative Fluorescence Unit (RFU) levels of 30-40, before an AquaB submersible unit was deployed, with some-based solar (and battery) or mains electricity as an option, as well as \"floating PV\" (FPV) as in panel \(a\); (**c**) Cyanobacteria eradication and suppression of eutrophication in the formerly benthic zone 7 days later.  
This research was funded by European Innovation Council, No. 190166658.  
Not applicable.  
The original contributions presented in the study are included in the article/Supplementary Materials, further inquiries can be directed to the corresponding author.  
The author declares no conflict of interest.