## 4 Results and Discussion
Turning to submersible NB generators, the AquaB generator (7) was powered by mains electricity for AC-DC, and the Acniti microStar (6) was placed above the water line, and 10 lpm (STP) of air was added via a low-power air pump (\(\sim\)15 W). Important results are summarised in Table 8.  
It is clear that the level of NB production, in terms of mass of NBs per unit power, is roughly \(\sim\)10 \(\times\) 20 = 200-times better for the electric-field approach, with about two-thirds of \begin{table}
\begin{tabular}{l c c} \hline \hline
**Type/Model** & **\% of Total Dissolved O\({}_{2}\)** & **\% of Incoming O\({}_{2}\)** \\ \hline \hline
1: Moleaer Kingfisher & 4.6 & 0.6 \\ \hline
2: Acniti Turbiti 727 & 5.6 & 0.8 \\ \hline
3V: AquaB In-line Tubular Pipe (Venturi) & 37 & 23 \\ \hline
3C: AquaB In-line Tubular Pipe (Air Comp.) & 40 & 28 \\ \hline
4V: AquaB Radial Vortex (Venturi) & 55 & 30 \\ \hline
4C: AquaB Radial Vortex (Air Comp.) & 58 & 34 \\ \hline
5: Anzai Porous Membrane & 4.8 & 0.9 \\ \hline
3V: AquaB In-line (Off-Grid, incl. P-drop) & 29 & 21 \\ \hline
3V: AquaB In-line (Off-Grid, excl. P-drop) & 29 & 21 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Oxygen NB mass as a percentage of total dissolved O\({}_{2}\) (i.e., DO boost + NB) and as % of incoming gas. \begin{table}
\begin{tabular}{l c} \hline \hline
**Type/Model** & \(\tau\) \\ \hline \hline
1: Moleaer Kingfisher & 1.4 \(\pm\) 0.25 \\ \hline
2: Acniti Turbiti 727 & 1.6 \(\pm\) 0.28 \\ \hline
3V: AquaB In-line Tubular Pipe (Venturi) & 10 \(\pm\) 1.3 \\ \hline
3C: AquaB In-line Tubular Pipe (Air Comp.) & 14 \(\pm\) 1.6 \\ \hline
4V: AquaB Radial Vortex (Venturi) & 16 \(\pm\) 2.1 \\ \hline
4C: AquaB Radial Vortex (Air Comp.) & 20 \(\pm\) 2.4 \\ \hline
5: Anzai Porous Membrane & 2.1 \(\pm\) 0.30 \\ \hline
3V: AquaB In-line (Off-Grid, incl. P-drop) & 8.6 \(\pm\) 1.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Negative exponential decay relaxation times, \(\tau\) (days), on the NB populations for the water-flow NB generators. \begin{table}
\begin{tabular}{l c} \hline \hline
**Type/Model** & \(\tau\) \\ \hline \hline
1: Moleaer Kingfisher & 1.4 \(\pm\) 0.25 \\ \hline
2: Acniti Turbiti 727 & 1.6 \(\pm\) 0.28 \\ \hline
3V: AquaB In-line Tubular Pipe (Venturi) & 10 \(\pm\) 1.3 \\ \hline
3C: AquaB In-line Tubular Pipe (Air Comp.) & 14 \(\pm\) 1.6 \\ \hline
4V: AquaB Radial Vortex (Venturi) & 16 \(\pm\) 2.1 \\ \hline
4C: AquaB Radial Vortex (Air Comp.) & 20 \(\pm\) 2.4 \\ \hline
5: Anzai Porous Membrane & 2.1 \(\pm\) 0.30 \\ \hline
3V: AquaB In-line (Off-Grid, incl. P-drop) & 8.6 \(\pm\) 1.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 8: NB populations (\(\times 10^{6}\) NBs per mL) and power from air-fed submersible NB generators sampled after 20 min of operation in 20 litres; the number of asterisks details the number of successful NB measurements from three separate samples. The number of asterisks shows the number of successful detections of nanobubbles out of three attempts. the total DO being in NB form (as opposed to about a quarter for the Acniti case). Although the submersible type of electric-field NB generation, with no forced water convection, does not match the absolute performance of its water-flow electric-field counterpart in terms of NB mass concentration, the more passive nature of quiescent NB generation and NB propagation throughout the water body via natural convection currents is clearly a very attractive \"passive\" NB-generation approach. The longer-lived nature of air NBs generated via the electric-field approach compared to hammermill rotation (with a relaxation time some five-times longer at 9 versus 1.8 days, cf. Table 8) is also a desideratum for long-lived and passive air-fed nano-oxygenation. Similar results were witnessed for nanocarbonation in this same AquaB-versus-Acniti submersible comparison [31]. Clearly, this type of more passive NB-generation approach is of interest to water-body aeration/gasification in outdoor settings, whether in environmental water bodies or in aeration/carbonation tanks.