Stability of nanobubbles generated in water using porous membrane system

Gas nanobubble dispersions as the important agent in environmental processes – generation methods review

“…The difference in the sizes of bubbles are explained by authors by stating that higher solubility of pure carbon dioxide (1688 mg/dm 3 at 20°C and 1 atm) over pure oxygen (43.4 mg/dm 3 at 20°C and 1 atm) and over pure nitrogen (19.0 mg/dm 3 at 20°C and 1 atm) causes formation of higher number of bubble nucleation sites what allows for generation of more bubbles of smaller diameter (Wang et al, 2019). Similar tendency of bubble size difference of gases of different solubility was observed by Ulatowski et al (2019) for nitrogen and oxygen nanobubbles.…”

“…In combination with non‐uniform spelling of the word ‘nanobubbles’ (as mentioned above) this fact makes it harder to gain access to information about nanobubbles, their properties and applications. Additionally, some papers report nanobubbles as gas domains covered in surfactant (frother) shell (Xu et al ., 2009; Krupka et al ., 2010; Wu et al ., 2012) and others reserve this name to distinguish gas domain without such shell (Takahashi et al ., 2007; Srinivas and Ghosh, 2012; Ulatowski et al ., 2019). The focus of this work was to examine the generation of gas bubbles in the liquid which are not adhered to the surface (‘bulk nanobubbles’).…”

“…This method is assuming the density (and as such internal pressure) of the gas inside the bubble. Most common method of calculating internal pressure is the usage of Young–Laplace equation; however, the literature is still proposing new correcting factors which describe the effects of surface charge (Yasui et al ., 2018; Ulatowski et al ., 2019). Similarly, for some of the process gases which are to be enclosed inside the nanobubbles, there are some chemical reactions which allow for determination of TDG (Total Dissolved Gas).…”

“…Dispersion of nanobubbles is extremely stable, being able to stay in liquid for days, weeks or months depending on liquid (Takahashi, 2005; Ohgaki et al ., 2010; Ushikubo et al ., 2010; Duval et al ., 2012; Liu et al ., 2013; Meegoda et al ., 2018). The reasons for such behaviour are not clear and are the subject of academic discussion (Bunkin and Bunkin, 1992; Seddon et al ., 2011; Bunkin et al ., 2012, 2016; Weijs et al ., 2012; Attard, 2013, 2016; Kleppestø, 2015; Alheshibri et al ., 2016; Yasui et al ., 2016; 2018; Oh and Kim, 2017; Ulatowski et al ., 2019). Nevertheless, most of researchers agree that at least one of the reasons of extraordinary longevity is the existence of surface charge on the gas–liquid interphase.…”

“…(2010), who measured dissolved oxygen using Clark electrode. However, as mentioned earlier, nanobubbles are reported as stable for weeks or even months, and as such the mass transfer between bubbles and surrounding liquid has to be prevented in some way (Weijs et al ., 2012; Bunkin et al ., 2016; Yasui et al ., 2016, 2018; Ulatowski et al ., 2019). Such gas‐liquid system has to reach the equilibrium state before the disappearance of nanobubbles.…”