Enhanced degradation of benzo[a]pyrene and toxicity reduction by microbubble ozonation

Microbubbles and their application to ozonation in water treatment: A critical review exploring their benefit and future application

“…Wu et al (2019) observed a 1.15 -1.7 times higher steady state ozone concentration for microbubble ozonation across the pH range 3 -11 when compared to conventional bubble systems. Steady state concentrations that were 1.1 (Chu et al, 2007), 1.15 (Zheng et al, 2015), 1.23 (Nam et al, 2019) and 2.7 (Takahashi et al, 2012b) times higher have also been observed. Zhang et al (2018) did not observe a significant difference between microbubble and conventional bubble steady state concentrations, with reported ozone concentrations of 5.5 and 5.7 mg L -1 , respectively.…”

“…In some cases, automatic gas suction is achievable through the introduction of a pressure from a rapidly rotating impeller, but such systems are often used in conjunction with a gas supply (Wu et al, 2019). There is currently little published evidence of large scale application for ozonation using these types of microbubble generator, with the highest reported liquid flow rate of 4.5 m 3 hr -1 (Nam et al, 2019). These types of microbubble generator are often limited by their capacity for gas flow, which is often only a small percentage of the liquid flow capacity.…”

“…There have been several studies that have directly compared the ozone kLa for microbubbles and conventional bubbles (Gao et al, 2019;Nam et al, 2019;Shin et al, 1999;Wu et al, 2019;Xu et al, 2012;Zhang et al, 2018;Zheng et al, 2015). The range of kLa values reported for microbubbles at pH 7 ranged between 0.09 -1.5 min -1 and between 0.1 -1.4 min -1 for conventional bubbles (Figure 3).…”

“…For a given superficial gas velocity, several comparisons of microbubbles and conventional bubbles are available (Figure 6). It has been found that the average kLa enhancement factor is 2.3 ± 1.3 where the minimum enhancement was 1.2 times (Nam et al, 2019) and the maximum was 5.2 times (Zhang et al, 2018). Studies that have looked at the effect of superficial gas velocity for microbubble kLa have been undertaken but have not been directly compared with results from conventional bubbles.…”

“…The enhanced gas utilization efficiency infers that less ozone is required in order to achieve a target ozone residual. Based on the difference in kLa for direct comparisons of conventional bubbles with microbubbles, it may be possible to reduce reactor volume by between 16 and 81% when using microbubbles (based on the minimum and maximum kLa enhancement seen by Nam et al (2019) and Zhang et al (2018) respectively), while still achieving similar or better residual ozone concentration (Figure 15). As a consequence, a smaller nominal ozone contactor volume when using microbubbles might be feasible when compared to systems develop using conventionally sized bubbles.…”