Microbubble technology has been gathering much attention in many fields, including foam fractionation, food processing, purification processing of polluted water, and marine culture of oysters (Kodama et al., 2000; Ohnari and Tsunami, 2006; Takahashi, 2005). Successful applications of microbubbles to bioprocessing of polluted water and to aquaculture have been reported (Ohnari, 2007). Microbubbles are tiny gas bubbles with a mean diameter of 50 μm or less in water (Ohnari and Tsunami, 2006; Takahashi, 2005). One of the most significant characteristics of a microbubble is that it shrinks in water and ultimately collapses because it resides in water for a long time (Zhang et al., 2007); in contrast, ordinary macrobubbles quickly rise and burst at the surface of water (Takahashi et al., 2003). Therefore, microbubbles are a highly efficient means of delivering dissolved gas into a solution. A crucial characteristic of the microbubble is that they are electrically negative charged (ζ potential) on their surface (Ohnari and Tsunami, 2006; Takahashi, 2005); due to these charges, the bubbles do not attract each other and thereby get larger and attract positively charged materials. Because of these characteristics, microbubbles have significant potential to be used for a variety of practical purposes.
However, almost no information is available regarding how microbubbles affect vegetative plant growth in hydroponic culture systems. The objective of the present study was to examine the effect of microbubbles on the growth of leaf lettuce in a deep flow technique (DFT) hydroponics culture system. To understand the effects of microbubbles on plant growth, we compared lettuce treated with macrobubbles generated by aquarium aeration stones at a similar level of aeration.
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Takahashi, M., Kawamura, T., Yamamoto, Y., Ohnari, H., Himuro, S. & Shakutsui, H. 2003 Effect of shrinking microbubbles on gas hydrate formation J. Phys. Chem. B 107 2171 2173
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