Exploring the Fascinating Universe of Nanobubbles

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Exploring the Fascinating Universe of Nanobubbles

What Are Nanobubbles?

Nanobubbles are tiny gas-filled cavities that exist in aqueous solutions, measuring less than 200 nanometers in diameter. To put this into perspective, they are about 1/1000th the width of a human hair! Due to their minuscule size, they possess unique properties different from those of macro or microbubbles. These properties have led to a surge of interest in various sectors like healthcare, agriculture, and water treatment. Industrial application of nanobubbles has exponentially increased over the past two decades as the scientific research around them.

Foudas, A. W., Kosheleva, R. I., Favvas, E. P., Kostoglou, M., Mitropoulos,
A. C., & Kyzas, G. Z. (2023). Fundamentals and applications of nanobubbles: A review.

Nanobubble size classification, according to ISO-20480–1–2017, is given in Fig. 2. Larger bubbles quickly rise to the surface of a liquid and collapse. Nanobubbles which are < 1 micro meter in diameter will randomly drift owing to what is termed, Brownian Motion and can remain in liquids for an extended period of time

Historical Development and Discovery

The concept of nano-sized particles has been explored for decades, but it wasn’t until advanced microscopy and particle measurement technologies became available that nano bubbles were distinctly identified and studied in-depth. The initial research into nano bubbles focused primarily on their existence, formation, and basic properties.

The latter part of the 20th century saw a surge in nanotechnology, with nano bubbles becoming a subject of intrigue. Scientists realized that these tiny entities had potential far beyond just being microscopic gas bubbles in a liquid. In the early 2000s, with the boom in nanoscience and the development of precise instruments, the understanding of nano bubbles deepened. Their stability in liquid mediums, coupled with their unique interaction with surrounding materials, led to the exploration of their application in diverse sectors.

From a historical standpoint, the journey of nano bubbles parallels the broader trajectory of nanotechnology. As our capacity to manipulate and understand the nano-world grew, so did our appreciation for these tiny bubbles and the enormous potential they held within.

Research publication since 2017 with “nanobubble technology” as search term; (a) publications by sector and (b) number of published works per year. Foudas, A. W., Kosheleva, R. I., Favvas, E. P., Kostoglou, M., Mitropoulos, A. C., & Kyzas, G. Z. (2023). Fundamentals and applications of nanobubbles: A review.

Physical Properties That Set Them Apart

1. Longevity:

Unlike their larger counterparts, which rise to the surface and burst within seconds, nanobubbles demonstrate an uncanny ability to remain stable in water for prolonged periods, often several weeks or even months. This stability opens up a plethora of opportunities for applications that were previously deemed impossible.

Scientific references

  • Nirmalkar, N., Pacek, A. W., & Barigou, M. (2018). On the Existence and Stability of Bulk Nanobubbles. Langmuir : The ACS Journal of Surfaces and Colloids, 34(37), 10964–10973. https://doi.org/10.1021/acs.langmuir.8b01163
  • Meegoda, J. N., Aluthgun Hewage, S., & Batagoda, J. H. (2018). Stability of nanobubbles. Environmental Engineering Science, 35(11), 1216–1227. https://doi.org/10.1089/ees.2018.0203

2. Charged Surface:

One of the defining features of nanobubbles is their negatively charged surface. This characteristic ensures they repel each other, preventing them from coalescing easily. This negative charge also means they can attract and neutralize positively charged contaminants, offering vast potential for water purification and other environmental applications.

3. High Internal Pressure:

Due to their diminutive size, nanobubbles possess an internal pressure much higher than that of macroscopic bubbles. This property can be harnessed in various innovative ways, including drug delivery mechanisms where the pressure can assist in propelling medicine to targeted cells.

One of the less obvious, yet highly beneficial implications of this high pressure is the ‘scouring‘ effect of nanobubbles. As these bubbles move through pipes and emitters, their heightened internal pressures give them a robust cleaning capability. They effectively “scour” or scrub away deposits, residues, and potential blockages, ensuring that pipes remain clean and operational. For industries where pipeline efficiency is paramount—like wastewater treatment or food processing—this natural cleaning mechanism can reduce maintenance costs and prolong equipment life.

How to calculate the internal pressure of bubbles?

The Young-Laplace equation describes the pressure difference between the inside and outside of a bubble (or a droplet) due to surface tension. It’s given by:

ΔP=2σ/r

Where:

  • ΔP is the pressure difference (or the excess pressure inside the bubble).
  • σ is the surface tension of the liquid the bubble is in.
  • r is the radius of the bubble.

To apply this formula, we need the surface tension of the liquid in which the bubble is formed. For this example, let’s consider the bubble is in water. The surface tension of water at room temperature is approximately 0.072N/m.

Let’s calculate the internal pressure ΔP for some given diameters:

Scientific references

4. Rising Velocity:

Rising Speed of Bubbles

The rising speed of a bubble in a fluid (like water) can be estimated using Stokes’ law for small Reynolds numbers (laminar flow conditions). The equation for the terminal velocity Vt (rising speed) of a bubble is given by:

Where

  • Vt is the terminal velocity.
  • ρb is the density of the bubble (for air at room temperature and atmospheric pressure, approximately 1.225 kg/m3).
  • ρf is the density of the fluid (for water, approximately 1000 kg/m3).
  • g is the acceleration due to gravity (9.81 m/s29.81 m/s2).
  • r is the radius of the bubble.
  • η is the dynamic viscosity of the fluid

Let’s calculate the rising speeds for the given bubble diameters, in mm/h

Note that the negative sign indicates that the bubbles are rising (since the bubbles are lighter than water). The absolute value gives the magnitude of the rising speed in mm/h.

As with the previous calculations, these results are approximations and may vary depending on factors such as temperature, bubble coalescence, and turbulence. The Stokes’ law estimation is most accurate under laminar flow conditions.

Scientific references

  • Sakr, M., Mohamed, M. M., Maraqa, M. A., Hamouda, M. A., Aly Hassan, A., Ali, J., & Jung, J. (2022). A critical review of the recent developments in micro–nano bubbles applications for domestic and industrial wastewater treatment. Alexandria Engineering Journal, 61(8), 6591–6612. https://doi.org/10.1016/j.aej.2021.11.041

4. Gas Exchange Abilities:

At the heart of many industrial and environmental processes lies the pivotal role of gas-liquid mass transfer. Whether it’s aerating wastewater or providing a conducive environment for microorganisms, the efficiency of this process can significantly impact outcomes. Nanobubbles are revolutionizing this domain. Let’s delve deeper into their impact and mechanisms.

  1. Increased Mass Transfer Area: The rate of gas transfer is contingent on the mass transfer area between gas and liquid phases. Nanobubbles boast a substantially greater surface area, facilitating quicker gas dissolution, even to a supersaturated state.
  2. Smaller Bubble, Greater Efficiency: The diminutive radius of MNBs, coupled with their augmented internal pressure, turbocharges the mass transfer rate to the surrounding liquid. Given that the diffusion rate of gas is proportional to the pressure gradient, it’s evident that reduced bubble sizes can exponentially bolster gas transfer efficiency.

Decoding the Math Behind Mass Transfer Rate

The rate at which two phases transfer mass can be discerned by considering:

  • The liquid-gas mass transfer coefficient.
  • The concentration gradient within the phases.
  • The surface-area-to-volume ratio.

Let’s make by calculating the surface area of individual bubbles and then the total surface area of all such bubbles in one milliliter (1 mL) of water, we first need to establish how many bubbles of each size can fit in 1 mL. Then, we calculate the surface area of a single bubble of each size, and finally determine the total surface area for all the bubbles in that volume.

In summary:

  • The total surface area of 0.1 mm bubbles in 1 mL of water is approximately 1.5×10−4 m2.
  • The total surface area of 120 nm bubbles in 1 mL of water is approximately 0.05 m2.

This means the 120 nm bubbles have 333.33 times more surface area than the 0.1 mm bubbles when considering the same volume (1 mL) of water.

Disclaimer: The above calculations assume that 1 ml of water is fully saturated with both 0.1mm and 120nm bubbles. While this isn’t reflective of real-world scenarios, it provides a conceptual illustration.

Techniques for Measuring and Characterizing Nano Bubbles

As the application areas for nano bubbles expand, the demand for efficient production and accurate characterization techniques grows concurrently. The continued evolution of these methods promises a more profound understanding of nano bubbles and their potential to revolutionize various sectors. Below you’ll find a list of different ways of measuring and characterizing nanobubbles.

1. Dynamic Light Scattering (DLS): This technique measures the size distribution of nano bubbles. A laser beam is passed through the sample, and the scattered light intensity is analyzed to determine the size of the particles, including nano bubbles.

2. Nanoparticle Tracking Analysis (NTA): NTA visualizes and analyzes particles in liquids, allowing users to view and measure nano bubbles in real-time.

3. Laser Doppler Electrophoresis: This method determines the zeta potential of nano bubbles, providing insights into their stability and surface charge.

4. Microscopy Techniques: Techniques such as Scanning Electron Microscopy (SEM) or Atomic Force Microscopy (AFM) provide high-resolution images of nano bubbles, offering detailed insights into their morphology and structure.

Example of characterization of a solution containing nanobubbles using MalVern Panalytical Nanosight system.
Sample derived from Kairospace treated water.

Latest Techniques in the Generation of Nano Bubbles

Below, we elucidate the most advanced methods used to generate these marvels:

1. Hydrodynamic Cavitation:

Principle: Hydrodynamic cavitation is a phenomenon rooted in fluid dynamics. The key to this method is manipulating pressure conditions to induce the formation and eventual collapse of vapor bubbles.

Methodology: The process begins by introducing a constriction, like an orifice or a venturi tube, into a flowing liquid’s path. This constriction generates a significant drop in the liquid’s pressure. As the liquid surges through this narrowed path, vapor bubbles emerge due to the reduced pressure. But these bubbles are transient. As they move downstream and encounter regions with comparatively higher pressure, they implode. This sudden collapse gives birth to a myriad of nano bubbles.

2. Ultrasonic Cavitation:

Principle: At its core, ultrasonic cavitation is the transformation of sound waves into pressure variations within a liquid, leading to the genesis of vapor-filled bubbles.

Methodology: High-frequency ultrasonic waves are propagated through the liquid. These sound waves result in alternating high and low-pressure cycles. During the low-pressure phases, minuscule vapor-filled cavities or bubbles form. However, as the high-pressure phase ensues, these bubbles experience a rapid compression, causing them to collapse. This cyclical birth and death of bubbles via sound waves ultimately produce nano bubbles in abundance.

3. Gas Diffusion:

Principle: Gas diffusion leverages the principles of solubility and the tendency of gases to escape from a supersaturated solution.

Methodology: Initially, a solution is supersaturated by forcing a gas into a liquid under controlled, high-pressure conditions. Think of this as the liquid taking a deep breath, holding in more gas than it typically would at equilibrium. When this high pressure is suddenly released, the liquid “exhales,” releasing the gas it held within. But instead of large bubbles, a cascade of nano bubbles forms, as the supersaturated gas emerges out of the solution in a burst of effervescence.

4. Electrolysis: Splitting Molecules to Create Bubbles

Principle: Electrolysis is the process of driving a chemical reaction using an electric current. When applied to water, it splits water molecules into oxygen and hydrogen gases.

Methodology: Electrodes are submerged into an electrolyte solution, typically water with some added salts to enhance conductivity. When an electric current is passed through the solution, water near the cathode produces hydrogen gas, while water near the anode produces oxygen gas. The emerging gases form as nano bubbles due to the minute scale of electrochemical reactions at the electrode surfaces.

At Kairospace, we’ve meticulously integrated these four groundbreaking techniques into our workflow, adapting each approach to align with specific application requirements. The brilliance of these methods lies not just in their individual efficacy, but also in their potential for synergistic combinations. By fusing elements of Hydrodynamic Cavitation, Ultrasonic Cavitation, Gas Diffusion, and Electrolysis, we’ve unlocked new paradigms of efficiency in nano bubble production. This collaborative approach ensures that nano bubbles can be precisely tailored to serve a diverse array of applications.

Scientific references

  • Arwadi, O. El, & Zuruzi, A. S. (2022). Towards Bulk Nanobubble Generation: Development of a Bulk Nanobubble Generator Based on Hydrodynamic Cavitation. International Journal of Recent Advances in Mechanical Engineering (IJMECH), 11(2). https://doi.org/10.14810/ijmech.2022.11201
  • Zimmerman, W. B., Tesař, V., & Bandulasena, H. C. H. (2011). Towards energy efficient nanobubble generation with fluidic oscillation. Current Opinion in Colloid and Interface Science, 16(4), 350–356. https://doi.org/10.1016/j.cocis.2011.01.010
  • Ulatowski, K., Sobieszuk, P., Mróz, A., & Ciach, T. (2019). Stability of nanobubbles generated in water using porous membrane system. Chemical Engineering and Processing – Process Intensification, 136(December 2018), 62–71. https://doi.org/10.1016/j.cep.2018.12.010
  • Azevedo, A., Etchepare, R., Calgaroto, S., & Rubio, J. (2016). Aqueous dispersions of nanobubbles: Generation, properties and features. Minerals Engineering, 94, 29–37. https://doi.org/10.1016/j.mineng.2016.05.001

Ok, thanks for reading so far! We have painted an overall picture of what nano bubbles are and some of their properties, now let’s jump to the fun part, let’s talk about their applications.

Innovative Applications of Nano Bubbles Across Key Industries

Unlocking Agricultural Potential with Nano Bubbles

In the vast field of agriculture, nano bubbles are making a significant splash. Here’s a dive into their transformative impact:

1. Revolutionizing Soil Aeration

Healthy, aerated soil is the bedrock of thriving crops. Traditional methods of soil aeration can be labor-intensive and not always effective. Enter nano bubbles: their minuscule size allows them to penetrate soil particles more efficiently, ensuring that roots receive an optimal supply of oxygen. This not only promotes robust root systems but also enhances nutrient absorption, leading to healthier, more bountiful crops.

To offer a more tangible perspective on the potency of nano bubbles, consider the following picture that showcases the results our state-of-the-art system deployed at a prestigious golf course. The results speak volumes. There’s a pronounced improvement in root development, heightened soil aeration, enhanced water infiltration, and a noticeable reduction in salt compaction. The greens not only look better but are also healthier from root to tip. Get the full report at this link.

Scientific references

  • Zhou, Y., Bastida, F., Liu, Y., He, J., Chen, W., Wang, X., Xiao, Y., Song, P., & Li, Y. (2022). Impacts and mechanisms of nanobubbles level in drip irrigation system on soil fertility, water use efficiency and crop production: The perspective of soil microbial community. Journal of Cleaner Production, 333(November 2021), 130050. https://doi.org/10.1016/j.jclepro.2021.130050

2. Bolstering Plant Growth

Plants, much like humans, require specific conditions to thrive. Introducing nano bubbles into irrigation systems can significantly boost plant growth. The micro-oxygenation provided by these bubbles ensures that plants receive the optimal oxygen levels they need, fostering faster growth, stronger resilience, and better yields.

The following image transports you to a modern vertical farm – a testament to innovative agriculture. With the incorporation of nano bubbles, the results are nothing short of transformative. There’s a remarkable 35% increase in fresh weight, BRIX (sugar content) levels see a surge of 15%, and the time to harvest is expedited by a substantial 10%. These aren’t mere numbers; they’re a glimpse into the future of farming, powered by nano bubbles. Get the full report here.

Disclaimer: Results will vary depending on the installation.

Scientific references

3. Eco-Friendly Disease Control

Disease and pests are the nemeses of any farmer. Nanobubbles, with their unique properties, are proving to be game-changers in combating plant diseases. By optimizing water quality and delivering targeted oxygen levels, these bubbles can curtail the growth of harmful pathogens and minimize the spread of diseases, reducing the need for chemical interventions. When used in tandem with ozone or other disinfectants, nanobubbles can enhance the antimicrobial action, ensuring that harmful bacteria, fungi, and viruses are effectively eradicated. The tiny bubbles increase the contact surface of the disinfectant, making the elimination of pathogens more efficient.

4. Promoting Seed Germination

Seeds, nature’s encapsulated wonders, have the innate potential to flourish into vast crops or towering trees. Traditional cultivation practices, while effective, often leave untapped potential in seed germination. Here’s where nanobubbles come into play. These tiny bubbles, when introduced into the water, block the action of enzymes that prevent germination and improve oxygenation at the root level, fostering an environment conducive to rapid and healthy seed growth. The increased oxygen availability directly aids in breaking the seed’s dormancy quicker, leading to accelerated sprouting. As a result, with nanobubble technology, farmers can harness the full potential of seeds, paving the way for enhanced yields and reduction on the time seedlings spend at the nursery.

Scientific references

  • Ahmed, A. K. A., Shi, X., Hua, L., Manzueta, L., Qing, W., Marhaba, T., & Zhang, W. (2018). Influences of Air, Oxygen, Nitrogen, and Carbon Dioxide Nanobubbles on Seed Germination and Plant Growth. Journal of Agricultural and Food Chemistry, 66(20), 5117–5124. https://doi.org/10.1021/acs.jafc.8b00333
  • Liu, S., Oshita, S., Makino, Y., Wang, Q., Kawagoe, Y., & Uchida, T. (2016). Oxidative Capacity of Nanobubbles and Its Effect on Seed Germination. ACS Sustainable Chemistry and Engineering, 4(3), 1347–1353. https://doi.org/10.1021/acssuschemeng.5b01368

5. Food Washing

Nanobubbles offer a revolutionary approach to food washing, ensuring a deeper and more thorough cleanse due to their tiny size. They effectively remove chemical residues and contaminants by oxygenating the food surface and, when combined with disinfectants, provide superior antimicrobial action while reducing their use. This technology not only enhances food safety but also prolongs shelf life, all while being eco-friendly and leaving no harmful residues. In essence, nanobubbles promise cleaner, safer, and longer-lasting fresh produce.

Scientific references

  • Burfoot, D., Limburn, R., & Busby, R. (2017). Assessing the effects of incorporating bubbles into the water used for cleaning operations relevant to the food industry. International Journal of Food Science and Technology, 52(8), 1894–1903. https://doi.org/10.1111/ijfs.13465

Call for action!

We are looking for a grower that would like to enhance plant growth.

To enhance plant growth, we’ve conceptualized a dynamic approach that harnesses the power of various gases at strategic times of the day. For instance, we recommend introducing oxygen nanobubbles during the morning hours. This strategy aims to boost photosynthesis and stimulate metabolic processes, setting the tone for an active day of growth. As the sun sets, transitioning to hydrogen nanobubbles can support cellular functions in the absence of sunlight. Moreover, periodic applications of CO2 nanobubbles as a foliar spray can further augment the photosynthetic potential of plants. This holistic approach, tailored to the plant’s natural rhythms, aims to maximize growth and overall plant health.

Revolutionizing Water Treatment Processes

Applications of Nanobubbles in Water Treatment

1. Purification

Creating Healthier Drinking Water Nanobubbles play an instrumental role in water purification. When nanobubbles burst, they produce reactive oxygen species (ROS). These ROS can effectively disinfect water, eliminating harmful pathogens and ensuring it’s safe for consumption. Moreover, nanobubbles also aid in coagulation processes, helping remove tiny suspended particles from the water.

Scientific References

  • Singh, B., Shukla, N., Cho, C. H., Kim, B. S., Park, M. H., & Kim, K. (2021). Effect and application of micro- and nanobubbles in water purification. Toxicology and Environmental Health Sciences, 13(1), 9–16. https://doi.org/10.1007/s13530-021-00081-x
  • Batagoda, J. H., Hewage, S. D. A., & Meegoda, J. N. (2018). Nano-ozone bubbles for drinking water treatment. Journal of Environmental Engineering and Science, 14(2), 57–66. https://doi.org/10.1680/jenes.18.00015

2. Waste Water Treatment

A Sustainable Approach to Reuse and Recycle Wastewater often contains organic pollutants, heavy metals, and other contaminants. Nanobubbles can intensify the oxidation process, breaking down these pollutants and making the water suitable for reuse. The ability of nanobubbles to elevate dissolved oxygen levels also aids in fostering the growth of beneficial aerobic bacteria, which further helps in breaking down organic waste.

Scientific References

  • Atkinson, A. J., Apul, O. G., Schneider, O., Garcia-Segura, S., & Westerhoff, P. (2019). Nanobubble Technologies Offer Opportunities to Improve Water Treatment. Accounts of Chemical Research, Table 1. https://doi.org/10.1021/acs.accounts.8b00606
  • Gurung, A., Dahl, O., & Jansson, K. (2016). The fundamental phenomena of nanobubbles and their behavior in wastewater treatment technologies. Geosystem Engineering, 19(3), 133–142. https://doi.org/10.1080/12269328.2016.1153987

3. Flotation Processes

Efficient Solids Separation In flotation processes, nanobubbles can be utilized to attach to solid particles, aiding in their separation from the liquid phase. Their minute size ensures a higher surface area, resulting in more efficient flotation compared to traditional methods.

Scientific References

  • Calgaroto, S., Wilberg, K. Q., & Rubio, J. (2014). On the nanobubbles interfacial properties and future applications in flotation. Minerals Engineering, 60, 33–40. https://doi.org/10.1016/j.mineng.2014.02.002
  • FAN, M., TAO, D., HONAKER, R., & LUO, Z. (2010). Nanobubble generation and its application in froth flotation (part I): nanobubble generation and its effects on properties of microbubble and millimeter scale bubble solutions. Mining Science and Technology, 20(1), 1–19. https://doi.org/10.1016/S1674-5264(09)60154-X

4. As Cleaning Agents

A Deep-Clean without the Chemicals Nanobubbles can be generated using various gases, including ozone. Ozone nanobubbles possess strong oxidation properties, making them exceptional cleaning agents. They can effectively remove stains, biofilms, and other stubborn residues from surfaces without the need for chemical detergents.

Scientific References

Zhu, J., An, H., Alheshibri, M., Liu, L., Terpstra, P. M. J., Liu, G., & Craig, V. S. J. (2016). Cleaning with Bulk Nanobubbles. Langmuir, 32(43), 11203–11211. https://doi.org/10.1021/acs.langmuir.6b01004

5. Degradation of Organic Pollutants

Combating the Pollutants Head-on Organic pollutants in water bodies are a rising concern. Nanobubbles can catalyze advanced oxidation processes, which can effectively break down these organic pollutants. By generating hydroxyl radicals upon bursting, nanobubbles can degrade even the most resilient of contaminants, ensuring cleaner waterways.

Scientific References

  • Xia, Z., & Hu, L. (2018). Treatment of organics contaminated wastewater by ozone micro-nano-bubbles. Water (Switzerland), 11(1). https://doi.org/10.3390/w11010055
  • GARRIDO, I., MARTÍNEZ, C. M., FLORES, P., HELLÍN, P., CONTRERAS, F., & FENOLL, J. (2023). Remediation of amide pesticides polluted soils by combined solarization and ozonation treatment. Pedosphere, 2005(09), 1–25. https://doi.org/10.1016/j.pedsph.2023.03.003

Benefits of Using Nanobubbles in Water Treatment

  • Eco-friendly Approach One of the standout benefits of employing nanobubbles in water treatment is its eco-friendly nature. They reduce the reliance on chemical treatments, leading to lesser environmental impacts and ensuring that the treated water is free from chemical residues.
  • Cost-Efficient With their ability to enhance processes like flotation and purification, nanobubbles can lead to significant cost savings in water treatment operations. Furthermore, their role in reducing chemical usage further adds to the cost benefits.
  • Versatility Nanobubbles can be generated using various gases, making them versatile for different applications, from ozone-based cleaning to oxygenation in wastewater treatment.

Conclusion

Nanobubbles are clearly setting the tone for the future of water treatment. Their multifaceted applications, from purification to pollutant degradation, make them an invaluable asset in our pursuit of cleaner, safer water. As research and innovations continue in this field, we can anticipate even more groundbreaking applications that will further reinforce the importance of nanobubbles in water treatment and beyond.