The Science Behind Nanobubbles – Webinar Series Q&A

by Ragy Ragheb, Monday, 6th November 2023

nanobubbles

Moleaer and Malvern Panalytical cohosted three webinars on the science behind nanobubbles and how they are studied, measured and viewed. We’ve compiled all the questions that were asked during the webinars to provide you with a comprehensive overview.

Jump to the questions for each webinar:

If you’d like to access the recordings of these webinars, please visit them below:

Moleaer also has a large database of case studies for a variety of nanobubble applications.

Q&A for Part 1: The Science Behind Nanobubbles: An Introduction with Malvern Panalytical & Moleaer

Q1: Is there any electrostatic effect during the nanobubbles production and can this affect element relations between them or affect element elimination by plants?

A1: Yes, there is a critical role played by the electrostatic charges on the bubble. The charges interact with ions and charged molecules and ions to impact the availability to plants.

Q2: Do nanobubbles remove CO2 in water streams?

A2: It is possible to saturate water with another gas than CO2 using Moleaer technology to attent to remove CO2 for the water but we do not have any data to confirm it at this time.

Q3: If nanobubbles are suspended in a saturated solution of water, and the water becomes unsaturated, will the nanobubbles dissolve into the water or will they merge into larger bubbles?

A3: The nanobubbles are expected to be stable even if the surrounding water becomes unsaturated. The stability of nanobubbles is mainly determined by zeta potential and adsorbed species on the bubble surface. Gas exchange between the bubble and water medium is a secondary factor. For large bubbles, it is true that gas exchange will shrink the bubble but nanobubbles represent a special situation where surface tension and ionic forces work together to stabilize the bubble.

Q4: Do the nanobubbles destroy the biofilm of bio-filters in aquaculture?

A4: Nanobubbles can prevent biofilm formation but we do not have data/info about biofilters in aquaculture.

Q5: How about the aquaculture/aquarium industry segments?

A5: Both aquaculture and aquarium industries are great industries for nanobubble applications.

Q6: Is there any possibility to convey or store hydrogen inside the bubble?

A6:  Hydrogen nanobubbles can be made, but nanobubbles as storage devices is not compelling because the total amount you can store in nanobubbles is very small.

Q7: What is the neat surface tension of the nanobubble/water interface? Can this be measured?

A7: Theoretical models exist which estimate the effective surface tension by combining the Young Laplace equation with the charged surface energy component of the bubble surface. We are not aware of any instrument to measure the actual tension at the interface.

Q8: Have you done any research on what size of bubble is better for specific applications? For example, is it better a 200nm than 500nm for fish?

A8: Moleaer’s technology produces nanobubbles ~80 to 120 nm in diameter so all of the applications that we have developed have been for bubbles in that size range. We have not done the bubble size dependence on fish growth/survivability, nor have we seen published reports yet. 

Q9: What is the smallest scale of the Moleaer setup?

A9: About 10-15 gpm is the smallest.

Q10: How much do nanobubbles affect the pH level in the water? If has an effect to pH level what is the side effect? This point is important for us since pH levels affect element elimination and also control diseases like bacteria or fungi.

A10: The nanobubbles will lower the pH.

Q11: Does pressure affect the system and if so, what is the desired pressure?

A11: Gas and liquid pressure in the generator have a significant effect on gas transfer and bubble formation. Generally higher pressures favor better dissolution and bubble formation.

Q12: Some farmers are using useful bacteria for their production. Do you think the nanobubbles can kill these useful bacteria?

A12: Nanobubbles can kill beneficial bacteria depending on their sensitivity, but they also enhance the growth and multiplication of such bacteria by providing a better oxygen environment and nutrient availability. The net result is a more beneficial population.

Q13:  What are the pros and cons of the different ways of producing nanobubbles?

A13: There are a couple of factors – scalability of the design (i.e., volume range of flow), operating environment (clean vs. dirty water of various degrees of solids), energy requirement, size of bubbles, number of bubbles, zeta potential, etc.  It is not possible to list every method and their pros and cons here, however, there has been a lot of research on different applications by institutions and universities.

Q14: What are the cost effects and cost differences to other methods like venturi or liquid oxygen if we use nanobubble technology since crop production costs are increasing nowadays?

A14: All these methods can provide DO (dissolved oxygen) but not all methods will provide nanobubbles (e.g., venturi’s generally provide large bubbles). The nanobubbles have their own distinct role to play in plant and soil health. So, the cost analysis has to take into account the full scale of benefits and not just elevated DO levels.

Q15: If I have a nanobubble water sample in a spectrophotometer will the bubble interfere with the reading?

A15: Yes, there will be a background scattering of light by the nanobubbles. It should be broad and should not interfere with specific peaks of molecular absorption.

Q16: How stable are nanobubbles? And, under elevated pressure?

A16: We have seen weeks and months in lab conditions. Some papers have reported more than a year. The bubbles are expected to survive high pressures.

Q17: How stable/sustainable are nanobubbles under elevated temperatures?

A17: These bubbles survive elevated temperatures before boiling. I am not sure what happens during boiling.

Q18: Can you freeze the Nanobubble water, if yes, what is the shelf/half-life?

A18: Yes, freeze-fracture is one method of detecting nanobubbles. The bubbles maintain shape during the freezing process. We do not know how long it can be maintained in the frozen state, but there is evidence from ice geology that bubbles trapped in arctic/Antarctic regions maintain character for hundreds of years. However, nanobubbles are disapearing when the water thaws.

Q19: Does freezing destroy nanobubbles?

A19: Freezing is one of the ways to preserve bubbles for freeze-fracture microscopy study. But nanobubbles are then destroyed when the water thaws.

Q20: How does the formation of nanobubbles change if you use ambient air or do something in a glove box and make nanobubbles out of nitrogen? Or another gas?

A20: Nanobubbles have been made using a variety of gases. So, there is no limitation on the choice of gas.

Q21: How many/what percentage of nanobubbles were detected 8 days after aeration?

A21: In the lab, we have seen values within +/- 10% even after weeks of storage.

Q22: Do all algal species respond adversely to nanobubbles? Are oxygen nanobubbles more effective than air nanobubbles in algal control?

A22: Oxygen nanobubbles are more effective for algal control. All three broad algal groups respond to nanobubble treatment.

Q23: Do you guys have actual experiments to decide the gas volume or mass in the bubbles? Rather than using the ideal gas law to calculate.

A23: We have not done actual experiments to measure gas in bubbles. Sensitive techniques are not yet available.

Q24: What are the power requirements for a typical Moleaer setup? In other words, what is the efficiency?

A24: Energy consumption depends on a variety of factors. It’s best to talk with a Moleaer expert to help answer specific application, sizing, and energy questions. Please feel free to reach out to info@moleaer.com for more information.

Q25: Do you have any applications for BOD reduction in aeration? Specifically, in WWTPs?

A25: Yes, air nanobubble pretreatment of screened, raw wastewater beneficially modifies influent wastewater characteristics (COD fractionation) which enables wastewater process intensification of downstream physical separation and activated sludge processes resulting in a reduction in aeration energy requirements and chemical consumption as well as improved effluent water quality (e.g., higher BOD and ammonia removal rates).

Q26: How stable is the nanobubble and does it remain that way if it’s combined with irrigation water through subsurface drip irrigation? How long does it stay stable in soil solution? Also, does it have any effect on liquid fertilizer that is also incorporated in the water?

A26: Briefly, we do not have methods to directly measure the NB in soil. But we can see the effect it is having on salts in the soil and the impact on root zone development. We know it is doing something even though we cannot see it. For fertigation, we expect that nanobubbles will improve efficacy and limit scaling due to precipitation. This is an area of research at this time.

Q27: If I am making Microbubbles, is it possible there are Nanobubbles present too?

A27: Yes, depending on your production method you could have mircobubbles present together with nanobubbles.

Q28: If the bubble gas is 0.01% then the gas-to-liquid ratio is 1:9999. Microfoam for firefighting is G:L of ~2:98

A28: The amount of gas contained in nanobubbles is not of any consequence. The gas gives the bubble shape and size. The real value of nanobubbles is in their surface charge which is able to impact a vast number of chemical and ionic interactions. For firefighting, you need foam volume which only big bubbles can provide. Pre-existing nanobubbles could change the number and size of microbubbles and have an indirect effect. When the microbubbles nucleate, the presence of nanobubbles could help to nucleate more uniform-sized foam or denser foam.

Q29: Is it possible to use nanoparticle technology to dissolve CO2 in water more efficiently?

A29: The shear method that Moleaer uses has very high efficiency (>85%) for transferring gas into water. CO2 transfer would be even more efficient because of its solubility in water.

Q30: How are the nanobubbles destroyed? What is the lifetime of nanobubbles?

A30: Nanobubbles can be destroyed by several methods – ultrasound, shock wave, pressure fluctuations, UV, etc. Nanobubbles also naturally self-destruct through coalescence. Under lab conditions, nanobubbles can be stable for months.

Q31: Is there a good way to eliminate bubbles from a solution?

A31: Yes, strong shock can eliminate nanobubbles. Even sparging with air may eliminate them.

Q32: What is the nanobubble stability when you use it in the sea, thinking in high NaCl concentrations?

A32: As per theory, salt solutions decrease the zeta potential around the bubble which decreases the bubble stability leading to coalescence. However, seawater has many other components beyond salt, and they may have an opposite effect, i.e., make the bubble more stable even if salt makes it less stable.

Q33: Have you examined nanobubbles and how they behave under extreme conditions? For example, are they still there after boiling or freezing?

A33: After freezing, yes, the bubbles remain in the ice, but not after thawing. After boiling we are not sure. However, we know bubbles survive elevated temperatures.

Q34: How do you destroy them? Is the dissolved gas that the Moleaer machines make also stable? Or what is its “shelf life”?

A34: The dissolved gas is governed by Henry’s law. The liquid amount will change depending on pressure, temperature, and water composition. The bubbles can be destroyed by energetic means such as ultrasound, shock, energy stimulus like UV, etc.

Q35: Does this structure of charges in the slipping plane form a surface plasmon resonance on a nanobubble surface?

A35: I have not seen the plasmon theory for double layers. In analogy to metals, the outer charge could have plasmon characteristics. But I have not seen any reports myself.

Q36: What is preventing the widespread application of nanobubble technology?

A36: It is a young field. It has been in the curiosity stage for the last 20 years. But now a huge number of applications are being developed around the world. Commercial scalability is one problem with many nanobubble generation methods which has kept the technology at the lab level. But technologies like that of Moleaer are having success in many tough applications like wastewater treatment and irrigation. In the coming years, we expect the technology to proliferate rapidly in many markets.

Q37: What laser have you used for the nanobubble measurement? Green laser? And what is the power of the laser? If you used deionized water as a control, what is the concentration of Particles in DI water?

A37: We prefer the green laser, <5mW.

Q38: Does this work for all gases? And what happens with the bubble at the end of the lifetime: escape or solve?

A38: It works for all gases. The nanobubbles may ultimately coalesce or collapse either naturally or through external stimulus.

Q39: How good are nanobubbles at reducing the nitrogen in wastewater streams?

A39: Air nanobubble pretreatment of screened, raw wastewater has been shown to improve fine bubble aerations oxygen transfer efficiency, and nitrification by removing contaminants like fats, oils, grease, and surfactants that inhibit physical separation and activated sludge processes. Further, nanobubble pretreatment of screened, raw wastewater has been shown to prevent septicity in primary clarifiers to further prevent the solubilization of ammonia from the sludge blanket which reduces the ammonia load to the activated sludge process. The reduction in ammonia load also improves denitrification rates by reducing the amount of nitrate that needs to be removed by the biological process. This phenomenon is best described as nanobubble-enabled wastewater process intensification.

Q40: Why are nanobubbles charged negatively? Are other types of bubbles negatively charged?  

A40: Most water-air interfaces are charged negatively. This is due to the hydroxyl ions that are available in water naturally. This is true for any bubble.

Q41: Is this method limited to the concentration of nanobubbles?

A41: Nanobubble concentration is dependent on the production method as well as water quality. Also, Malvern Panalytical equipments can measure other types of nanoparticles with the same method.

Q42: What kind of water is best for long-term stability or holding of both nanobubbles and dissolved o2? Deionized, distilled, reverse osmosis, mineral, etc.?

A42: Basic water (high pH) provides high zeta potential and thus high bubble stability.

Q43: Effects on using nanobubble in combination with AOP in aquaculture?

A43: Generally, AOP is used for treating persistent chemicals that cannot be easily destroyed.  We are not aware of the application of AOP in aquaculture together with nanobubbles. Nanobubbles can probably add to the oxidizing power of AOP and improve its efficacy. This is an area currently studied in Moleaer R&D lab.

Q44: What is the best temperature range of fluid for your system?

A44: Our systems operate in the 5-60C range in various geographies and climates. In any non-freezing environment to desert environment.

Q45: How do you know the effects you see in the different applications are because of nanobubbles versus dissolved, or because both are present?

A45: Dissolved gases can be introduced without nanobubbles by techniques such as sparging or venturi. And the difference can then be determined against nanobubble generators that inject both dissolved gas as well as nanobubbles.

Q46: The 3 T’s degrade macro or microbubbles “Time, Temp. Turbulence”. Is the same true for nanobubbles?

A46: Yes, the three T’s are relevant, except it takes more amount of the three T’s to destroy nanobubbles compared to micro/macro bubbles.

Q47: What happens when the nanobubble water goes through a freeze-thaw cycle?

A47: We know it survives the freeze (because it retains shape as observed in microscopy). On thawing, a significant proportion is destroyed as per some publications and internal tests at Moleaer.

Q48: What is the maximum stable concentration of nanobubbles before foaming?

A48: According to literature, concentrations above 1 billion/mL have been prepared with no evidence of foaming, except for some haziness in the liquid.

Q49: What is the control sample you used? Di water?

A49: DI water or tap water (when tap water is used to make bubbles) is the control. Sometimes salt water is the control.

Q50: Do microbubbles have the same properties and uses as the Nanno?

A50: In general, they have similar properties except for the magnitude of those properties. For example, Microbubbles have a much shorter lifetime before they coalesce and rise. Microbubbles also do not carry as much total charge as nanobubbles do.

Q&A | How nanobubbles improve agriculture input efficiency and plant health

Q&A for Part 2: The Science Behind Nanobubbles: How nanobubbles improve agriculture input efficiency and plant health

Q1: What are the highest DO levels you can achieve using O2 nanobubbles?

A2: For O2 it is around 40ppm (as per Henry’s law) and for air, it is around 8-9ppm O2 in water.

Q2: Can you share the reference articles discussed?

A2: Moleaer has several research articles in our Resource Center.

Q3: Is there any correlation between the type of gas for nanobubble and surface tension?

A3: We do not have clean data on this relationship.

Q4: What is the concentration of bubbles (particles per volume) that you can reach?

A4: A UCLA study by Michael K. Stenstrom confirmed just short of 1 billion nanobubbles per milliliter of water when supersaturating.

Q5: Any observations with heavy metals in soil, specifically in organic field production?

A5: There are publications that discuss the effect of Arsenic in rice paddy fields where nanobubbles were employed.

Q6: Can nanobubbles kill biofilters in aquaculture or aquaponics?

A6:  Although nanobubbles have some antimicrobial properties, the net effect in aquaculture (or any bio-environment) is to promote the growth and efficacy of aerobic species.

Q7: Are nanobubbles produced in solid or liquid presentation?

A7: Nanobubbles are created in liquid media.

Q8: You mention high internal bubble pressure. The bubble is also extremely stable. Do you have a methodology to burst nanobubble and measure the energy release?

A8: We don’t know of a methodology to burst and measure the energy released.  There are some theoretical papers that discuss it.

Q9: Would nanobubbles survive having materials mixed with water prior to application?

A9: Yes, nanobubbles can survive in dirty water or water with dissolved or suspended solids.

Q10: Do any of your leafy green growers use LED lighting to supplement or replace natural sunlight?

A10: Yes.

Q11: Can you share any information on the treatment of bacteria like pseudomonas?

A11: Human pathogenic bacteria like listeria have been treated with oxygen nanobubbles and shown to be effective.

Q12: What is the maximum salinity for measuring Zeta potential and NanoSight Microscope?

A12: 260 mS/cm is the maximum conductivity and 40% w/v is the maximum concentration for measuring zeta potential with the Zetasizer.   You can learn more about how salinity affects the Debye screening and thus zeta potential measurements in our blog. There isn’t a maximum salinity for using the NanoSight as long as the salts remain in solution and do not start precipitating.

Q13: How do nanobubbles affect foliar feeding or IPM?

A13: This is an area of active investigation.  In due time, data will be available.

Q14: Are nanobubbles beneficial for a hand-watering application?

A14: Yes, there are some benefits but we don’t have data to share yet.

Q15: Can we use Zeta potential and NanoSight for a non-aqueous system?

A15: You can measure Zeta potential for a non-aqueous system by using the Dip Cell Kit (ZEN1002).   You can read more about which cuvettes to use with your Zetasizer in this blog.   NanoSight is primarily used for aqueous based samples. 

Q16: Would you recommend aerating your foliar spray solution with nanobubbles to improve wettability?

A16: There are nanobubble fertilizers on the market today, and some of their products are designed to be applied with a foliar spray.

Q17: Are you thinking about a bench-scale nanobubble generator (about 1 to 2 liters per treatment) for in-depth laboratory work?  Is this even possible?

A17: Yes, we are looking into bench/lab scale development.

Q18: If a body of water already has a negative electrical charge (like – 400 mV) and you inject NB, will you increase or decrease the overall electric charge?

A18: There is a shielding effect from existing charges, the net charge on the bubble will change.

Q19: How long do nanobubbles typically survive in water? Would they last in a water tank for several days before being pumped out? Are they sensitive to shipping if we use a water tanker truck?

A19: This depends on water quality. For example, in clean irrigation water, nanobubbles can last weeks if not longer but will reduce with agitation and time.  If in a sealed vessel, longevity will be improved with limited sloshing.

Q20: How can NBs work effectively over cost of operation vs. yield in agriculture applications?

A20: The Moleaer methodology of working with agricultural clients is to collaboratively construct objectives, metrics, units of measurement and timing of measuring inputs and outputs to determine the ROI of using nanobubbles. This methodology is crop and site-specific.

Q21: The nanobubble assists in the degradation of biofilms, do they also degrade algal blooms (HAB)?

A21:  Yes, nanobubbles help reduce harmful algal blooms (HABs).

Q22: What is the effect of Nanobubble concentration in agriculture?

A22: We don’t directly size our equipment using nanobubble concentration, but we rather look at the benefits nanobubbles can offer. For example, DO improvement is determined by several factors, including the type of waterbody, amount of water, customer goals and other factors. We treat water in holding ponds and also “in-line” with existing irrigation systems. When we treat water in ponds we determine the volume of the pond, size of the pond, inflows and outflows to determine if compressed air, oxygen or ozone is the optimal gas source and the volume of oxygen required. Nanobubble concentration can be measured on the field after installation as confirmation that our equipment is working properly.

Q23: Are there studies/information available on health impacts to humans in drinking nano-oxygenated water?

A23: No controlled studies have been reported.

Q24: Are there any differences in NB behavior/properties in saltwater vs. freshwater?

A24: Yes, bubble size, concentration and zeta potential are all affected by saltwater.  There are various publications addressing this subject.

Q25: Can we use Nanobubbles in organic agriculture?

A25: Yes, you can use it in organic agriculture. 

Q27: Any information on how nanobubbles affect soil fungi?

A27: Nanobubbles promote beneficial soil fungi.

Q28: Does the use of nanobubbles in irrigation distribution systems allow farms to reduce the use of nutrients such as Nitrogen and Phosphorus?

A28: Several of our customers have seen reduced fertilizer usage. Nanobubble technology helps improve nutrient uptake efficiency and nutrient mobility.

Q29: In irrigation source water hygiene, how do nanobubbles differentiate between beneficial bacteria and non-beneficial bacteria in water or soils?

A29:  Nanobubble technology helps create and maintain an aerobic condition in the rhizosphere.  In oxygen-rich soils and substrates, beneficial bacteria thrive, while in anaerobic conditions, pathogens tend to thrive.

Q30: Explain the limit of 200mS/cm max salinity.

A30: The reason we have a limit of 250 mS/cm (a bit above the stated 200 in the question) for the Zetasizer is because polarization occurs at the electrodes under high ionic strength conditions. We have further addressed this by Constant Current Mode measurements which mitigate this polarization balancing the effective voltage at the electrodes. You can read more about the fundamentals of zeta potential in this technical note.   You can also learn how the Zetasizer Advance series addresses high conductivity in this blog and this paper. 

Q31: If the MB generator creates both microbubbles and nanobubbles, can the device differentiate only nanobubbles?

A31: The NanoSight’s analytical range is 10nm – 1000nm for size analysis as noted in our brochure.   Malvern Panalytical can also analyze larger particles up to 10 microns with the Zetasizer and up to 3.5mm with the Mastersizer.  The NanoSight range is primarily used for nanobubbles size analysis and is a number-based technique that enables you to gate in different size ranges and note the concentration and percentage of each sub-population. 

Q32: Is Moleaer NB generator suitable for use in saltwater conditions, e.g. marine aquaculture?

A32: Yes, Moleaer NB generators are suitable for saltwater in aquaculture.

Q33: Can NBs influence the germination of seeds?

A33: Yes, there are many publications showing the effect of NB on seed germination.

Q33: Please explain in more detail the zeta potential distribution. How can we use it as evidence of nanobubble’s existence in the solution?

A33: Mixed materials may reduce the zeta potential and hence reduce bubble stability on mixing.  It depends on how the mixed material affects the zeta potential. Comparing Zeta potential of a solution before and after nanobubble injection can give some indications on the presence of nanobubbles.

Q34: Is the NS fluorescence option relevant to nanobubbles measurements?

A34:You do not need fluorescence to measure the size and concentration of nanobubbles with NanoSight.   However, there are some groups that will form nanobubbles with lipid layers where the lipids might be fluorescently tagged.   This would afford the use of the fluorescence filter to look at labelling efficiency.  

Q35: Are nanobubbles safe to drink?

A35: In theory, since nanobubbles are naturally occurring, however, there have been no scientifically controlled studies.

Q36: What is the concentration of bubbles (particles per volume) that you can reach?

A36: Just short of 1 billion per ml can be achieved and was documented by UCLA.

Q37: Do you have a webinar on aquaculture and nanobubbles in aquaculture? Specifically increasing DO and energy requirement per g of O2 compared to other methods.

A37: This will be in the future when we gather more experimental data. Moleaer presented at the 2022 World Hatchery Forum and you can access this recording until we release new ones.

Q38: Does your device need registration as a plant protection product within the EU market?

A38: We do not claim crop protection, instead we are strengthening root development plant health through improved water quality to prevent and reduce the use of pesticides.

Q39: How do the nanobubbles react when they come in contact with different types of beneficial bacteria in the medium?

A39: Nanobubble technology helps create and maintain an aerobic condition in the medium, which encourages the growth of beneficial bacteria.

Q40: Does nanobubble use cause oxygen supersaturation?

A40: Oxygen will reach saturation at a particular pressure according to Henry’s law.  Once the pressure is reduced, the water will temporarily be in an over-saturation state till it equilibrates to the new pressure.

Q41: Are nanobubble devices now available on a lab scale and with low costs?

A41: We are looking into bench/lab scale development.

Q&A for Part 3: The Science Behind Nanobubbles: How nanobubbles solve tough problems at Water Resource Recovery Facilities

Q1: What products do you have related to nanobubble generation within sewer collection systems (i.e., Wet wells and force mains to control odor and corrosion)?  

A1: At this time, Moleaer’s nanobubble generators require the wastewater to be screened to protect the pump and nanobubble generator internals. We do have installations in wet wells and lift stations where either the wastewater is screened or free of large debris and fibrous materials. However, Moleaer is actively working on a collection system solution and does have a product under development for the collection system.

Q2: When nanobubbles navigate do all the attached surfactants get removed?

A2:   The extent of surfactants removed is a function of water quality, nanobubble dose, reaction time, and surfactant concentration. Moleaer has observed the complete conversion of slowly biodegradable soluble COD to readily biodegradable soluble COD with sufficient doses of nanobubbles injected into flowing wastewater.

Q3: Do surfactants make the nanobubble unstable?

A3: Higher nanobubble concentrations are measured in the presence of surfactants, salts, and other common water contaminants. Such contaminants serve as nucleation points for nanobubbles to form and also stabilize the nanobubbles. However, the fate and longevity of the nanobubble are a function of many variables including water quality. It is the interaction/reaction of nanobubbles with contaminants, dissolved gases, energies, and other surfaces/interfaces in the wet environment that destabilizes the nanobubble.

Q4: Briefly clarify how the nanobubbles scavenge the surfactants.

A4: The surfactants are attracted by the hydrophobic surface of the nanobubbles. The pressure and temperature released and the possible hydroxyl radical generated during nanobubble collapse break down the surfactants, likely breaking the hydrophobic tail from the hydrophilic head which changes the molecular structure of the compound by making it non-polar and more readily biodegradable.

Q5:  Can nanobubble concentration be determined in partially treated wastewater?

A5: Nanobubble concentration can only be measured in clean water samples. There is too much interference from nano- and larger particles to measure nanobubble concentration in wastewater.

Q6: How would this system be applied to a below-grade collection tank/lift station that has manhole access and is located below a road/parking lot?  I.e. – there is limited availability at the ground level to station equipment.

A6: At this time, Moleaer’s nanobubble generators require the wastewater to be screened to protect the pump and nanobubble generator internals. We do have installations in wet wells and lift stations where either the wastewater is screened or free of large debris and fibrous materials. However, Moleaer is actively working on a collection system solution and does have a product under development for the collection system.

Q7: Can you please talk more about the end products of surfactant removal/destruction by nanobubbles (what remains from surfactant after NBs treatment)?

A7: Roughly 2% to 10% of the total COD is removed during nanobubble pretreatment of raw, screened municipal wastewater suggesting that some surfactants may be degraded all the way to water and CO2. The byproducts of the remaining surfactants that are not completely degraded will depend on the surfactant type and the degradation step that the reaction stopped at. Moleaer has observed the complete conversion of slowly biodegradable soluble COD to readily biodegradable soluble COD with sufficient doses of nanobubbles injected into flowing wastewater.

Q8: Where do the surfactants go after interacting with NB if not into the sludge?  How/where are they disposed of?

A8: The surfactants are removed/partially degraded during nanobubble treatment. Roughly 2% to 10% of the total COD is removed during nanobubble pretreatment of raw, screened municipal wastewater suggesting that some surfactants may be degraded all the way to water and CO2. The byproducts of the remaining surfactants that are not completely degraded will depend on the surfactant type and the degradation step that the reaction stopped at. Moleaer has observed the complete conversion of slowly biodegradable soluble COD to readily biodegradable soluble COD with sufficient doses of nanobubbles injected into flowing wastewater.

Q9: Hello, were you able to achieve readings repeatability of the nanobubble concentration and size?

A9: Yes, you can get repeatability with good experimental controls and training. 

Q10: Can we measure Zeta potential with particle size with Nanosight Pro?

A10: If you are interested in Zeta Potential, please consider our Zetasizer.  The NanoSight NS300 and NanoSight Pro can measure size, concentration and fluorescence.

Q11: What kind of gas did you use for surfactants mitigation, do you have any idea about other gases?

A11: The gas supply recommended for nanobubble pretreatment of wastewater is compressed air because it is affordable and widely available. However, pure oxygen and high-purity oxygen gas supplies have also been used.

Q12: Is there any specific reason why nanobubbles were not added in the secondary treatment?

A12: The surfactants need to be pretreated upstream of the biological process to prevent the surfactants from binding to the biosolids. Also, the dose of nanobubbles required to treat mixed liquor is much higher than the dose required to treat raw wastewater due to the interaction of nanobubbles with biomass. Treating the mixed liquor requires significantly more nanobubble treatment resulting in much larger pumps and nanobubble generators compared to treating raw wastewater. The interaction with NB and surfactants is found to have a better contact time for a reaction to occur. Extra Organic matter in secondary treatment competes with the NB. We have done it, but the best efficiency is achieved when NBs are injected prior to physical separation processes (such as clarifiers, DAFs, etc.). This allows for higher surfactant removal and provides higher efficacy.

Q13: How is the foaming property of different surfactants in the presence of different nanobubbles?

A13: Since there are many different types of surfactants in wastewater, the effect of NBs on individual surfactants is unknown. However, foaming in municipal wastewater is significantly reduced as a result of nanobubble pretreatment.

Q14: How do you see this playing a role in the larger decarbonization and ESG strategies?

A14: Pretreating raw wastewater with nanobubbles has the potential to dramatically shift the energy balance by preventing solids from solubilizing and reducing the soluble organic and nutrient load to the secondary treatment process. Further, removing surfactants from wastewater makes wastewater easier to treat; thereby generating more biogas and reducing the amount of infrastructure, chemicals, and energy required to maintain effluent water quality.

Q15: If NB are so effective why are they not more widely used – can NB be naturally formed?

A15: Yes, nanobubbles occur in nature. They were first discovered in crashing ocean waves. Nanobubbles are a relatively new field of study because it has only been within the last decade or so that the analytical equipment required to measure and quantify nanobubbles has been available. Further, Moleaer’s patented shear method for producing nanobubbles is one of the few if not only methods of generating nanobubbles at scale in flowing wastewater. Moleaer was formed in 2016 and started selling large-scale nanobubble generators in 2021. One issue is awareness, which we are trying to improve.  We are seeing increasing adoption in yield and energy-intensive industries. 

Q16: Have you introduced this into the more conventional CHP (combined heat & power) central plants and/or microgrids?

A16: This is an area we are investigating for possible implementation.

Q17: What is the longevity of NBs in wastewater? Any idea?

A17: The longevity of nanobubbles in wastewater depends on water quality, surface interaction, and dissolved oxygen levels. As such, nanobubble reactions and interactions are dynamic and dependent on many variables. Also, there are no known analytical methods for directly measuring nanobubbles in wastewater due to the interference of other nano- and larger particles. When injecting air nanobubbles into raw, screened municipal wastewater, the conversion of slowly biodegradable soluble COD to readily biodegradable soluble COD generally takes around 15 to 30 minutes so it may be fair to assume that nanobubble longevity in wastewater is about the same as the COD reaction time.

Q18: Can you please talk more about the end products of surfactant removal/destruction by nanobubbles (what remains from surfactant after NBs treatment)?

A18: Roughly 2% to 10% of the total COD is removed during nanobubble pretreatment of raw, screened municipal wastewater suggesting that some surfactants may be degraded all the way to water and CO2. The byproducts of the remaining surfactants that are not completely degraded will depend on the surfactant type and the degradation step that the reaction stopped at. Moleaer has observed the complete conversion of slowly biodegradable soluble COD to readily biodegradable soluble COD with sufficient doses of nanobubbles injected into flowing wastewater.

Q19: How were nanobubbles generated? Was there the issue of quick temperature rise?

A19: The nanobubbles were generated using a Moleaer nanobubble generator. Moleaer’s nanobubble generators use the shear method to produce nanobubbles. During nanobubble production, the only heat that is measurably added to the system by Moleaer’s nanobubble generator is from heat loss from the pump motor to the water and the heat loss from the compressed air gas supply to the water. Nanobubble concentration can only be measured in clean water samples. There is too much interference by nano- and larger particles to measure nanobubble concentration in wastewater. In tap water, Moleaer’s nanobubble generator generates hundreds of millions of nanobubbles per milliliter. Higher nanobubble concentrations are achieved in the presence of surfactants, salts, and other common water contaminants.

Q20: How do nanobubbles affect foam fractionation?

A20: This is unknown, but an area of interest that should be evaluated as part of a future study. 

Q21: How is the surfactant removed after treatment?

A21: The surfactants are removed/partially degraded during nanobubble treatment. The pressure and temperature released and probably also the hydroxyl radical generated during nanobubble collapse and break down the surfactants, likely breaking the hydrophobic tail from the hydrophilic head which changes the molecular structure of the compound by making it non-polar and more readily biodegradable. Surfactants break down, removing their dual property of Hydrophilic and hydrophobic, and are no longer detected as surfactants, organic parts would be degraded further in secondary treatment.

Q22: When nanobubbles cavitate do all attached surfactants get removed?

A22: The extent of surfactants removed is a function of water quality, nanobubble dose, reaction time, and surfactant concentration. Moleaer has observed the complete conversion of slowly biodegradable soluble COD to readily biodegradable soluble COD with sufficient doses of nanobubbles injected into flowing wastewater.

Q23: Can you provide us with a range, minimum size, and price for the largest project and price?

A23: Moleaer’s nanobubble generators generally range in hydraulic capacity from 10 gpm to over 4500 gpm. Price varies widely based on the nanobubble solution package requirements and installation geography. Please contact Moleaer with project location and application specifics for pricing range.

Q24: How long does NB stay active? Are they more effective with hydrogen?

A24: It depends on water chemistry.

Q25: Were you able to achieve repeatability when measuring the NB concentration and size? And may you comment on the NB stability?

A25: Yes, you can get repeatability with good experimental controls and training.  In clean water at room temperature without any disturbance, stability has been reported to be months.

Q26: Is this a sale or a multi-year service agreement contract?

A26: The contract agreement will depend on the geographic location of the installation and the treatment capacity of the nanobubble generator. Generally, low-flow equipment is available for lease or sale and larger equipment is available for lease with an option to purchase it at a significantly discounted price after 3 years.

Q27: Does temperature increase due to bubble generator affect bubble size and concentration?

A27: Moleaer’s nanobubble generator uses the shear method to produce nanobubbles. During nanobubble production, the only heat that is measurably added to the system by Moleaer’s nanobubble generator is from heat loss from the pump motor to the water and the heat loss from the compressed air gas supply to the water. If recirculated for a long time the temp could increase.  With Moleaer equipment we don’t see any significant increase.

Q28: Will adding Ozone to Oxygen increase the performance?

A28: The gas supply recommended for nanobubble pretreatment of wastewater is compressed air because it is affordable and widely available. However, pure oxygen and high-purity oxygen gas supplies have also been used. Ozone at a sufficient dose would degrade the surfactants, but Moleaer has not tested ozone nanobubbles for surfactant removal since degradation occurs using safer, less corrosive, and more affordable gases like air or oxygen. Pretreatment NB of WW uses air, not required other gas sizes the interaction is with NB regardless of the gas source. Ozone can be used for other applications like disinfestion for example.

Q29: Can you provide us with different sizes and prices?

A29: Moleaer’s nanobubble generators generally range in hydraulic capacity from 10 gpm to over 4500 gpm. Price varies widely based on the nanobubble solution package requirements and installation geography. Please contact Moleaer with project location and application specifics for pricing range.

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