Micro-nano Bubbles Research Articles

Generation of micro-nano bubbles by self-developed swirl-type micro-nano bubble generator

The fabrication of bubble generator with high micro-nano bubble generation efficiency has always been challenging. Strong turbulence is considered to be beneficial. Herein, we developed a swirl-type micro-nano bubble generator by equipping a variable-pitch spiral cavitation reactor to enhance the shear breakage effect of bubbles. The variable-pitch spiral guide vanes and central column were innovatively installed into the cavitation reactor to generate swirling liquid flow so as to intensify gas-liquid contacting and mixing. The effect of geometric parameters on the flow field structure was investigated through numerical simulations and the optimum structure was obtained. Then the lab-scale swirl-type micro-nano bubble generator was manufactured to conduct flow tests. The bubbles with size down to 0.301 μm were generated. In addition, the bubble generator displayed superior oxygen enrichment capacity, which was higher than that of the traditional venturi tube. The insights from this study provide a guideline for the development of efficient micro-nano bubble generators.

Enhanced permeate flux by air micro-nano bubbles via reducing apparent viscosity during ultrafiltration process.

Micro-nano bubbles (MNBs) play important roles in the reduction of membrane fouling during membrane separation; however, such improvements are always attributed to the reduced concentration polarization on the surface of membranes and little attention has been paid on the variations of physicochemical properties of the feed caused by MNBs. In this study, the separation efficiencies of the feed containing humic acid (HA), bovine serum albumin (BSA), sodium alginate (SA) or dyes can be improved by MNBs during ultrafiltration, and the normalized fluxes can be maximally increased to 139% and 127% in the dead-end and cross-flow modes, respectively in the treatment of HA solution. We further reveal that the decreased apparent viscosity of the feed in the presence of MNBs is the key factor that enhances the normalized flux during ultrafiltration. This study gives new insight on the importance of MNBs in membrane separation and provides valuable clues for other chemical processes.

Removal of chlorine-contaminated groundwater by two-stage ozonation and biostimulation methods.

Trichloroethene (TCE) contamination is a critical environmental hazard, and the substrate options for its biostimulated remediation are limited. This study applied an ozonation-and-biostimulation process to remove TCE from groundwater. The substrate used, denoted as Transferred Energy Element (TEE), was composed of natural organic materials and had a low viscosity (2.914cP). Ten batch experiments were conducted through the application of micro-nano bubbles (MNBs) and substrates (TEE and EOS® [emulsified oil substrate]). MNBs with an average diameter of 157.5-180.8nm effectively degraded TCE and dichloroethane within 6min. Biostimulation using the TEE substrate effectively degraded both TCE and vinyl chloride pollutants and reached a steady state after 25 days. The two-stage dechlorination procedure with MNB treatment as the first stage enhanced TCE removal via biostimulation. MNBs reduced the TCE concentration in the first 20min, but increased the chloride (Cl-) concentration over the following five days (∼80mg/L). The procedure with biostimulation as the first stage and 20min ozonation as the second stage reduced the Cl- concentration by ∼10mg/L. The Cl- concentrations rebounded after day 25 in the EOS environment. X-ray diffraction revealed that the released Na+ from the TEE settled with Cl- as minerals in the soil. The novel two-stage method for TCE removal was found to be more effective than solo MNB treatment or biostimulation.

Degradation Mechanism of Micro-Nanobubble Technology for Organic Pollutants in Aqueous Solutions.

Micro-nanobubbles (MNBs) technology has emerged as an effective means of sewage treatment, while the molecular mechanism for its pollutant degradation is still unknown. In this paper, the reactive molecular dynamics simulation technique is used to study the degradation mechanism of pollutants caused by shock-induced nanobubble collapse. We first demonstrate that the propagating shock wave can induce nanobubble collapse, and the collapsing nanobubble has the ability to focus mechanical energy via the converging motion of liquid in the interior of the bubble, leading to the formation of a high-speed jet with a much higher energy density. We also unveil the mechanical nature of long-chain pollutant degradation and the mechanism of free radical generation. Due to the impacting jet, the high-gradient flow has the ability to stretch the long-chain molecule and cause mechanical scission of the molecule in a homolytic manner. Finally, our simulation results reveal that adding ozone molecules to the collapsing bubble would introduce an additional dehydrogenation mechanism.

Integrated MnO2 nanosheet ultrafiltration ceramic membrane with micro-nano bubbles for catalytic treatment of dye wastewater

Membrane filtration integrated with micro-nano bubbles (MNBs) is an attractive technology for treating dye wastewater given its efficiency and environmental compatibility. However, the amount of ·OH generated during the disintegration of MNBs is insufficient in practical applications. This work presents the characterisation of a modified Al2O3 ceramic membrane (CM) with the MnO2 nanosheet (MnO2/Al2O3 CM), which provides dual functions of membrane filtration and MNB catalysis. Here, a novel MNB catalytic membrane reactor (MNB-CMR) was constructed by applying the modified MnO2/Al2O3 CM for treating the simulated dye wastewater, i.e., methylene blue (MB). The MB degradation showed that the MNB-CMR improved 17% decolorization rate and 20% total organic carbon removal rate compared to the integrated MNB process with the non-modified CM. The MNB-CMR exhibited excellent catalytic performance and fouling resistance. Besides, the effects of MNB-CMR operational parameters such as the initial methylene blue (MB) concentration, reaction temperature, solution flux, and solution pH on the MB degradation performance were investigated. Based on the scavenging experiments of reactive oxygen species (ROS), the reaction of singlet oxygen (1O2) or hydroxyl radicals (·OH) was elucidated as the primary ROS responsible for the oxidation of MB in the MNB-CMR. In addition, the XPS results showed that the redox couple of Mn(IV)/Mn(III) on the surface of the MnO2/Al2O3 CM was responsible for MNB catalysis. Finally, we proposed a possible degradation pathway of MB. This work shows an attractive alternative wastewater treatment process to relieve membrane fouling and enhance MNB catalysis concurrently.

The Application of Ozone Micro-nano Bubble Treatment Vegetable Fresh-Keeping Technology in Air Logistics Transportation

In recent years, fresh fruits and vegetables have been sought after by Chinese people. The fresh-keeping technology, storage, and transportation of fruits and vegetables have also attracted a large number of people’s attention. Various methods of preservation, storage, and transportation of fruits and vegetables have begun to appear in the society. Micro and nanobubbles have the characteristics of long stay time, larger than the surface, high surface negative electricity, strong reliability, high efficiency of heat transfer, can cause oxygen free radicals, can greatly improve the actual effect of ozone and ozone utilization rate, and reduce the operation cost. This article aims to study the application of ozone micro-nano bubble processing vegetable fresh-keeping technology in air logistics and transportation, and put forward the idea of applying ozone micro-nano bubble processing fresh-keeping technology to fruits and vegetables fresh-keeping and transportation more widely. This article focuses on the introduction of ozone micro-nano bubbles, fresh-keeping technology, air transportation, and experiments on some fresh-keeping technologies in the article. The experimental results show that the vegetable preservation technology based on ozone micro-nano bubbles can better maintain the moisture and nutrients in the vegetables. The preservation technology of ozone micro-nano bubble treatment has improved the preservation of fruits and vegetables by 12%.

Comparative study on direct and indirect methods for wet desulphurisation and denitrification based on micro-nano bubbles

ABSTRACT The wet desulphurisation and denitrification technique based on micro-nano bubbles, which is available by either D-method or I-method, is a promising novel process. By employing piped water, Na2SO3 aqueous solution and HA-Na aqueous solution as the absorption liquids, a comparative study was conducted in this article on D-method and I-method to analyze their performance, advantages and disadvantages. It was accompanied by an investigation of how initial pH and initial temperature values of the absorption liquids affected the removal efficiency. The results suggested a positive correlation between NO/SO2 removal efficiencies and pH values but a little improvement in the removal efficiency under alkaline conditions. Furthermore, heating the absorption liquids inhibited the removal of NO and SO2. When manipulated in the same experimental environment, D-method and I-method did not present a significant difference in the SO2 removal efficiency, while the former was remarkably more effective than the latter in removing NO. To put together, D-method had higher removal efficiency, but required a large-scale micro-nano bubble generator to process a large quantity of flue gas as the micro-nano bubble generator was subject to a limited inlet flow rate. Consequently, an increase in investment and operating costs was incurred, while this issue could be avoided by I-method.

Synergistic Treatment of Congo Red Dye with Heat Treated Low Rank Coal and Micro-Nano Bubbles.

In this study, the adsorption method and micro-nano bubble (MNB) technology were combined to improve the efficiency of organic pollutant removal from dye wastewater. The adsorption properties of Congo red (CR) on raw coal and semi-coke (SC) with and without MNBs were studied. The mesoporosity of the coal strongly increased after the heat treatment, which was conducive to the adsorption of macromolecular organics, such as CR, and the specific surface area increased greatly from 2.787 m2/g to 80.512 m2/g. MNBs could improve the adsorption of both raw coal and SC under different pH levels, temperatures and dosages. With the use of MNBs, the adsorption capacity of SC reached 169.49 mg/g, which was much larger than that of the raw coal at 15.75 mg/g. The MNBs effectively reduced the adsorption time from 240 to 20 min. In addition, the MNBs could ensure the adsorbent maintained a good adsorption effect across a wide pH range. The removal rate was above 90% in an acidic environment and above 70% in an alkaline environment. MBs can effectively improve the rate of adsorption of pollutants by adsorbents. SC was obtained from low-rank coal through a rapid one-step heating treatment and was used as a kind of cheap adsorbent. The method is thus simple and easy to implement in the industrial context and has the potential for industrial promotion.

Influencing factors and kinetics study on the degradation of gaseous ethyl acetate by micro-nano bubbles.

As an eco-friendly technology, micro-nano bubbles have gained extensive attention due to their excellent properties. We carried out the experiments to investigate the degradation performance of micro-nano bubbles on ethyl acetate at ambient temperature and pressure. The effects were deeply analyzed by studying the treatment time, initial concentration, and mixed components on ethyl acetate. Treatment time at 30 min had the best results, with a removal efficiency of 86.07 % and a degradation rate of 0.340 ± 0.021 min-1. With the increase of the initial ethyl acetate concentration, the degradation extent first increased and then decreased. The best efficiency of 94.61% and the maximum reaction rate of 8.79×10-3 min-1 were achieved at an initial concentration of 265.6 mg/m3. In addition, ethyl acetate degradation was inhibited by the presence of butyl acetate, and removal efficiency of mixed components was lower than that of single components. The GC-MS results showed that possible intermediates, such as ethanol and acetone, were produced during the decomposition process, which was expected to eventually decompose into CO2 and H2O as the reaction progresses. This work presents a new method for the degradation of ethyl acetate and provides valuable information for the degradation of organic matter by micro-nano bubbles.

Treatment of Wastewater-CPL by Biochar-Based Fenton-Like Catalyst in the Presence of Micro-nano Bubbles

Treatment of Wastewater-CPL by Biochar-Based Fenton-Like Catalyst in the Presence of Micro-nano Bubbles

Kinetics of CO2 gas bubbling for the separation of residual solvent from waste solids: Effects of bubble size

Solvent loss in the residual solids has been considered as a major challenge during the solvent extraction processes of unconventional oil ores (oil sands, asphalt rocks, etc.) or similar liquid-solid extraction. Meanwhile, the residual solvent in the solvent-extracted solids also causes serious environmental problems. The gas (CO2) bubbling process is proved to be an effective method for the removal and recovery of residual solvents from solvent-extracted solids. Herein, the kinetic model of the solvent removal by the gas bubbling has been built after considering the bubbling process as quasi vapor-liquid equilibrium. It is found that the solvent removal by gas bubbling matches well with the first-order kinetic model. Based on the fitting of gas bubbling experimental data under different water volumes, the quasi Henry’s constant and separation rate constant were obtained. At this time, all the related parameters of gas bubbling kinetic model were determined. Then the effect of bubble size on the gas bubbling kinetics was systematically analyzed, a potential strengthening method of connecting micro-nano bubbles and large bubbles is proposed for improving the solvent removal from the residual solids. Finally, the molecular dynamic (MD) simulation and gas bubbling experiments combined with large bubbles and micro-nano bubbles prove micro-nano could well accelerate the solvent removal in the residual solids. This work provides the fundamental basis for the industrialization of the gas bubbling process for the solvent removal from residual solids, which also provides a new idea for the treatment of environmental problems, such as the treatment of solvent-containing waste solids.

Micro-nano bubbles assisted laccase for biocatalytic degradation of bisphenols

Bisphenols are important industrial materials for example for the production of plastics, but are also well known for their adverse health effects, in particular bisphenol A (BPA) is an endocrine disruptor. The widespread use of plastics has raised concerns. Therefore, the removal of bisphenols from wastewater has sparked the interest of the scientific community. This work introduces a novel hybrid technique of micro-nano bubbles assisted laccase (MNB-Lac) to degrade bisphenols in water. The feasibility of MNB-Lac using BPA as a model contaminant was evaluated by comparing with MNB, Lac, ultrasound (UL), UL-Lac, and UL-MNB-Lac. Comprehensive investigations were carried out to understand the specific influences of key process parameters including the initial pollutant concentration, temperature, air intake, pH, outlet pipe length, and Lac concentration on BPA degradation. The alkaline environment and extended length of outlet pipe could improve the degradation efficiency further. MNB-Lac exhibited 2.3–6.2 folds higher BPA degradation and less time than the other above process under the optimal parameters. The mechanism of MNB-Lac revealed that the generation of hydroxyl radical, high O2 solubility, and high mass transfer efficiency induced by MNB play important roles on enhancing the degradation catalyzed by Lac. MNB-Lac was successfully used for treating bisphenol B, bisphenol C, and the mixture of three bisphenols with high removal efficiency. Subsequently, these degradation products were analyzed by GC–MS. MNB-Lac potentially represents an innovative technology with considerable advantages in contaminant cleanup and time efficiency for treating phenolic contaminated water. Furthermore, the findings provide new insights into the enhancement of the performance of an oxidizing enzyme by introducing MNB technology.

Enrichment of microplastic pollution by micro-nanobubbles

Microplastic pollution has become a global environmental concern. It has been reported that microplastics are easily accessible to a wide range of aquatic organisms and ultimately enter the human body along the food chain. They pose a severe threat to ecosystems, organisms and even human health due to their durability and persistence. However, how to reduce microplastic pollution still remains a challenge in terms of scientific techniques and policy-making. There is currently still a lack of effective methods for microplastic recycling and removal. Luckily, a new technique, micro-nanobubbles (MNBs), may provide a possible and highly effective method to enrich microplastic pollution: their great advantages[1] include a high specific surface area, long lifetime and ability to adsorb microplastics of the same size and hydrophobicity. Then they further adsorb on larger bubbles such as microbubbles or millimeter bubbles and float to the water surface together. In this study, we present a new method using MNBs to enrich microplastic pollution with high efficiency. Two types of microplastics, millimeter-scale plastic fragments and microplastic particles, were chosen as the model microplastic pollution systems to study the enrichment efficiency of MNBs on microplastics. Results showed that MNBs can efficiently enrich these microplastics. The enrichment efficiency increases with flotation time until a maximum value is reached. It is proved that MNBs not only collect the microplastic pollution but also reduce detergent use in domestic laundry sewage. This is because detergent, as a surfactant, is easily absorbed on the surface of MNBs and can be collected together with the microplastic pollution. Our research has demonstrated that the MNB technique could be promising for use in microplastic recycling and reducing detergent pollution in daily life.

Synergistic solubilization of phenanthrene using micro-nanobubbles and cationic surfactants: Universal verifying, amplifying, and strengthening the synergy

Micro-nanobubbles (MNBs) with their negatively charged surface and cationic surfactant with a positively charged hydrophilic head were designed to synergistically solubilize polycyclic aromatic hydrocarbons (PAHs). Through response surface method experimentation, the results showed that MNBs had no obvious solubilizing effect for the PAH, phenanthrene. However, MNBs and the cationic surfactant didodecyldimethylammonium bromide (DDAB) had a synergistic solubilization effect on phenanthrene. Through the analysis of physical and chemical factors, it could be inferred that the synergy was caused by a conversion in the structure of the vesicles formed by DDAB after the combination of DDAB and MNBs. This structure conversion improved the phenanthrene solubility. In addition to being amplified, this synergy was verified to be universal and could be strengthened. The synergy, which increased with increasing DDAB and MNB concentrations, could achieve up to about 3 times the solubilizing as that without MNBs. In addition to DDAB, MNBs could also synergistically solubilize phenanthrene with other cationic surfactants. Changing the gas source of MNBs from air to nitrogen or oxygen could increase the negative surface charge, which enhanced the synergistic effect between MNBs and cationic surfactants. These results demonstrate a novel method for synergistic solubilization of PAHs by surfactant and MNBs while it can decrease the excessive use of surfactants causing the pollution issues. The synergistic effect between cationic surfactants and MNBs has the potential to be widely used in environmental and medical fields.

Oxidative leaching of sandstone uranium ore assisted by ozone micro-nano bubbles

Oxidative leaching of sandstone uranium ore assisted by ozone micro-nano bubbles

Polishing of zirconia ceramics by chemically-induced micro-nano bubbles

This study introduces micro-nano bubbles (MNBs) in the process of polishing zirconia ceramics through sodium borohydride hydrolysis to assist in polishing yttria-stabilized zirconia (YSZ). Compared with conventional silica sol, the material removal rate using this MNB-assisted technology is increased by 261.4%, and a lower surface roughness of 1.28 nm can be obtained. Raman, X-ray diffraction, and X-ray photoelectron spectroscopy are used to study the structural changes and phase stability of the YSZ during different polishing periods. The results show that MNBs are the key factor promoting the transformation from the tetragonal phase to the monoclinic phase on the surface of the YSZ during polishing. The H2O molecules (or OH− ions) on the surface of the YSZ are driven by the thermal kinetic energy of the micro-jets formed by the collapse of micro-bubbles, and they permeate to occupy more oxygen vacancies in the crystal lattice. Atomic force microscopy and nano-indentation tests show that the micro-protrusions on the surface of the YSZ preferentially undergo phase transformation, and their hardness decreases. This promotes abrasives to preferentially remove rough spots on the surface and achieve more efficient polishing. We believe this work adds valuable insights regarding low-temperature degradation and ultra-precise machining of YSZ ceramic materials.

Oxidation of Congo red by Fenton coupled with micro and nanobubbles

ABSTRACT Dye wastewater is a kind of refractory organic wastewater. Fenton coupled with micro-nano bubbles (MNBs+FT) was used for the degradation of Congo red (CR), aiming at simplifying the organic pollutants degradation process and reducing the cost of the process. The optimum condition of Fenton alone, the outlet pressure of the cavitation process and different combinations on the degradation of CR dye wastewater were discussed in this study. The results showed that the degradation of CR (100 mg/L) could reach 94.4% by using the MNBs+FT at the pH of 7, which was 72% higher than that using Fenton oxidation alone and 79% higher than that using MNBs alone. Based on the same degradation efficiency, the traditional Fenton process alone required 8 times the dose of oxidants of these combination systems, and the synergy coefficient of MNBs+FT was up to 2.44. ESR analysis indicated that ·OH was the predominant active species during the degradation of CR and MNBs+FT improved the utilization efficiency of H2O2 and produced more ·OH. Besides, the MNBs+FT could extend the pH range of the high-efficiency oxidation reaction, and it could also keep a high degradation rate under neutral conditions, which eliminated the process of adjusting the pH and reduced the anti-corrosion requirements of the equipment. According to the economic analysis results, the total cost of treatment for the MNBs/FT was about 13% of the cost of only the Fenton process. This study provides a reference for the application of MNBs+FT systems in full-scale dye wastewater treatment.

Nano-Oxy: Diabetic ulcer treatment using oxygen nanoparticles concept as innovation in reducing amputation rates and antibiotics usage

Diabetes mellitus is a metabolic disease characterized by chronic hyperglycemia caused by defects in insulin secretion, insulin reactions, or both. More than one third of diabetic patients have complications in the form of diabetic ulcers, and half are infected, and 15% of these infections require limb amputation. High cost expenditure and risks of microbial resistance to antibiotics also adds the complexity of the problem. The purpose of this literature review is to offer Nano-Oxy, using oxygen in nanoparticle size, as an alternative diabetic ulcer treatment. Literature searching was conducted through online search method. Oxygen therapy has been widely used to treat diabetic ulcers, including hyperbaric oxygen therapy (HOT) and topical oxygen therapy (TOT). Both of them have good results on diabetic ulcer therapy. Oxygen can act as an antimicrobial agent through the activation mechanism of neutrophils and macrophages which play a role in phagocytosis process and ROS regeneration. Nano-Oxy has advantages than the previous therapy, such as it does not cause barotrauma, oxygen poisoning, and low risk of burning. The mechanism of how Nano-Oxy works is similar with the Micro-nanobubbles (MNBs) concept. The negatively charged surface of MNBs can prevent them from aggregating, attracts particles, and help remove debris. MNBs also generate free radicals while shrinking in water, which contribute to its antibacterial effect. In addition, Nano-oxygen technology can be applied externally, but still have effect on the intended target cells. Therefore, Nano-oxygen can be used as a diabetic ulcer therapy to replace the role of antibiotics.

A Novel Technique Using Advanced Oxidation Process (UV-C/H2O2) Combined with Micro-Nano Bubbles on Decontamination, Seed Viability, and Enhancing Phytonutrients of Roselle Microgreens

Microbial contamination commonly occurs in microgreens due to contaminated seeds. This study investigated the decontamination effects of water wash (control), 5% hydrogen peroxide (H2O2), UV-C (36 watts), advanced oxidation process (AOP; H2O2 + UV-C), and improved AOP by combination with microbubbles (MBs; H2O2 + MBs and H2O2 + UV-C + MBs) on microbial loads, seeds’ viability, and physio-biochemical properties of microgreens from corresponding roselle seeds. Results showed that H2O2 and AOP, with and without MBs, significantly reduced total aerobic bacteria, coliforms, Escherichia coli (E. coli), and molds and yeast log count in seeds as compared to the control. Improved AOP treatment of H2O2 + UV-C + MBs significantly augmented antimicrobial activity against total bacteria and E. coli (not detected,) as compared to control and other treatments due to the formation of the highest hydroxy radicals (5.25 × 10−13 M). Additionally, H2O2 and combined treatments promoted seed germination, improved microbiological quality, total phenolic, flavonoids, and 2,2-diphenyl-1-picrylhydrazyl radical (DPPH•) activity of the grown microgreens. Ascorbic acid content was induced only in microgreens developed from H2O2-treated seeds. Single UV-C treatment was ineffective to inactivate the detected microorganism population in seeds. These findings demonstrated that improved AOP treatment (H2O2 + UV-C + MBs) could potentially be used as a new disinfection technology for seed treatment in microgreens production.

Degradation of Tetracycline in Wastewater by Persulfate Activated with Micro-Nano Bubbles

Degradation of Tetracycline in Wastewater by Persulfate Activated with Micro-Nano Bubbles