Prediction and Experimental Study of Mass Transfer Properties of Micronanobubbles

Nanobubbles produced by nanopores to probe gas-liquid mass transfer characteristics

HYPOTHESIS

This study tested the hypothesis of how the nanopore size of membranes and how the surface charge of nanobubbles responds to its pinch-off from the nanopore. This study also tested the hypothesis that nanobubbles that remain in solution after production may increase the dissolved oxygen content in water.

EXPERIMENTS

The effect of membrane pore size, hydrodynamic conditions (gas and liquid flow rates), and physicochemical parameters (pH and temperature) on volumetric mass transfer coefficient (kLa) for oxygen nanobubbles formed by the nanopore diffusion technique was investigated. This study experimentally determined the kLa by carefully removing the dissolved oxygen by nitrogen purging from nanobubble suspension to examine the sole contribution of nanobubble dissolution in water to the reaeration.

RESULTS

Scaling estimates indicate that the nanobubble pinch-off radius and nanopore radius have a power-law correlation and that nanobubble size declines with the nanopore size. This is in line with our experimental results. The surface charge of nanobubbles delays its pinch-off at the gas-liquid interface. Nanobubbles offered 3-4 times higher kLa than microbubbles. Standard oxygen transfer efficiency in water was found to be 78%, significantly higher than that in microbubbles. However, dissolving stable nanobubbles in water does not considerably increase dissolved oxygen levels.

Effect of nanobubbles on the mobilization of microplastics in shorelines subject to seawater infiltration

The widespread presence of microplastics (MPs) in the ocean has varying degrees of impact on ecosystems and even human health. Coastal tidal zones are crucial in controlling the movement of MPs, which are influenced by waves and tidal forces. Meanwhile, natural nanobubbles (NBs) in the ocean can affect the hydrodynamic properties of the tidal zone. The mobilization of MPs in coastal tidal zones under the effect of NBs has been less studied. In this study, we explored natural NBs' influence on the mobilization of MPs in shorelines subject to seawater infiltration. Using glass beads as a substrate, a coastal porous environment was constructed through column experiments, and the pump-controlled water flow was used to study the transport of MPs subject to seawater movement within the substrate. The infiltration of MPs under continuous and transient conditions, as well as the upward transport induced by flood tide, were considered. The role of salinity in the interactions between NBs, MPs, and substrates was evaluated. Salinity altered the energy barriers between particles, which in turn affected the movement of MPs within the substrate. In addition, hydrophilic MPs were more likely to infiltrate within the substrate and had different movement patterns under continuous and transient flow conditions. The motion of the MPs within the substrate varied with flow rate, and NBs limited the vertical movement of MPs in the tidal zone. It was also observed that NBs adsorbed readily onto substrates, altering the surface properties of substrates, particularly their ability to attach and detach from other substances.

Effect of Micro-Nano Bubble Water and Silica Fume on Properties of C60 Concrete

Micro-nano bubble water (WNBW) in concrete is relatively uncommon due to its newness as a technology. This paper presents the preparation of C60 concrete with 35% fly ash (FA) through WNBW and varying amounts of silica fume (0%, 4%, 7%, and 10% SF). The study examines the impact of WNBW and SF on the working performance, compressive strength, and durability of concrete. The findings indicate that applying WNBW and SF independently or jointly deteriorates the working performance of fresh concrete. However, compared to regular mixing water, WNBW reduces the concrete passing time through the V-funnel, decreasing by 40%, 39.1%, 42.9%, and 50.5% for the four varying SF contents. Furthermore, using WNBW, SF, or both resulted in the increased compressive strength of concrete at 7 days and 28 days, with 7% SF content yielding a 12.2% and 6.6% increase, respectively. Using a combination of WNBW and SF has been shown to decrease the impermeability of concrete effectively. The addition of 4% SF results in the lowest electric flux when using regular mixing water, with a discernible decrease of 30.1% compared to the control group. Conversely, using WNBW as mixing water yields a decrease in electric flux at each SF content, with the maximum decrease being 39.7%. Furthermore, both the single and combined use of these materials can contribute to the reduction in the carbonation resistance of the concrete. C60 concrete mixed with 7% SF and 100% WNBW boasts enhanced frost resistance, as indicated by the mass loss and dynamic elastic modulus loss being the least following freeze-thaw under the same SF content. According to the findings of the tests, there is evidence that the incorporation of 7% SF and 100% WNBW into C60 concrete results in lowered viscosity, a highly advantageous attribute for actual construction. Additionally, this mixture displays impressive compressive strength and durability properties. These results provide technical support regarding the integration of WNBW and SF in C60 concrete.

A comparative study of removal efficiency of organic contaminant in landfill leachate-contaminated groundwater under micro-nano-bubble and common bubble aeration

Landfill leachate-contaminated groundwater is widespread all over the world. In order to study the organic contaminant removal efficiency of landfill leachate-contaminated groundwater under oxygen micro-nano-bubble (MNB) aeration, a series of lab-scale experiments of oxygen MNB aeration as well as common bubble (CB) aeration were conducted. Firstly, the difference in mass transfer, microbial activity enhancement, and contaminant removal efficiency between MNB and CB aeration was estimated. Then, the composition variations of dissolved organic matter (DOM) in groundwater treated by MNB or CB aeration were characterized by ultraviolet-visible (UV-VIS) absorption spectrum and fluorescence excitation-emission matrix (EEM). The test results showed that the oxygen utilization efficiency and volumetric oxygen transfer coefficient of MNB aeration were 10 and 50 times that of oxygen CB aeration, respectively. On the 30th day after MNB aeration, the dehydrogenase activity (DHA) of groundwater increased by 101.25%. Compared with CB aeration, the chemical oxygen demand (COD), 5-day biochemical oxygen demand (BOD₅), and ammonia nitrogen removal efficiency under MNB aeration increased by 29.72%, 13.43%, and 138.59%, respectively. With the biodegradation effect of MNB aeration, a large number of protein-like and soluble microbial by-product substances were degraded, and humic and fulvic acid-like substances were degraded to a certain level. Oxygen MNB aeration played a chemical oxidation effect while enhancing the biodegradation of groundwater, and it was an energy-efficient landfill leachate-contaminated groundwater treatment method.