Search Results (5)

Wastewater generation is a growing concern in the preliminary treatment of heavy crude oil and tar sand. The separation of fine oil droplets from water by flotation is a critical process in the production of bitumen from tar sand. The flow structure from a high-resolution simulation of a single air macrobubble (>3 mm diameter) rising through water in the presence of a very dilute dispersion of mono-sized oil microdroplets (30 μm) under quiescent conditions is presented. A combined model of computational fluid dynamics (CFD), a volume of fluid (VOF) multiphase approach, and the discrete phase method (DPM) was developed to simulate bubble dynamics, the trajectories of the dispersed oil droplet, and the interaction between the air bubble and the oil droplet in quiescent water. The CFD–VOF–DPM combined model reproduced the interacting dynamics of the bubble and oil droplets in water at the bubble–droplet scale. With an extremely large diameter ratio between the bubble and the dispersed oil droplet, this model clearly demonstrated that the dominant mechanism for the interaction was the hydrodynamic capture of oil droplets in the wake of a rising air macrobubble. The entrainment of the oil droplets into the wake of the rising bubbles was strongly influenced by the bubble’s shape. Full article

Micro- and nanobubbles are tiny gas bubbles that are smaller than 100 μm and 1 μm, respectively. This study investigated the impact of electric field ozone nanobubbles (EF-ONBs) on the purification of both deionised and aquaculture water bodies, finding that heightened reactive oxygen species (ROS) production and oxygen reduction potential (ORP) are correlated to a higher production of EF-ONBs. In particular, it was found that there were substantially reduced ultraviolet light requirements for aquaculture when using EF-ONBs to maintain aquaculture purification standards. It is clear that the approximately exponential decay is slowed down by almost ten times by EF-ONBs even without UV applied, and that it is still roughly six times longer than the ‘control’ case of standard O₃ sparging in water (i.e., meso- and macro-bubbles with no meaningful level of dispersed-phase, bubble-mediated dissolution beyond the standard Henry’s law state—owing mostly to rapid Stokes’ law rising speeds). This has very positive implications for, inter alia, recirculation aeration systems featuring an ozonation cycle, as well as indoor agriculture under controlled-light environments and malting, where ozonation cycles are also often used or contemplated in process redesign strategies. Such promising results for EF-ONBs offer, inter alia, more sustainable aquaculture, water sterilisation, indoor farming, and malting. Full article

Ozone (O₃) has been widely used for water and wastewater treatment due to its strong oxidation ability, however, the utilization efficiency of O₃ is constrained by its low solubility and short half-life during the treatment process. Thereby, an integrated approach using novel nanobubble technology and ozone oxidation method was studied in order to enhance the ozonization of ammonia. Artificial wastewater (AW) with an initial concentration of 1600 mg/L ammonia was used in this study. In the ozone-nanobubble treatment group, the concentration of nano-sized bubbles was 2.2 × 10⁷ particles/mL, and the bubbles with <200 nm diameter were 14 times higher than those in the ozone-macrobubble treatment control group. Ozone aeration was operated for 5 min in both nanobubble treatment and control groups, however, the sampling and measurement were conducted for 30 min to compare the utilization of O₃ for ammonia oxidation. H⁺ was the by-product of the ammonia ozonation process, thus the pH decreased from 8 to 7 and 7.5 in nanobubble treatment and control groups, respectively, after 30 min of operation. The fast removal of ammonia was observed in both systems in the first 10 min, where the concentration of ammonia decreased from 1600 mg/L to 835 and 1110 mg/L in nanobubble treatment and control groups, respectively. In the nanobubble treatment group, ammonia concentrations kept the fast-decreasing trend and reached the final removal performance of 82.5% at the end of the experiment, which was significantly higher than that (44.2%) in the control group. Moreover, the first-order kinetic model could be used to describe the removal processes and revealed a significantly higher kinetic rate constant (0.064 min⁻¹) compared with that (0.017 min⁻¹) in the control group. With these results, our study highlights the viability of the proposed integrated approach to enhance the ozonation of a high level of ammonia in contaminated water. Full article

Beverage industries often discharge large amounts of organic matter with their wastewater. Purification of the effluent is their obligation, but it is nontrivial. Among wastewater components, removal of dissolved organic matter often requires much effort. Therefore, a special effective technique must be considered. Microbubbles (1–100 μm) have several special properties of relevance to wastewater treatment. In this study, the effectiveness of microbubbles for treating and purifying beverage wastewater was evaluated. Orange juice, lactic acid drink, and milk were used as model substrates of dissolved organic matter, and degradation experiments were carried out. Rates of air supply by microbubbles were 0.05% (air/wastewater) min⁻¹. Results indicated that the total organic carbon (TOC) in an experimental vessel containing milk (high nitrogen content) decreased by 93.1% from 11.0 to 0.76 g during a 10-day incubation. The TOC of lactic acid drink (least nitrogen content) decreased by 66.3%, from 15.6 to 5.26 g, and the TOC of orange juice (medium nitrogen content) decreased by 82.7%, from 14.8 to 2.55 g. Large amounts of particulate organic matter floated on the water surface in the milk with microbubbles and were removed easily, while almost no floating materials were observed in the orange juice and lactic acid drink. In contrast, in the macrobubble treatment (diameter 0.1 to 2 mm), only 37.0% of TOC in the milk was removed. Whereas the macrobubble treatments were anaerobic throughout the incubations, the microbubble treatments returned to aerobic conditions quickly, and brought 10 times greater bacterial abundances (>10⁸ cells mL⁻¹). These results suggest that microbubbles are much superior to macrobubbles in supplying oxygen and accelerating the growth of aerobic bacteria, and that wastewater containing more nitrogenous compounds was purified more effectively than that with less nitrogen by microbial degradation and floating separation. Full article

A novel auto-aspirated sparger is examined experimentally in a closed-loop reactor (CLR) at lab scale using particle image velocimetry, high-speed camera and oxygen mass transfer rate measurements. State-of-the-art 3D printing technology was utilized to develop the sparger design in stainless steel. An insignificant change in the bubble size distribution was observed along the aerated flow, proving the existence of a low coalescence rate in the constraint domain of the CLR pipeline. The studied sparger created macrobubbles evenly dispersed in space. In pure water, the produced bubble size distribution from 190 to 2500 μm is controlled by liquid flow rate. The bubble size dynamics exhibited a power-law function of water flow rate approaching a stable minimum bubble size, which was attributed to the ratio of the fast-growing energy of the bubble surface tension over the kinetic energy of the stream. Potentially, the stream energy can efficiently disperse higher gas flow rates. The oxygen transfer rate was rapid and depended on the water flow rate. The aeration efficiency below 0.4 kW/m³ was superior to the commonly used aerating apparatuses tested at lab scale. The efficient gas dissolution technology has potential in water treatment and carbon capture processes applications. Full article