Coarse Bubble Research Articles

Coarse bubble mixing in anoxic zone greatly stimulates nitrous oxide emissions from biological nitrogen removal process

The biological nitrogen removal process in wastewater treatment inevitably produces nitrous oxide (N2O), a potent greenhouse gas. Coarse bubble mixing is widely employed in wastewater treatment processes to mix anoxic tanks; however, its impacts on N2O emissions are rarely reported. This study investigates the effects of coarse bubble mixing on N2O emissions in a pilot-scale mainstream nitrite shunt reactor over a 50-day steady-state period. Online and offline N2O monitoring campaigns show that coarse bubble mixing in the anoxic zones significantly elevates N2O emissions, yielding an extremely high emission factor of 15.5 ± 3.5 %. Intensive sampling and isotopic analyses suggest that the elevated emissions are primarily due to the inhibition of the N2O denitrification process by oxygen in the anoxic phase introduced by coarse bubbling. Substituting coarse bubble mixing with submersible pump mixing resulted in a substantial reduction of N2O emissions, decreasing the emission factor by an order of magnitude to 1.2 ± 0.8 %. The findings reveal that a previously overlooked factor, coarse bubble mixing, can significantly stimulate N2O emissions. The use of coarse bubble mixing in anoxic tanks of biological nitrogen removal warrants caution.

The role of microbubble dose in combined microflotation of fine particles

Flotation of small particles is one of the global challenges facing the mineral raw materials processing industry. Large amounts of non-ferrous and rare metals are lost in the flotation tailings in the form of mineral particles below 15 µm in size as a result of the low effectiveness of their capture by coarse bubbles generated in conventional flotation machines. The method of combined microflotation, developed in recent years, uses conventional coarse bubbles (CB) and microbubbles (MB) produced in the stand-alone generator of air-in-water microdispersion, which serves as the flotation carriers. Depending on the MB dose, the effect of their application may be positive or negative. The theoretical analysis of various mechanisms of particle transfer onto the surface of coarse bubbles and further into the froth layer allowed to obtain the formula for the optimal MB dose f=d<sub>d</sub>/2d<sub>p</sub>r<sub>p</sub>, where d<sub>d</sub> is MB size; d<sub>p</sub> and r<sub>p</sub> respectively are the size and the density of particles. Experiments performed on the copper ore flotation tailings at the Atalaya Mining (Spain) and Chaarat Kapan (Armenia) concentrators showed that, besides the optimal MB dose in the range of 1-3 ml/g, there is another optimal MB dose in the range of 10-20 ml/g, where the copper recovery increases by several percent compared to the reference test (f = 0). The deep minimum in copper recovery is observed in the area between the optimal MB doses, which is by several percent lower than the value in the reference test.

Impacts of micron-sized aeration bubble on sludge properties and hydraulic dynamics in relation to membrane fouling alleviation

This investigation elucidates the influence of micron-scale aeration bubbles on the improvement of anti-fouling characteristics within submerged membrane bioreactors (sMBRs). A systematic examination of sludge properties, hydraulic dynamics, and fouling tendencies revealed that the application of microbubble aeration, specifically at dimensions of 100 μm, 80 μm, and 30 μm, significantly reduced sludge electrostatic repulsion and augmented particle size distribution, as opposed to the utilization of coarse bubble aeration of 1 mm. Notably, the employment of 100 μm bubbles achieved a significant reduction in the proportion of smaller particles (<10 μm) and sludge viscosity, thereby facilitating a more homogenous and vigorous turbulence at the membrane interface. These optimized conditions were instrumental in the substantial reduction of membrane fouling, which was corroborated by the diminished rate of fouling, reduced resistance accumulation, and lesser foulant deposition. The investigation identified sludge particle size, turbulent kinetic energy, and shear stress as the predominant factors influencing the development of membrane fouling. The findings underscore the pronounced advantages of employing 100 μm-sized bubbles in aeration strategies, providing enhanced understanding for the optimization of aeration parameters to improve sMBR efficiency and maintenance.

Retained intracardiac air in cardiovascular surgery: a re-visited problem.

Intracardiac air remains an unsolved problem in the realm of cardiac surgery, leading to embolic events encompassing conduction disturbance, heart failure, and stroke. Transesophageal echocardiography allows the visualization of three distinct types of retained intracardiac air: pooled air, coarse bubbles, and microbubbles. The former two predominantly manifest in the right upper pulmonary vein, left atrium, and left ventricle, exhibiting passive movement along the vessel walls by buoyancy. De-airing, involving "eradication" of air from circulation and "expulsion" of air from the heart into the systemic circulation assumes paramount importance in averting embolic events. Optimal de-airing strategies necessitate the thorough elimination of air during the static phase before the resumption of cardiac activity, achieved through aspiration or guided exit leveraging buoyancy. While the dynamic phase, characterized by active cardiac beating, presents challenges for air eradication, the majority of air expulsion occurs towards the aorta during this period. In this latter phase, collaborative efforts among the surgeon, anesthesiologist, and clinical engineer are pivotal to mitigate the risk of bolus air embolism. The efficacy of carbon dioxide insufflation is limited, as it is rapidly aspirated by wall suction or absorbed into the bloodstream. Consequently, the "air" identified by TEE is acknowledged as conventional air. Understanding the distinctive properties of air as well as timely and judicious collaboration for detection and removal, with the ultimate goal of eradication, emerges as an essential prerequisite for successful de-airing in the evolving era of cardiac surgery.

Employing low dissolved oxygen strategy to simultaneously improve nutrient removal, mitigate membrane fouling, and reduce energy consumption in an AAO-MBR system: Fine bubble or coarse bubble?

The high energy consumption associated with aeration, which is a widely used hydrodynamic method to mitigate membrane fouling in membrane bioreactors (MBR), poses a significant challenge to the widespread application of aerated MBR. In this study, low dissolved oxygen was applied to optimize the overall performance and reduce energy consumption in an anaerobic-anoxic-aerobic MBR (AAO-MBR) under fine and coarse bubble aeration conditions. Coarse bubble aeration exhibited better membrane fouling control, but induced releasing more proteins and polysaccharides in mixed liquor than that in fine bubble aeration. Coarse bubble aeration resulted in a decrease in the relative abundance of function bacteria, and there was a corresponding drop in enzymes involved in the nitrogen and phosphorus pathways. Furthermore, the average total specific energy demand (0.45 ± 0.02 kW·h/d) and total carbon emissions (0.32 ± 0.01 kg/d) of coarse bubble aeration was remarkably higher than that of fine bubble aeration (0.35 ± 0.01 kW·h/d and 0.25 ± 0.02 kg/d). Our results demonstrate that the fine bubble aeration in low dissolved oxygen-based AAO-MBR can optimize the overall performance and reduce energy consumption, thereby making it a more viable option for the wastewater treatment.

Ozone micron bubble pretreatment for antibiotic resistance genes reduction in hospital wastewater treatment

Ozone micron bubble (OMB) treatment offers a promising approach to effectively eliminate Antibiotic Resistance Genes (ARGs) from infectious medical wastewater and mitigate the threat of drug resistance transmission. This study evaluated the effectiveness of OMB treatment for reducing ARGs from infectious medical wastewater in laboratory and on-site pilot treatment setups. In part, the presence of antibiotic residues in a hospital wastewater treatment plant (WWTP) and the impact of hospital wastewater on the distribution of ARGs in a wastewater collection system were also investigated. The results of wastewater collection system survey revealed a high prevalence of ARGs in the system, particularly mcr-1, largely originating from medical wastewater discharges. Furthermore, analysis of antibiotic residues in the hospital wastewater treatment system showed significant accumulation, particularly of quinolone antibiotics, in the biomass of the biological oxidation tank, suggesting a potential risk of ARG proliferation within the system. Comparison of wastewater samples from domestic and hospital WWTPs revealed a relatively higher abundance of ARGs in the latter, with differences ranging from 2.2 to sixfold between corresponding locations in the treatment plants. Notably, the biological oxidation unit of both WWTPs exhibited a greater proportion of ARGs among all sampled points, indicating the potential proliferation of ARGs within the biomass of the treatment units. ARG degradation experiments showed that OMB treatment resulted in a significantly lower CT value (9.3 mg O3 L−1 min) compared to ozone coarse bubble treatment (102 mg O3 L−1 min) under identical test conditions. Moreover, the use of OMB on site significantly reduced the accumulation of ARGs in hospital wastewater, underscoring its potential as an effective solution for mitigating ARG spread.

Analyzing the effects of different patterns of diffuser layouts on air distribution and mixing quality in an aeration tank using CFD

A diffused aeration system in an activated sludge process is generally designed based on a limited number of typical diffuser patterns. There are instances where these patterns have shown various operational and process issues, resulting in poor process performance. To address these issues, bubble interactions and the mixing conditions must be factored into the design of alternative patterns. For this purpose, a validated full-scale CFD model was used to simulate five diffuser patterns: lateral, grid, line, stripe, and checkered patterns‎, the first two in operation, and the next three as designed patterns. The patterns were simulated for an aeration tank under identical functional conditions. The population balance method was incorporated into the model to analyze how various patterns affect bubble size distribution. It was found that changing the pattern of diffusers had a significant effect on bubble breakup/coalescence and the resulting bubble size distribution. The results showed a range of 6.1–22.9% for the coarse bubble percentage and 11.9–16% for the fine bubble percentage in the five simulated patterns. Moreover, evaluating flow circulation and velocity based on the average flow velocity data of the simulated patterns showed up to 30% variation, ranging from 0.29 to 0.375 m/s. It highlighted the great impact of diffuser patterns on bubble size and mixing quality as notable factors in oxygen transfer efficiency. Finally, the proposed patterns were compared and ranked based on air distribution, bubble size, and mixing quality criteria using the multi-criteria decision-making (MCDM) approach. It was concluded that the checkered pattern outperformed the proposed and existing ones.

Influence of discontinuous on-line ultrasonic irradiation applied in ultrafiltration MBR systems over the physical-chemical and biological characteristics of the activated sludge

The influence of ultrasound (US) irradiation applied for membrane fouling control of a membrane bioreactor (MBR) over the physico-chemical and biological characteristics of the activated sludge was analysed. Three parallel MBR modules coupled to a sonicator which provided US irradiation at 20, 30 and 40kHz (fixed power 0.5W/L) were evaluated. The modules were fed with activated sludge from a conventional MBR. Particle size distribution (PSD), exopolysaccharide substances, soluble microbial products, biomass concentration and kinetic and stoichiometric parameters were assessed. The combination of 2s US pulses every 3min of filtration with 1min of backwashing with 3s of coarse bubble aeration achieved good results in membrane fouling control. A slight worsening of the effluent quality was observed for the sonicated MBR modules with respect to a conventional MBR, mainly for the 20kHz module, which showed the worst transmembrane pressure control. A slight activated sludge PSD displacement towards larger sizes was observed for all frequencies, but the characteristics of the activated sludge was not significantly altered, so the worsening of the effluent quality or membrane fouling were not related to the effect of US irradiation on biomass. Alteration in the biological activity was not relevant.

The impact of solid/floc holdup on oxygen transfer in a rotating hollow fiber membrane bioreactor under endogenous conditions.

A set of oxygen transfer experiments in clean water and three different activated sludge concentrations were conducted with fine and coarse bubble aeration in a rotating hollow fiber membrane bioreactor to observe the impact of different rotational speeds on the oxygen transfer rate. The results showed that with increasing membrane rotational speed, the oxygen transfer coefficient enhanced while the α-factor showed similar values at comparable sludge concentrations and solid/floc holdups. The highest improvement rates occurred during the experiments with coarse bubble aeration at 50 rpm and the lowest specific airflow rate. The solid/floc holdup appears to universally impact oxygen transfer depletion regardless of what reactor type, diffuser setup and membrane rotational speed were used in the wastewater experiments.

Column rougher flotation of fine niobium-bearing particles assisted with micro and nanobubbles

Rougher column flotation pilot plant (80 kg h−1 of solids) studies, recovering pyrochlore (fine and ultrafine samples), compared separation parameters with and without the injection of nano and microbubbles. An aqueous dispersion of those bubbles, generated in a surfactant solution using a centrifugal multiphase pump coupled to a needle valve, was added to the column cell as dilution water (0.1 m3 h−1), after the conditioning stage. The results showed that, for the fine sample (D32 = 15 µm; D50 = 38 µm and about 5–5.8 % Nb2O5 feed grade), the injection of micro and nanobubbles enhanced the Nb2O5 recovery by 1.4% at similar concentrate grades. For the ultrafine and poorer feed grade sample (D32 = 1.5 µm; D50 = 4 µm and 1.9–2.3 % Nb2O5 feed grade), the flotation efficiency was higher, increasing the Nb2O5 recovery by about 4.8% while improving the concentrate grade by 30%(enrichment ratios varying from 5.2 to 6.6). The results are explained by the interfacial mechanisms involving the enhanced capture of particles by a combination of nano (30–800 nm diameter), micro (30–100 µm diameter), and coarse bubbles (>600 µm diameter). This appears to confirm the multi-sized bubbles concept and importance in flotation whereby the finest bubbles seem to attach rapidly to the pyrochlore particles acting as “seeds” for the coarser bubbles to adhere. This alternative was proved at high flow-rate pilot scale in long trials, permitting to conclude its high potential in the recovery of fine and ultrafine minerals by flotation, especially in these valuable low grade niobium-bearing particles.

A Review of Bubble Aeration in Biofilter to Reduce Total Ammonia Nitrogen of Recirculating Aquaculture System

Aeration becomes an essential aspect of biofilter performance to reduce ammonia nitrogen in the Recirculating Aquaculture System (RAS). Efficient aeration introduces air into water media and offers an aerobic environment in the biofilter for microbial degradation of organic matter and ammonia nitrogen. The efficiency of the bubble aeration depends on the size of the bubbles; these include coarse bubble, microbubble, fine bubble, and ultrafine bubble or nanobubble. This review highlights an overview of bubble aeration features in a biofilter to reduce ammonia nitrogen. Moreover, key aspects responsible for the ammonia nitrogen removal efficiencies, such as oxygen transfer, microbial community, and biofilm thickness, are evaluated in this review. In conclusion, the bubble size of aeration affects the microbial community of nitrifying bacteria, consequently determining the growth and thickness of biofilm to improve ammonia removal efficiency. It is emphasized that fine bubble and nanobubble aeration have very positive prospects on improving biofilter performance, though they are currently not widely used in RAS.

Aeration model for submerged membrane bioreactor – Characterization, oxygen transfer rate, pollutant removal, and energy consumption

The present study uses the Activated Sludge Model-1 and Hydromantis GPS-X modelling software to develop an aeration model for a submerged membrane bioreactor. PVDF membranes with an individual surface area of 10 m2 are used for the experiments. The Activated Sludge Model-1 method investigates the coarser and fine bubble aeration (FBA) systems. According to the study, the FBA system produced significantly better oxygen transfer efficiency and used considerably less energy to perform. The effect of fine and coarse bubble aeration on oxygen transfer efficiency study shows that fine bubble aeration produced 2.1 kg O2/kWh, which is higher than coarse bubble aeration 1.5 kg O2/kWh. The pollutant removal efficiency based on fine bubble aeration shows that the COD, BOD, TN, and TSS removal is obtained at around 93.97%, 96.61%, 95.30%, and 99.70%, respectively. According to the energy consumption assessment, FBA needed 135 kWh/m3, and coarse bubble aeration required 230 kWh/m3, representing 26.21% and 44.66%, of energy requirement, respectively. According to the experimental results, coarse bubbles needed 18.45% more energy for the same permeation. Furthermore, the influence of fine and coarse bubble aeration on membrane fouling found that membrane in FBA systems are less prone to fouling than in coarse bubble aeration systems.

Biological treatment of municipal wastewater using fixed rope media technology: Impact of aeration scheme

This paper characterized a new fixed rope media system to upgrade decentralized and small-scale wastewater treatment plants. A primary effluent of municipal wastewater was treated using two pilot-scale reactors equipped with full-scale sized fixed rope media technology, one of the reactors was aerated using a coarse bubble tube and the other using a custom fine bubble aeration system. The study examined the impact of the aeration scheme and intensities and the COD/NH 3 -N ratio on ammonia and COD removal rates, excessive biofilm growth, slough-off, and microbial communities’ composition. The average biofilm ammonia and COD removal rates ranged from 0.23 ± 0.15 to 0.38 ± 0.26 gNH 3 -N/m 2 .d and 1.35 ± 0.95 to 3.05 ± 1.21 gCOD/m 2 .d, respectively. The fine and coarse bubble reactors showed comparable carbon oxidation rates; however, the fine bubble reactor showed a higher nitrification rate than the coarse bubble reactor at lower aeration intensities despite the similar dissolved oxygen concentration. Correspondingly, an increase in COD/NH 3 -N and excessive biofilm growth decreased the NH 3 -N removal performance but did not affect the COD removal efficiency. Further analysis of the microbial communities composition revealed that the reactors supported a relatively substantial amount of AOB (55 and 63%) and denitrifying bacteria (36 and 21%) with a relatively lower NOB (7 and 8%) and anammox (1 and 8%) species in the fine and coarse bubble aeration reactors, respectively. Overall this study demonstrated the feasibility of one stage fixed rope media to treat COD and ammonia and meet treatment objectives, thus providing an alternative solution to decentralized and smaller plant upgrades. • Ammonia and COD removal efficiency of innovative fixed rope media technology was evaluated. • Different aeration schemes showed minimal impact on the DO concentration but impacted removal performances. • C/N ratio influenced NH 3 -N removal but not COD removal. • Slough off did not impact COD removal; however, it enhanced ammonia removal. • Reactor with the fine bubble aeration supported a relatively higher fraction of denitrifying bacteria.

Mass Transfer, Gas Holdup, and Kinetic Models of Batch and Continuous Fermentation in a Novel Rectangular Dynamic Membrane Airlift Bioreactor

Compared with conventional cylinder airlift bioreactors (CCABs) that produce coarse bubbles, a novel rectangular dynamic membrane airlift bioreactor (RDMAB) developed in our lab produces fine bubbles to enhance the volumetric oxygen mass transfer coefficient (kLa) and gas holdup, as well as improve the bioprocess in a bioreactor. In this study, we compared mass transfer, gas holdup, and batch and continuous fermentation for RNA production in CCAB and RDMAB. In addition, unstructured kinetic models for microbial growth, substrate utilization, and RNA formation were established. In batch fermentation, biomass, RNA yield, and substrate utilization in the RDMAB were higher than those in the CCAB, which indicates that dynamic membrane aeration produced a high kLa by fine bubbles; a higher kLa is more beneficial to aerobic fermentation. The starting time of continuous fermentation in the RDMAB was 20 h earlier than that in the CCAB, which greatly improved the biological process. During continuous fermentation, maintaining the same dissolved oxygen level and a constant dilution rate, the biomass accumulation and RNA concentration in the RDMAB were 9.71% and 11.15% higher than those in the CCAB, respectively. Finally, the dilution rate of RDMAB was 16.7% higher than that of CCAB during continuous fermentation while maintaining the same air aeration. In summary, RDMAB is more suitable for continuous fermentation processes. Developing new aeration and structural geometry in airlift bioreactors to enhance kLa and gas holdup is becoming increasingly important to improve bioprocesses in a bioreactor.

Effect of air nanobubbles on oxygen transfer, oxygen uptake, and diversity of aerobic microbial consortium in activated sludge reactors

Nanobubbles have the potential to curtail the loss of oxygen during activated sludge aeration due to their extensive surface areas and lack of buoyance in solution. In this study, nanobubble aeration was explored as a novel approach to enhance aerobic activated sludge treatment and benchmarked against coarse bubble aeration at the lab scale. Nanobubble aerated activated sludge reactors achieved greater dissolved oxygen levels at faster rates. Higher soluble chemical oxygen demand removal by 10% was observed when compared to coarse bubble aeration with the same amount of air. The activated sludge produced compact sludge yielding easier waste sludge for subsequent sludge handling. The samples showed fewer filamentous bacteria with a lower relative abundance of floc forming Corynebacterium, Pseudomonas, and Zoogloea in the sludge. The microbiome of the nanobubble-treated activated sludge showed significant shifts in the abundance of community members at the genus level and significantly lower alpha and beta diversities.

Startup and initial operation of an MLE-MABR treating municipal wastewater.

A 630 m3/d pilot plant was installed at Subiaco WRRF to determine design and operational parameters of a hybrid Modified Ludzack-Ettinger - Membrane Aerated Biofilm Reactor (MLE-MABR) configuration. Two commercial ZeeLung MABR cassettes were installed in series in the anoxic zone and the pilot was fed with primary effluent (averaging COD 601 mg/L, TKN 68.5 mg/L and 17-29 °C). A nitrifying biofilm was developed within 3 weeks and the nitrous oxide (N2O) gas emissions from the MABR exhaust gas proved to be a reliable parameter to assess biofilm development. Both MABRs achieved the average nitrification rate (NR) of 3.7 gNH4-N/m2.d when air flow was 8.6 and 11.2 Nm3/h to MABR1 and MABR2 respectively, which reached a maximum oxygen transfer rate of 17.4 gO2/m2.d. Biofilm thickness was controlled via air scouring and intermittent coarse bubble mixing (90 s on/90 s off). This paper discusses the startup strategy, minimum requirements for process monitoring, impact of different air flow conditions, ORP and mixing patterns on performance efficiency over a 22-week period.

Size of biological flocs in activated sludge systems: Influence of hydrodynamic parameters at different scales

In conventional activated sludge (CAS) systems and membrane bioreactors (MBR), aeration, mixing and filtration are affected by various properties of activated sludge (AS) and especially viscosity and morphological properties of flocs. The aim of the present study was to understand the relationship between hydrodynamic conditions and AS floc size properties. Floc size distribution (FSD) measurements were performed in four systems showing different hydrodynamics: (i) a standard stirred reactor (SR), (ii) a pilot bubble column (BC), (iii) a full-scale aeration zone equipped with fine bubble diffusers, (iv) a full-scale filtration zone equipped with coarse bubble diffusers. The measurements were carried out on-site, using the mixed liquor from a full-scale MBR. The FSD of the given activated sludge mainly depends on the average shear rate (γ̇) and on the circulation time in the SR. To a lesser extent, local properties, such as maximal shear rate, also influence the FSD. In the same way, the main operating parameter governing the FSD in the BC was γ̇. For a similar γ̇, the flocs were slightly larger in the BC than in the SR. In addition, in the full-scale systems, for a similar γ̇ estimated, the FSD characteristic diameters were lower in the filtration zone (with coarse bubbles) than in the aeration zone (with fine bubbles). The FSD in the aeration zone was well correlated with the FSD in the BC whereas the flocs were slightly smaller in the filtration zone than in the BC.

Effects of coarse and fine bubble aeration on performances of membrane filtration and denitrification in moving bed membrane bioreactors

In this study, two lab-scale Moving Bed Membrane Bioreactors (MBMBR) were setup and operated in parallel to study the effect of coarse and fine bubble aeration on the performances of membrane filtration and denitrification treating domestic wastewater. The bacterial populations in the two MBMBRs were further analyzed to investigate the mechanisms involved in the different denitrification performances. The results showed that coarse bubble aeration could effectively mitigate membrane fouling by decreasing the formation of cake layer, although smaller sizes of bio-flocs were induced. In addition, coarse bubble aeration could also maintain dissolved oxygen (DO) at a relatively lower level without compromising the moving of bio-carriers, which achieved 10% higher total nitrogen removal rate due to anoxic zone created at inner layers of biofilms on bio-carriers. Accumulation of denitrifier (Thiobacillus denitrificans) on the bio-carriers was found under the coarse bubble aeration system, which can explain its superior denitrification performance.

Reverse Combined Microflotation of Fine Magnetite from a Mixture with Glass Beads

Magnetite is an essential iron-bearing mineral. The primary method of magnetite ore beneficiation involves successive steps of crushing, grinding, and magnetic separation. Reverse cationic flotation is used at the final stage to remove silicate and aluminosilicate impurities from the magnetite concentrate and reduce silica content to 1–3%, depending on metallurgical processing route (electrometallurgy, direct iron reduction). In view of the stringent demands of the magnetite concentrate grade, before flotation, the ore is currently routinely ground down to a particle size below 35 µm, and magnetite particles are ground to a size below 10 µm. This significantly reduces the efficiency of flotation and increases iron loss in the tailings due to the hydraulic report in froth being up to 15–25%. Combined microflotation (CMF) looks to be a promising method of increasing fine-particle flotation efficiency, as it uses relatively small amounts of microbubbles alongside conventional coarse bubbles. Microbubbles act as flotation carriers, collecting gangue particles on their surface, which then coarse bubbles float. The purpose of this study is to explore the effectiveness of CMF for processing a model mixture that contained magnetite particles smaller than 10 µm and glass beads (Ballotini) below 37 µm in size when the initial iron content in the mixture was 63.76%. Commercial reagent Lilaflot 821M was used as both collector and frother. The flotation procedure, which included the introduction of 15 g/t of the collector before the start of flotation, and the addition of 5 g/t of the collector in combination with a microbubble dose of 0.018 m3/t 6 min after starting flotation, ensured an increase in the concentrate grade to 67.63% Fe and iron recovery of 91.16%.

Combined microflotation of glass beads

It is well established that application of microbubbles in combination with coarser ones ensures a significant increase in the flotation efficiency of very fine (< 20 μm) and very coarse (> 100 μm) particles. The objective of this study is to determine the impact of microbubbles on the flotation efficiency of medium-sized particles (50−80 μm). In tests runs we used glass beads (ballotini) of various size grades in the range:50; 50−63; 63−71; 71−80 μm as flotation objects. We used CTAB as both a collector and a frother at the dosage of 0.06 mg per 1 g of ballotini. Prior to starting flotation by coarse bubbles, a dosage of microbubbles less than 60 μm in size in the form of a concentrated (66 vol. %) microbubbles dispersion in CTAB solution of (0.2 g L−1) produced by the MBGen-0.012 generator was fed into a flotation cell. The best flotation performance is observed for the fraction of 63−71 μm, whereas the flotation rate constants for all fractions are directly proportional to the volume dosage of microbubbles, when it does not exceed 0.2 mL g−1. The size of microbubbles significantly affects the flotation effectiveness and depends on the concentration of the collector/frother used for their production. The main mechanism of flotation performance enhancement through microbubbles application, involves formation of coarse aggregates comprising large number of microbubbles and particles, which provides for a significant increase in the capture efficiency of aggregates by coarse bubbles.