Dissolved Air Flotation Process Research Articles

Evaluation of Model Simulation and Field Experiment on Collision-Attachment Efficiency for Operational Factors in Dissolved Air Flotation Process

This study conducted a series of tests and simulations to estimate collision-attachment efficiency using a trajectory analysis method, to evaluate model sensitivity due to major impact factors in designing and operating dissolved air flotation (DAF) for the various types of wastewaters, and to find the possibility of model application in determining the flotation efficiency of DAF. Collision-attachment efficiency between a bubble and a particle in the model is described by hydrodynamics related to stream function in Stokes’ flow and surface forces based on a classic DLVO theory, encoded using Matlab language software, and performed numerical analysis using the 5th Runge-Kutta method. Model simulation examined the effects of two major factors, size and zeta potential, on collision-attachment efficiency during flotation and field experiment evaluated to model results. Both results from the simulation and field experiment indicated that the larger particles presented the better collision and removal efficiency and the effect of particle zeta potential on collision-attachment efficiencies was increased as the particle zeta potential increased from the negative domain to the positive domain. Therefore, the collision-attachment efficiency model using the trajectory analysis method may be used in estimating the flotation efficiency and in explaining its characteristics.

Monitoring and treatment of selected nanoparticles

With their increasing use, nanoparticles will become concentrated in urban effluents in the future. Both adequate monitoring methods and water treatment technologies will be necessary to assess and avoid consumer exposure. This paper reports results in these two challenging areas for both organic and inorganic nanoparticles. Treatment experiments indicate that lamellar settling is better adapted than dissolved air flotation for SiO(2) nanoparticles removal. The use of 120 mg/L of Aqualenc coagulant without flocculant addition allows 99% removal to be achieved for an initial concentration of 1 g/L. On the other hand, the dissolved air flotation process implemented under the usual industrial conditions does not permit removal of SiO(2) nanoparticles. In this case SiO(2) removal occurs only by settling in the flocculator tank. Application of a high resolution liquid chromatography/mass spectrometry (LC/MS) technique to a small selection of treated urban effluents indicates that C(60) fullerenes are not yet widely distributed in effluents; however non-point sources cannot be entirely ruled out.

Elimination of TiO2 nanoparticles with the assist of humic acid: Influence of agglomeration in the dissolved air flotation process

With recent advances in nanotechnology, environmental and health consequences of nanomaterial disposal merit close attention. In the search for environmentally-friendly reagent, this study investigates the use of humic acid (HA) as an assist of dissolved air flotation (DAF) in the TiO2 nanoparticle (TNP) elimination. To determine mechanisms of TNPs interacting with HA, surface modification experiments were firstly carried out; thereafter, laboratory scaled DAF tests were applied to remove TNPs with HA assisting. Results of surface modification experiments showed that the zeta potential of TNP suspension system had a reversal trend due to counter ions of TNP and anions offered by the HA stock solution. The surface modified suspension was not easy to restabilize because of the close combination of TNPs and HA through sphere linkages or hydrogen-bonded surface complexes. Agglomeration took place more readily along with increasing HA concentration in the optimum dosage range (7.8-9.15mg/L DOC). The flotation performance revealed that HA could improve the DAF efficiency in the optimum dosage range of HA. The interaction between TNPs and HA (Na+-humate), including surface charge neutralization (electrostatic interactions), sphere linkages or hydrogen-bonded surface complexes, hydrophobic interactions, and van der Waals interactions, played dominant roles.

Microbubble histogram reconstruction by nonlinear frequency mixing

In the 4th generation sodium fast nuclear reactors (SFR), different phenomena can lead to gaseous microbubbles presence in the primary liquid sodium pool. This paper investigates the ability of nonlinear acoustics techniques to characterize these microbubbles presence. The goal is here to determine the void fraction (volume fraction of free gas) and the histogram of bubbles radius. Different acoustic techniques are currently developed at CEA. Among others, the nonlinear mixing of two frequencies [V. L. Newhouse and P. M. Shankar, J. Acoust. Soc. Am. 75(5), 1473–1477 (1984)] is under study. Based on the nonlinear behavior of bubble resonance, this technique allows determining the radius histogram of a bubble cloud. Two different mixing techniques are here presented: the mixing of two high frequencies and the mixing of a high and a low frequency. The first step is an air-water experimental set-up. Microbubbles clouds are generated with a like dissolved air flotation process and an optical device gives us reference measures. Generated bubbles have radii in the range of several microns to several tens of microns. The developed experimental procedure allows us to determine the bubble size’s histograms with accuracy never reported yet.

Association of dissolved air flotation (DAF) with microfiltration for cyanobacterial removal in water supply

ABSTRACT The removal of filamentous cyanobacteria in natural water was investigated by a sequential treatment involving dissolved air flotation (DAF) (preceded by coagulation/flocculation) and microfiltration (MF) technologies. The combined treatment was considered to evaluate the contribution of the DAF process as a pre-treatment for MF to mitigate the impact on the microfiltration performance caused by the presence of the cells. The bench-scale experiments were conducted with surface water samples. For C/F steps, a dose of 40 mg L−1 of aluminium sulphate was used, and several operational conditions were adopted for the DAF tests. For the MF experiments, polyvinylidene fluoride (PVDF) membranes (0.3 μm) and a working pressure of 1 bar were used. The parameters colour, turbidity, UV254 nm absorbance, DOC and cyanobacterial density, were evaluated. The DAF-MF sequence showed a considerable reduction in the residual values for all parameters compared with the DAF process alone. MF was able to remove cyanobacterial cells completely. The use of DAF as an MF pre-treatment indicated an increase in the percentages of removal. However, the particulates remaining in the water from the DAF process resulted in clogging of the membrane. The results indicate that the association of DAF and MF technologies can be a viable option to be used for water treatment with cyanobacterial cells.

양식장 배출수 수질관리를 위한 용존공기부상 공법의 운전 인자 영향 분석

Pollutants in aquaculture system effluent mostly originated from solid wastes including uneaten feed and excreta of cultured species. In this research, DAF(Dissolved Air Flotation) unit is suggested as an integrated solid control unit especially as a form of IIBG(Inline Injection Bubble Generation) process in aquaculture system. Solid removal performance of DAF unit was examined under various operation and salinity conditions with turbidity and suspended solid. Solid waste removal efficiencies were found to be affected by operation conditions including saturator pressure, recycle ratio, coagulant concentration. Solid removal efficiency was higher under higher saturator pressure and recycle ratio under which condition larger number of bubbles is generated. Coagulant is thought to have important role in creating bubble-particle aggregate by showing better removal efficiency with higher concentration. However higher saline water showed less effectiveness in removing solids by DAF(IIBG). Application of DAF(IIBG) process also showed additional effect in phosphate removal and DO(Dissolved Oxygen) supply. Phosphate existed in polluted water was removed up to 46% after treatment, which is thought to attribute to aluminium phosphate precipitation. And DO concentration was found to increase over 50% of initial saturation concentration after the injection of micro-bubbles. Through experiments on solid removal from aquaculture effluent, DAF(IIBG) process is estimated to be effective solid control method. This property can help aquaculture system being installed and operated simply and effectively.

Removal of emulsified fuel oils from brackish and pond water by dissolved air flotation with and without polyelectrolyte use: Pilot-scale investigation for estuarine and near shore applications

In coastal areas, estuaries, and inland waters, dispersant use after oil spills is not allowed due to sensitivity of the ecosystems. The purpose of this study was to investigate the removal of emulsified fuel oils from brackish and pond water by dissolved air flotation (DAF) with and without use of coagulants. Experiments were conducted with a 60 L DAF system. Fuel oil–water emulsions were prepared with regular unleaded gasoline, jet fuel, and diesel fuel mixed at 1:1:1 (v/v/v) ratio. Batch and continuous runs were conducted at air pressurization of 354.6 kPa. During both batch and continuous modes, significant petroleum hydrocarbon (PHC) removal was achieved within 10 min. Coagulant addition initially increased the PHC removal by about 5–15%. However, effectiveness of the coagulant was not significant after 20 min due to breakage of the aggregates. In general, the pond water had higher PHC removal than the brackish water. With longer run times, PHC removal improved slightly and the effluent contained increasing fractions of higher molecular weight compounds indicating that PHC removal was due to both DAF and stripping processes. Results indicate that DAF process can be effective both with and without the use of coagulants for removing PHCs from brackish and pond waters.

Replacing Synthetic with Microbial Surfactants as Collectors in the Treatment of Aqueous Effluent Produced by Acid Mine Drainage, Using the Dissolved Air Flotation Technique

Dissolved air flotation (DAF) is a well-established separation process employing micro bubbles as a carrier phase. The application of this technique in the treatment of acid mine drainage, using three yeast biosurfactants as alternative collectors, is hereby analyzed. Batch studies were carried out in a 50-cm high acrylic column with an external diameter of 2.5cm. High percentages (above 94%) of heavy metals Fe(III) and Mn(II) were removed by the biosurfactants isolated from Candida lipolytica and Candida sphaerica and the values were found to be similar to those obtained with the use of the synthetic sodium oleate surfactant. The DAF operation with both surfactant and biosurfactants, achieved acceptable turbidity values, in accordance with Brazilian standard limits. The best ones were obtained by the biosurfactant from C. lipolytica, which reached 4.8 NTU. The results obtained with a laboratory synthetic effluent were also satisfactory. The biosurfactants removed almost the same percentages of iron, while the removal percentages of manganese were slightly higher compared with those obtained in the acid mine drainage effluent. They showed that the use of low-cost biosurfactants as collectors in the DAF process is a promising technology for the mining industries.

Polymers as bubble surface modifiers in the flotation of algae

Previous research has shown that dosing polymers directly to the saturator of a dissolved air flotation (DAF) process in replacement of upstream coagulation can achieve algae removal comparable to that of conventional treatment, as a result of bubble modification. In this paper we further explore the application of polyDADMAC as a bubble modifier in this adapted DAF process. It was determined that removal improved with increasing polyDADMAC molecular weight (MW). Removal efficiencies obtained for Microcystis aeruginosa were much greater than those predicted theoretically, and were attributed to a potential projection of the polymer into the aqueous phase, increasing the swept volume of the bubble. PolyDADMAC dose and the resultant removal efficiency were dependent on the character of the associated algogenic organic matter (AOM). The AOM with high MW, low charge and significant hydrophobicity and protein content enabled co‐operative binding, while that of high charge and low hydrophobicity hindered attachment.

Performance of Presedimentation and Dissolved Air Flotation to Overcome Highly Turbid Raw Water

Simultaneous removal of inorganic and algae particles is frequently required during the rainy season in Korea. Although the dissolved air flotation (DAF) process has been successfully applied to the treatment of algae-laden water with low turbidity, it is known that inorganic particles caused by rainfall can highly affect flotation efficiency. A small presedimentation basin was constructed to overcome the decrease in treatment efficiency for the DAF process when highly turbid raw water flows in because of heavy rain in the Songjeon water treatment plant. In this study, a series of operational data from the past 3 years and 9 months was investigated and analyzed to explore the effectiveness of presedimentation and derive empirical information on a complementary operation technique for the combining the presedimentation and DAF processes. For the treatment of highly turbid raw water during the rainy season, solids loadings, including larger particles, decreased substantially with the application of presedimentation in the Songjeon water treatment plant during the rainy season. However, the evaluation results of the particle size distribution indicated that the smaller particles need to be removed by a filtration process even though the DAF process is effective for decreasing solids loadings.

Evaluation on simultaneous removal of particles and off-flavors using population balance for application of powdered activated carbon in dissolved air flotation process

Most of the water treatment plants applying the DAF process are faced with off-flavors control problems. For simultaneous control of particles of impurities and dissolved organics that cause pungent taste and odor in water, an effective method would be the simple application of powdered activated carbon (PAC) in the DAF process. A series of experiments were carried out to explore the feasibility for simultaneous removal of kaolin particles and organic compounds that produce off-flavors (2-MIB and geosmin). In addition, the flotation efficiency of kaolin and PAC particles adsorbing organics in the DAF process was evaluated by employing the population balance theory. The removal efficiency of 2-MIB and geosmin under the treatment condition with kaolin particles for simultaneous treatment was lower than that of the individual treatment. The decrease in the removal efficiency was probably caused by 2-MIB and geosmin remaining in the PAC particle in the treated water of DAF after bubble flotation. Simulation results obtained by the population balance model indicate, that the initial collision-attachment efficiency of PAC particles was lower than that of kaolin particles.

Effects of ozone in treating drinking water by DAF system

The Dissolved Air Flotation (DAF) process is very effective in removing low density floc particles for drinking water treatment. It is especially well known in removing turbidity and algae by flotation process. The micro-bubbles in the DAF process pick up small flocs, thereby turbidity materials and floated algae are removed efficiently. When air is substituted by ozone in the DAF process, the removal rates of water quality parameters are highly enhanced including turbidity and algae. The turbidity removal rate is enhanced by 1.1% while the removal rate of THMFP is increased by 11.7%. Other parameters such as TOC, and microbial agents are also removed greatly by using ozone instead of air in DAF system.

A hybrid flotation–membrane process for wastewater treatment: an overview

Wastewater produced from many industries such as dyeing, textile industry, minerals processing/ phosphate beneficiation, food processing and deinking is either reused after being treated by conventional treatment methods or pumped to drainage systems without treatment. This represents a serious environmental problem and causes challenges to the countries which face water shortages. A hybrid dissolved air flotation (DAF)-membrane process is a promised technology which can be used for treatment of many types of wastewater. Froth flotation is usually used to remove large proportion of suspended or dissolved solids while the membrane cell can reject very small particles. In this paper, a comprehensive review on the treatment of wastewater using DAF process alone as well as a hybrid flotation membrane was discussed. Various ways of hybrid flotation–membrane filtration such as flotation–microfiltration (MF), flotation–ultrafiltration (UF), flotation–nanofiltration (NF), and flotation–reverse osmosis (RO) are al...

Characteristics of Pretreatment Parameters and Bubble Size Influencing DAF Efficiency

This study attempted to investigate the relationship between the floc size and efficiency of a DAF (Dissolved Air Flotation) method using a PDA (Photometric Dispersion Analyzer), which is used to monitor floc generation via on-line access. This study applied actual measurements to investigate how the size of bubbles affected the flotation velocity, and introduced similar results to the theoretical flotation velocity reported in the literature. The results were found to play a role in improving the reliability in the evaluation of the flotation velocity of floc-bubble aggregates. From the results of the evaluation of the electrostatic characteristics for application to DAF treatments, the amount of coagulants was determined on the basis of the zeta potential value, which had to be controlled in the order of +2 ∼ + 5 mV to improve the treatment efficiency. The results of the rapid mixing intensity test using a PDA demonstrated that G value of 900 sec−1 for 1 ∼ 3 sec provided excellent treatment efficiencies in a DAF process. In addition, from the results of the flocculation test based on the flocculation index, the flocculation combination of 70/50 sec−1 gave reasonable results for DAF operation.

The Potential for Using Bubble Modification Chemicals in Dissolved Air Flotation for Algae Removal

This paper investigates the potential for using surface modified bubbles in the treatment of algae using dissolved air flotation (DAF) instead of upstream coagulation and flocculation. Bubble modification is attempted by adding either metal coagulant, surfactant or polymers direct to the saturator. In this way, the chemical characteristics most suitable for removing small algae cells using this technique are examined. Optimum removal using metal coagulant, aluminium sulphate, was 60%; however, both a decrease in the magnitude of the zeta potential and microfloc generation occurred concurrently, thus accounting for the improved removal. In contrast, there was no change in system zeta potential and no microfloc generation when using cationic surfactant cetyltrimethyl-ammonium bromide (CTAB), for which 63% removal was achieved. An average of 95% removal was achieved using the cationic polymer, PolyDADMAC, with no change to system zeta potential. The results therefore confirm that there is a potential for adapting the conventional DAF process to operate without upstream coagulation and flocculation. A chemical with both a hydrophobic component in addition to a high molecular weight, hydrophilic, highly charge component is advised for the process.

A study on the efficiency of the DAF (dissolved air flotation) process using ozone injection

In this study, dissolved ozone flotation system with injecting ozone directly into a DAF pump developed was applied to remove turbidity and organic matter for water treatment. This ozone flotation system was evaluated on the basis of the efficiency of ozone transfer into water and the removal efficiency of turbidity and TOC in the Nakdong river water. The DAF pump system found to be more efficient than the conventional DAF system injecting ozone directly from a ozone generator. The ozone through the DAF pump process was dissolved in water much faster than through the general ozone generator due to the higher mixing efficiency through a pump impeller and high pressure inside the DAF pump. Also, the kinetics of ozone decay injected by the DAF pump was slower than injected by an ozone generator. The DAF pump flotation system shows that 30% difference of removal efficiencies is attained as the ozone dose increases from 1.2 mg/L to 8.2 mg/L. And the turbidity removal was increased with increasing ozone dose. Therefore it can be concluded that ozone in this flotation system facilitates improved removal of organic matter and turbidity due to enhanced destabilization of those.

Low energy ballasted flotation

A novel process which involves the replacement or supplementation of bubbles in the dissolved air flotation process with low density beads is presented. The work comprised a series of bench-scale flotation trials treating three commonly encountered algal species ( Microcystis, Melosira and Chlorella) that were removed in a flotation cell configured as either: conventional dissolved air flotation (DAF); ballasted flotation using low density 70 μm glass beads with a density of 100 kg m −3; or a hybrid process of ballasted flotation combined with conventional DAF. Results indicated that the bead only system was capable of achieving better residual turbidity than standard DAF at bead concentrations of 500 mg L −1. Addition of beads in combination with standard DAF reduced turbidity further to even lower residual turbidity levels. Algae removal was improved when glass beads were dosed, but removal was dependent on algal species. Microcystis was removed by 97% for bead only systems and this removal did not change significantly with the addition of air bubbles. Melosira was the next best removed algae with bead only dosed systems giving similar removals to that achieved by standard DAF using a 10% air recycle ratio (81 and 76% removal respectively). Chlorella was the least well removed algae by bead only systems (63% removal). However, removal was rapidly improved to 86% by the addition of air bubbles using only a 2% recycle ratio. Energy estimations suggested that at least a 50% energy reduction could be achieved using the process offering a potential route for future development of low energy separation processes for algae removal.

Treatment of meat industry wastewater using dissolved air flotation and advanced oxidation processes monitored by GC–MS and LC–MS

The meat processing industry generates a large amount of wastewater which represents a serious problem due to their high levels of organic matter which demands effective and high cost treatments. In the present study the effectiveness of the wastewater treatment by dissolved air flotation (DAF) followed by advanced oxidation processes (AOPs) using photo-peroxidation (H 2O 2/UV) and photo-Fenton reactions were evaluated in laboratory scale. The primary treatment was carried out in a DAF system, using optimal dosages of ferric sulfate and coagulation aids. The efficiency of these processes was evaluated through the following parameters: COD, BOD 5, color, turbidity, total solids, fixed solids and volatile solids, both before and after the DAF and AOP treatments. The elimination efficiency of pollutants was monitored by gas chromatography–mass spectrometry (GC–MS) and liquid chromatography–mass spectrometry (LC–MS) analysis. The results had shown that the DAF treatment efficiently reduced the COD, color, turbidity and total solids contents. In addition, the advanced oxidation process increased the organic matter removal of the treated samples. Among the AOPs, the photo-Fenton reaction reached the best overall results. These results show that the DAF process followed by an AOP process might be efficient for meat wastewater treatment, intended or not to water reuse purposes.

Rise velocity verification of bubble-floc agglomerates using population balance in the DAF process

The dimension of the separation zone in the dissolved air flotation (DAF) process is practically determined by the rise velocity of the bubble-floc agglomerates: flocs attached to several bubbles. To improve the flotation velocity and particle removal efficiency in the DAF process, many researchers have tried to attach as many bubbles as possible to flocs. In this study, the rise velocity of bubble-floc agglomerates, considered to be the most important factor in designing the separation zone of the flotation tank in the DAF process, was investigated on the basis of comparison between theoretical and observed results. The observed rise velocity measured by a particle image analyser (PIA) and the predicted value, however, did not show similarity, in contrast to what we had expected. Furthermore, the simulated results using population balance to predict the maximum number of attached bubbles on a floc were too impractical to accept under the practical condition of the surface of the floc if there was no change of bubble size. These findings led us to suggest that there were three possible causes which could conceivably explain the observations. It was suggested that the differences between predicted and observed values could be attributed to one or more of the possible causes.

Measurement of bubble bed depth in dissolved air flotation using a particle counter

In the development of dissolved air flotation (DAF) technology, it is noteworthy that higher hydraulic loading rates are achieved while the reactors become deeper resulting in a smaller footprint. One of the reasons for the increased efficiency is claimed to be the deeper bubble bed depth in the flotation separation zone; however, there has been limited research on the characterization of the bubble bed. In this research, a method for locating the bubble bed interface using a commercially available particle counter is presented. The results compared remarkably well with observations by the naked eye at a pilot plant with a transparent acrylic wall. The method is then applied to locate the bubble bed interface at an operating DAF plant in Wonju, Korea. We can observe that the bubble bed profile changes according to the operational conditions and that higher effluent water quality is obtained with a deeper bubble bed. Based on these results, optimization of DAF process might be possible by monitoring the bubble bed profile in the reactor.