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Dissolved air flotation (DAF) is an effective method for separating suspended oil and solid particles from wastewater by utilizing small air bubbles. This study aims to investigate the impact of key factors, such as saturating pressure and water flow rate, on the separation of fine oil droplets from a water stream. The macroscopic flow patterns within the cell were analyzed using particle image velocimetry (PIV), while Digital Image Analysis (DIA) was employed to study microscopic phenomena, including oil droplet rising velocity and oil-bubble contact mechanisms. Our findings propose a safe operating window (specifically, water flow rate and saturation pressure) for the effective separation of oil droplets without any oil escaping into the clean water stream. It was found that the oil droplet rising velocity increases with the saturation pressure up to 200 kPa. However, a further increase in the pressure of the air saturating chamber leads to a decrease in oil droplet rising velocity. Additionally, we identified a peak in rising velocity at an oil droplet size of approximately 200 µm. Below this threshold, the rising velocity increases with droplet size, while for droplet sizes exceeding 200 µm, the rising velocity decreases with size. This behavior can be explained by the conflicting effects of droplet size increment according to the Stokes law for the rising velocity of oil droplets. As the droplet size increases, the average density of the bubbles/droplet aggregate rises, reducing the ∆ρ in the Stokes law and subsequently lowering the aggregate rising rate. However, as per the Stokes law, the oil droplet rising velocity increases proportionally to the square of its size. [ABSTRACT FROM AUTHOR]

Nowadays, moving bed biofilm reactors (MBBR) and dissolved air flotation (DAF) are frequently used in combination for the biological and physical treatments of synthetic oily wastes. The efficiency of the biocarriers utilized in MBBR is crucial since it has a big impact on the system's overall performance. A study was carried out utilizing a DAF-MBBR technique to treat synthetic oily wastewater in order to evaluate this. Two different kinds of biocarriers were used in this modified MBBR: polyethylene and plastic bottle caps. The result showed the DAF-MMBBRs process demonstrated excellent removal efficiencies for a range of parameters. Moreover, it seemed that DAF had higher COD, nitrite, nitrate, and turbidity removal efficiencies. For COD, the average removal efficiency was 39.62%; for oil and grease, it was 77.05%; and for ammonia, it was 39.71%. In the same way, MBBR1 is effective at eliminating phosphate, ammonia, TSS, and oil and grease. For COD, the average removal efficiency was 39.12%; for oil and grease, it was 94.10%; and for ammonia, it was 85.42%. The average removal efficiencies for COD, oil and grease, and ammonia in MMBBR2 were 38.76%, 84.95%, and 86.49%, respectively. Furthermore, Scanning electron microscopy (SEM) was used to assess the biofilm within the system. This revealed a well-developed biofilm layer on the interior surfaces of the biocarriers, improving the effectiveness of synthetic wastewater treatment. Excellent removal efficiencies were shown by the DAF-MBBR system for a range of parameters during a ten-day operational period. [ABSTRACT FROM AUTHOR]

Replacement of existing plastics derived from non-renewable and petrochemical sources will require the creation of new environmentally friendly polymers. Natural products such as protein containing waste generated from dairy factories have considerable potential for the development of bioplastics. Casein rich material (referred to as DAF-casein) harvested from dairy wastewater using a dissolved air flotation (DAF) procedure exhibits self-associating properties, and has potential for the formation of bioplastics, but produces brittle films. Inclusion of additional biopolymers such as polysaccharides and other proteins to form composites with the DAF-casein has the potential to improve the physical properties of such films. Three polymers, κ-carrageenan, sodium carboxymethylcellulose (NaCMC) and gelatin, were found to form homogenous solutions with DAF-casein. All three were successful in the formation of composite bioplastic films with improved morphology and water stability in combination with DAF-casein. The incorporation of additional polymers with dairy waste stream DAF-casein has the potential for the production of bioplastics. [ABSTRACT FROM AUTHOR]

This study concerns the application of computational fluid dynamics (CFD) and population balance equations (PBEs) in biphasic (water-air) simulations of the dissolved air flotation (DAF) process. The incorporation of population balance equations for simulation of the microbubble diameter distribution was based on the literature. The gas phase was simulated as being composed of two different phases: air 1 (d < 50 μm) and air 2 (d ≥ 50 μm). A non-homogeneous discrete model was applied and specific models enabled the prediction of phase change by breakage or coalescence. The models Turbulent and Luo were used to represent coalescence. The grid convergence index (GCI) method was applied for quantification of the discretization error of the tested computational grids. The grid selected for the simulations showed a discretization error of 5.17%. The results indicated that the velocity vectors of the aqueous phase presented stratified horizontal flow characteristics close to the surface and vertical plug flow inside the tank. The PBE results for the air volumetric fraction demonstrated that the coalescence model had a major impact in terms of the behavior of the gas phase in the white zone. Simulations indicated that the Luo model reduced in about 60% the air 1 concentration in the positions evaluated when compared with Turbulent model. [ABSTRACT FROM AUTHOR]

Highlights • A bacterial biosurfactant was applied as collector in a bench-scale DAF prototype. • The formulation and long-term stability of the biosurfactant was investigated. • Formulations were stored for 180 days and properties were determined. • The formulated biosurfactant showed stability at extreme conditions. • A CCRD was applied to the DAF prototype and the biosurfactant removed 92% of oil. Abstract The present study describes the formulation of a biosurfactant produced by Bacillus methylotrophicus UCP1616 and investigates its long-term stability for application as a collector in a bench-scale dissolved air flotation (DAF) prototype. For formulation, the conservative potassium sorbate was added to the biosurfactant with or without prior heat treatment at 80 °C for 30 min. After formulation, the biosurfactant samples were stored at room temperature for 180 days and the tensioactive properties of the biomolecule were determined with different pH values, temperatures and concentrations of salt. Then, a central composite rotatable design was used to evaluate the influence of the independent variables (effluent flow rate and formulated biosurfactant flow rate) on the oil removal efficiency in the DAF prototype. The formulated biosurfactant demonstrated good stability in both conservation methods, with tolerance to a wide pH range, salinity and high temperatures, enabling its use in environments with extreme conditions. The efficiency of the formulated biomolecule through heating and addition of sorbate was demonstrated by the 92% oil removal rate in the DAF prototype. The findings demonstrate that the biosurfactant from Bacillus methylotrophicus enhances the efficiency of the DAF process, making this technology cleaner. This biosurfactant can assist in the mitigation and management of industrial effluents, contributing toward a reduction in environmental pollution caused by petroleum-based hydrocarbons. [ABSTRACT FROM AUTHOR]

Due to requiring higher water quality standards over time, new technologies are being employed for wastewater treatment. Dissolved air flotation (DAF) and membrane bioreactor (MBR) technologies are widely employed as new technologies in wastewater treatment. DAF is used due to its excellent separation capability of suspended solids as well as oily material. MBR is used because it may provide a high level of mixed liquor suspended solids in a biological system and excellent separation capability too. In the investigation, separation by DAF, without addition of coagulant, could remove chemical oxygen demand by potassium dicromate (CODcr) up to over 70%, biochemical oxygen demand (BOD5) 73%, suspended solids (SS) 83%, total nitrogen (T-N) 55%, and total phosphorus (T-P) 65% in influent of municipal wastewater. Average overall removal rates of water quality parameters by the DAF-MBR system were very high such as CODcr 95.9%, BOD5 99.7%, chemical oxygen demand by potassium permanganate) 93.6%, T-N 69.8%, NH4-N 98.5%, T-P 78.2%, and SS 99.5%, which satisfy effluent water quality standards. Membrane separation in the MBR system produced a very low SS concentration of 1.27 mg/l in the final effluent. It was proven that DAF separation is an excellent technology for pretreatment of wastewater treatment, especially for an MBR system. [ABSTRACT FROM AUTHOR]

The Dissolved Air Flotation (DAF) system is a water treatment process that uses physical and chemical processes to remove suspended solids from water streams. The aim of this article is to put forward a new design for the DAF equipment system that includes an extra air diffuser in the separation zone, and to find optimal operating conditions to make water more acceptable for an end-use. Computational fluid dynamics (CFD) were used to assess three operating conditions with the new equipment design, which led us to conclude that case III offers better separation results due to the presence of stratified flow. [ABSTRACT FROM AUTHOR]

Highlights: [•] Dissolved air flotation (DAF) was studied for treatment of 2m-% O/W emulsions. [•] Either PosiDAF or conventional coagulation–flocculation and DAF was performed. [•] Chemicals used in the DAF studies were CTAB, Epi–DMA and PolyDADMAC. [•] PosiDAF performed very well, especially with PolyDADMAC. [•] Flow cytometry proved to be a promising analysis method for waters containing oils. [ABSTRACT FROM AUTHOR]

Restaurant dishwashers consume a large quantity of fresh water and produce significant amounts of high strength oily wastewater which may cause serious problems when discharged into the sewer. An analysis of restaurant dishwasher effluent (RDE) from a busy upscale restaurant identified high levels of oil and grease, chemical oxygen demand (COD), biochemical oxygen demand (BOD), alkalinity, pH, and chlorine, but low levels of nitrogen and phosphorus. In this study, RDE was treated using an internationally patented chemical dissolved air flotation (chemical DAF) system. The chemical DAF system was designed so that coagulation, flocculation, and flotation processes could be carried out within the same reactor. The treatment system is therefore small and compact and suitable for use in restaurants where space is limited. The treatment performance of the chemical DAF was evaluated by determining optimal process conditions, contaminant removal efficiencies, and residual contaminant concentrations. It was found that removal efficiencies of 98.90%, 93.16%, 98.68%, 90.04%, and 88.20% could be achieved under optimal process conditions for turbidity, oil, TSS, BOD5, and COD, respectively. Total coliform and E. coli were not detected in either the raw dishwasher effluent or the treated dishwasher effluent due to the use of sodium hypochlorite as a dishwashing sanitizer. Water quality of the treated effluent met the criteria put forth in the Canadian Guidelines for Domestic Reclaimed Water for Use in Toilet and Urinal Flushing, with the exception of BOD5. Present findings suggest that chemical DAF is a promising treatment process for the removal of contaminants from restaurant dishwasher effluent. [ABSTRACT FROM AUTHOR]

Preliminary testing of dissolved air flotation (DAF) for wastewater treatment is presented. A combined coagulation-flocculation/DAF column system is used to remove oil and Co from nuclear industry wastewater. In this work, operational conditions and coagulant/flocculant concentrations are optimized by varying pH. Determinations of air-solids ratio ( G/ S), retention time ( θ) , pressure ( P), volume of depressurized air-water mixture ( V), turbidity and Co concentrations are reported. The effect of the treatment on the efficiency of separation of oily residues is also discussed. The results establish that the coagulant/flocculant system, formed by a modified polyamine (25 mgL) and a slightly cationic polyacrylamide (1.5 mgL), under specific operational conditions (pH = 7, mixing intensity Im = 300 s and Im = 30 s), allowed the destabilization of colloidal matter, resulting in resistant flocs. It was concluded that by using G/ S = 0.3, θ = 15 min, P = 620 kPa and V = 0.0012 m, the greatest percentage removals of oil, turbidity, total cobalt and Co were obtained. These preliminary results then show that dissolved air flotation represents a good alternative for treatment of nuclear industry wastewater contaminated with radionuclides. [ABSTRACT FROM AUTHOR]

Abstract: A novel approach was developed to enhance the efficiency of the dissolved air flotation (DAF) for biodiesel wastewater by acidification and coagulation. Firstly, Grease & Oil and Chemical oxygen demand (COD) removal efficiencies of biodiesel wastewater using acidification with pure hydrochloric acid and pure sulfuric acid at pH=3 and 1day retention time were more than 80%, and 50%, respectively. Secondly, Grease & Oil and COD removal efficiencies of biodiesel wastewater using alum, polyaluminum chloride and ferric chloride coagulants without acidification at 1.0g/L were more than 90% and 30%. Thirdly, DAF alone and DAF with acidification could not separate Grease & Oil from biodiesel wastewater. Thus, DAF with the acidification and coagulation is suggested for biodiesel wastewater treatment. Biodiesel wastewater treatment by acidification before alum coagulation allowed the alum concentration to be reduced by 60–90% compared to treating without acidification. In addition, the efficiency of Grease & Oil removal from biodiesel wastewater by DAF with alum and acidification was 85–95%. It can be concluded that the efficiency of Grease & Oil removal from biodiesel wastewater using DAF with acidification and coagulation was 10% greater compared to other processes. [Copyright &y& Elsevier]

Abstract: For pretreatment of wastewater discharged from personnel care products (PCPs) factory, two treatment schemes were investigated. The 1st step in both schemes was chemical coagulation followed by precipitation in the 1st scheme and dissolved air flotation in the 2nd one. Ferric chloride (FeCl3·6H2O), alum (Al2(SO4)3·18H2O) and ferrous sulfate (FeSO4·6H2O) were used as coagulants. Lime (CaO) was used as coagulant aid and for pH adjustment. For C/P, the three coagulants investigated were found to be more or less similar in their performance. Maximum CODtotal removal obtained by ferric chloride, ferrous sulfate and alum was 75.8±9.7, 77.5±9.6 and 76.7±9.9%, respectively. Corresponding BOD5 total removal values were 78±15.8, 78.7±15.6 and 74.1±19.3%, respectively. However, the optimum dose of ferric chloride and alum was 600 and 700mg/l while that of ferrous sulfate was 850mg/l. Alum produced a voluminous sludge, but with the least solids content. Ferric chloride produced compact sludge with a good settleability as reflected by the low sludge volume index (SVI) of 76.3±28.8ml/gTSS. In the coagulation–dissolved air flotation (C/DAF) experiments, the results showed that alum produced higher COD removal (77.5±3.2%) as compared to ferric chloride (71.6±2.9%) and ferrous sulfate (67.7±3.7%). A cost evaluation of the initial investment and the running costs using the different coagulants at their optimum operating conditions were calculated. The investment and running cost for C/P process is higher by 27.3 and 23.7% than C/DAF. [Copyright &y& Elsevier]

This paper aims to investigate the influence of some dissolved air flotation (DAF) process variables (specifically: the hydraulic detention time in the contact zone and the supplied dissolved air concentration) and the pH values, as pretreatment chemical variables, on the micro-bubble size distribution (BSD) in a DAF contact zone. This work was carried out in a pilot plant where bubbles were measured by an appropriate non-intrusive image acquisition system. The results show that the obtained diameter ranges were in agreement with values reported in the literature (10-100 μm), quite independently of the investigated conditions. The linear average diameter varied from 20 to 30 μm, or equivalently, the Sauter (d3,2) diameter varied from 40 to 50 μm. In all investigated conditions, D50 was between 75% and 95%. The BSD might present different profile (with a bimodal curve trend), however, when analyzing the volumetric frequency distribution (in some cases with the appearance of peaks in diameters ranging from 90-100 μm). Regarding volumetric frequency analysis, all the investigated parameters can modify the BSD in DAF contact zone after the release point, thus potentially causing changes in DAF kinetics. This finding prompts further research in order to verify the effect of these BSD changes on solid particle removal efficiency by DAF. [ABSTRACT FROM AUTHOR]

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 also addressed. The review showed that the hybrid flotation membrane system can achieve high separation performance with reasonable price compared with the traditional DAF or membrane-based filtration systems. This extends the use of this emerging technology to treat new types of wastewater or improving the existing technologies which reduce the effect of harmful effluents on the surrounding environment. Moreover, using flotation in combination with MF/UF has reduced membrane fouling and extended their useful working time. This leads to a reduction in operation cost and improves the efficiency of membrane performance. Hybrid flotation-NF/RO is a new technology for wastewater treatment which produces high quality water with greater recovery and lower energy and reagents consumption. Finally, the review also addressed the new application of DAF as pretreatment for the desalination processes. [ABSTRACT FROM AUTHOR]

The feasibility of a hybrid system consisting of powdered activated carbon (PAC) adsorption and dissolved air flotation (DAF) processes was examined for the simultaneous removal of algae (anabaena and mycrocystis) and their secondary algal metabolites (2-methylisoboneol and geosmin). Before studying the hybrid system, adsorption equilibrium and kinetics of organics (2-methylisoboneol and geosmin) produced from algae on three powdered activated carbons (wood-based, coal-based, coconut-based) were studied. The flotation efficiency of algae and PAC in DAF process was evaluated with zeta potential measurements. Interestingly, we found that the agglomerate of bubble and PAC particle can be successfully floated by DAF. In addition, the simultaneous removal of algae and organics (i.e., secondary algal metabolites) dissolved in water can be achieved by using the hybrid system of adsorption/DAF processes. [ABSTRACT FROM AUTHOR]

In this report the performance of the Bayer Flotation Technology BayFlotech(r) is demonstrated by comparing process data with figures published by the German Deutsche Vereinigung fur Wasserwirtschaft, Abwasser und Abfall e.V. (ATV) and Verband Deutscher Maschinen u. Anlagenbau e.V. (VDMA) associations. In addition experience gained under plant operation is described. Inter alia the relation between the air/solid dosage rate and the specific solids loading is discovered. It was found that the specific air dosage can be decreased with increasing solids loading rates: whereas the specific air dosage is up to 35 l/kg TSS at solids loading 95%) for every compared situation. Finally we report on the newly developed 'phasemixer', which allows high water saturation rates (>95%) and preventing lather. [ABSTRACT FROM AUTHOR]

The flow patterns of the contaminated water and the air bubbles inside a large-scale Dissolved Air Flotation (DAF) tank were examined using CFD modelling. The DAF tank was operating off-nominally in the sense that it was supplied with bubbles larger than originally designed for. Attention was drawn to the location for air injection and the effect of having more than one-size bubbles in the tank, regarding the good contact between phases and the subsequent bubble recovery at the tank free surface. The role of the inclination of the internal baffle of the tank and liquid flow rate was also examined. [ABSTRACT FROM AUTHOR]

The capture of particles by air microbubbles in dissolved air flotation has been analysed using a one-step (holistic) approach, which numerically solved the motion equation (with the inclusion of microhydrodynamic resistance functions and surface forces) for both the bubble-particle collision and attachment interactions. Model predictions with the inclusion of non-DLVO attractive surface force agreed with the experimental trajectories of latex particles. The non-DLVO attractive force reduced the force barrier between non-attaching particles and bubbles, and significantly increased the attractive net force between attaching particles and air bubbles. [ABSTRACT FROM AUTHOR]

Particles from a post denitrifying Kaldnes Moving Bed™ Process were studied using an optical borescope, a visualisation technique that provides opportunities for both qualitative and quantitative studies of the separation mechanism in Dissolved Air Flotation (DAF). Rise rates for particle/bubble aggregates were estimated showing great variability. Two groups of aggregates were distinguished; relatively small flocs (<100 µm) with single bubbles attached rising comparatively slowly and large flocs (>100 µm) with several bubbles attached rising very fast. The high rise rates for large aggregates are discussed, possibly explained and suggested as the reason for the effective separation of large particles noticed in previous studies. Removal efficiency of different size categories of particles in DAF were investigated on the basis of particle size analysis indicating increased separation efficiency with increasing particle size. [ABSTRACT FROM AUTHOR]

Secondary stickies refer to sticky material in recycled fiber process streams, which has been dissolved in one part of process, but turned to solid phase due to changes in process conditions. The material that can later form secondary stickies is called potential secondary stickies. A new, fast, and simple method for measuring the amount of potential secondary stickies was developed to measure the purification result in the deinked pulp (DIP) filtrates. The new method, now called potential secondary stickies method, was tested with process waters from a recycled fiber (RCF) plant. The method was found to be reliable. Several chemicals and chemical combinations were tested in laboratory scale and compared as coagulation- flocculation agents in two dissolved air flotations (DAF) used as internal water treatment units at the RCF plant. With potential secondary stickies method, significant differences between the effectiveness of the chemicals were found, whereas no difference was seen in the quality of purified process water with traditional measuring methods. The measurement method was also used in mill during a two-week measuring period. As a conclusion, it can be said that this method can be used to monitor the quality and to predict the changes in DIP process water. [ABSTRACT FROM AUTHOR]

Successful mineral processing depends largely on the adequate consideration of its interactions with water. Considering water scarcity and the cost for the use of a fresh water, the mineral industry has been looking for viable alternatives for the reuse of process water. However, recycling water from tailings dams can contain large amounts of dissolved species, particulate matter, organic matter from residual reagents, etc., which negatively affect the ore concentration stage. In this work, the deleterious effects of calcium, magnesium, and phosphorus ions, present in recycling water, on the apatite flotation performance have been quantified. It also investigated the use of dissolved air flotation (DAF), associated with coagulation/flocculation treatment to remove most of the contaminants present in the water. Effect of pH on this combined process of wastewater treatment has also been investigated. Removal efficiencies of calcium, magnesium, and phosphate ions and also turbidity have been measured. Water from a tailing dam of an apatite processing industry has been treated by this technique and the produced water used in the flotation of apatite in column. Results have shown that the use of recycling water after the wastewater treatment proposed in this work led to a good performance of apatite flotation, leading to recovery (80.5%) and grade (31.2%) of P 2 O 5 highest than minimum acceptable in this industry. • DAF with pretreatment exhibited good performance for reuse of process water. • Coagulation and flocculation improved the DAF process performance. • Calcium magnesium and phosphorus ions had deleterious effects on apatite flotation. • The best operating conditions for high removal efficiency of ions was identified. • Experiments of apatite flotation using the treated water presented good performance. [ABSTRACT FROM AUTHOR]