Dissolved Air Flotation Research Articles

Electrochemical treatment enhancment with dissolved air floatation to minimise organic pollutants of leachate in the press stations in Baghdad

Leachate is a complex solution of contaminants produced from municipal waste compacting stations, being primarily comprised of household waste. In this research, leachate was treated in an electrochemical batch process with a dissolved air floatation system using aluminium as the anode with cathode electrodes. Conditions such as pH, current density (i), contact time, and air flowrate were varied and tested to determine their effects on the removal efficiency in terms of Chemical Oxygen Demand (COD), Oil, and Turbidity (Turb.). Under the best conditions, the removal efficiencies for oil, COD, and turbidity were 78.7%, 77.5%, and 98.6%, respectively, suggesting that this method can be considered an efficient and effctive treatment for leachate.

Measuring Biofouling Potential in SWRO Plants with a Flow-Cytometry-Based Bacterial Growth Potential Method.

Measuring the bacterial growth potential of seawater reverse osmosis (SWRO) feed water is an issue that is receiving growing attention. This study developed and demonstrated the applicability of the flow-cytometry (FCM)-based bacterial growth potential (BGP) method to assess the biofouling potential in SWRO systems using natural microbial consortium. This method is relatively fast (2–3 days) compared to conventional bioassays. The effect of the potential introduction of nutrients during measurement has been studied thoroughly to achieve the lowest measure value of about 45,000 cells/mL, which is equivalent to about (10 µg-C glucose/L). The BGP method was applied in two full-scale SWRO plants that included (i) dissolved air flotation (DAF) and ultra-filtration (UF); (ii) dual-media filtration (DMF) and cartridge filter (CF), which were compared with the cleaning frequency of the plants. A significant reduction (54%) in BGP was observed through DAF–UF as pre-treatment (with 0.5 mg Fe3+/L), while there was a 40% reduction by DMF–CF (with 0.8 mg Fe3+/L). In terms of the absolute number, the SWRO feed water after DAF–UF supports 1.5 × 106 cells/mL, which is 1.25 times higher than after DMF–CF. This corresponds to the higher cleaning-in-place (CIP) frequency of SWRO with DAF–UF compared to DMF–CF as pre-treatment, indicating that the BGP method has an added value in monitoring the biofouling potential in SWRO systems.

STUDY OF AN OILY WATER TREATMENT PROCESS IN A PILOT HYBRID SYSTEM COMBINING AIR FLOTATION AND A CONSTRUCTED WETLAND: DATA ANALYSIS, EFFICIENCY OPTIMIZATION AND SCALE-UP

In this study, we developed a hybrid system for the treatment of oily water composed of two pilot-scale prototypes combining physicochemical and biological separation methods. Oily water flowed through a dissolved air flotation (DAF) prototype in the first step. At the exit of this prototype, part of the water was saturated with atmospheric air and sent back into the DAF chamber with the aid of a centrifuge pump and the injection of microbubbles. The other part of the treated water fed a constructed wetland prototype involving floating macrophytes of the species Eichhornia crassipes. With the aid of a central composite rotatable design (CCRD, with two operating parameters) and the response surface methodology (RSM), a predictive statistical model was created for the operating conditions associated with an optimal oil-water separation efficiency of around 97% of the initial concentration of 120 ppm of oil, which is much higher than the concentration permitted by environmental legislation in Brazil (20 ppm). The efficiency results are discussed and interpreted based on the phenomena of physical and mechanical liquid particles. The combination of DAF and constructed wetland methods for oily water treatment without the addition of a coagulant/flocculant agent achieved quite satisfactory results and proved to be an eco-friendly technology. Hydraulic similarity laws were used to obtain scale-up correlations for designing the size of pilot plant equipment for the treatment of oily water with the proposed hybrid process.

A study on the feasibility and mechanism of enhanced co-coagulation dissolved air flotation with chitosan-modified microbubbles

Water from the Yellow River reservoir is treated by dissolved air flotation (DAF), but the flocs formed are loose and easily desorbed. To solve this problem, a new air flotation process, i.e., Posi-co-coagulation dissolved air flotation (Posi-CCDAF), was developed by combining DAF with microbubble surface modification technology. The feasibility of the Posi-CCDAF process was verified by using chitosan to modify the surfaces of the microbubbles. The optimal dosage ratio of chitosan/coagulant was 0.4, and the optimal pH of the reflux water was 6.00. The removal characteristics of organic pollutants under the optimal conditions were studied. The removal characteristics of natural organic matter (NOM) with different molecular weights before and after adding chitosan were compared, and the removal efficiency of disinfection byproduct precursors was evaluated. Microscopic analysis was used to observe the bubble floc adhesion process and flocs during the copolymerization process before and after the addition of chitosan. The results showed that chitosan promoted the removal of hydrophobic macromolecular organics and the trihalomethane formation potential (THMFP) by CCDAF. On the one hand, the surface of modified microbubbles in Posi-CCDAF was positively charged, which provided electrostatic force to enhance the adhesion of flocs during polymerization; on the other hand, the combination of chitosan and macromolecular organics in water formed a capture network, which made the bubble flocs larger and caused them to adhere tightly, improving the removal effect of air flotation.

Harvesting of Microcystis Flos-Aquae Using Dissolved Air Flotation: The Inhibitory Effect of Carboxyl Groups in Uronic Acid-Containing Carbohydrates

Harvesting of Microcystis Flos-Aquae Using Dissolved Air Flotation: The Inhibitory Effect of Carboxyl Groups in Uronic Acid-Containing Carbohydrates

Sequential Design of Experiments for Removal of Methylene Blue Dye by Electrocoagulation Associated with Dissolved-Air System

The present work presents a strategic sequential experimental planning to evaluate the removal of methylene blue dye from aqueous medium by electrocoagulation combined with dissolved air flotation. Effect of electrode pairs, electrode spacing, contact time, initial pH, voltage, and pressure were optimized according to the following response variables: color, final pH, turbidity, and dye removal. The best-achieved optimized conditions were: 4 pairs of electrodes, 2.5 cm spacing, electrolysis time of 203 min, initial pH 4, voltage of 32 V, and no pressure by dissolved air injection. Among the experimental results, it was possible to obtain a maximum removal of 95.1% of the dye. The analysis of the response surfaces showed that the initial pH has a great influence on the final characteristic of the treated effluent. Through the study of optimization, synthetic effluents have been obtained that meet the discharge standards according to the current Brazilian environmental legislation.

Anaerobic digestion of dissolved air floatation slurries: Effect of substrate concentration and pH

Dissolved air floatation (DAF) slurries are an unconventional substrate for anaerobic digestion owing to their high COD concentrations, mainly consisting of lipids. Batch anaerobic digestion of DAF slurry was conducted to investigate the methane production through dilution of the slurry (with mineral salt medium, MSM) and by adjusting the initial pH (to 6.0, 5.5, 5.0 and 4.5) The performance of two different inocula, namely waste activated sludge (WAS) treating domestic wastewater and anaerobic granular sludge (AGS) treating dairy wastewater, was compared. The DAF slurry had a pH of 7.03 ( ± 0.07), conductivity of 6.69 ( ± 0.54) mS/cm, and a COD and ammonium concentration of 85.96 ( ± 8.32) g/L and 168.49 ( ± 1.79) mg N/L, respectively. DAF slurry without dilution produced a maximum methane yield of 58.60 ( ± 1.97) mL/g COD after 30 days of incubation. Dilution with MSM up to three folds, improved the methane yield by about 67%–105% and 67%–177% with WAS and AGS as the inoculum, respectively. Higher methane productivity was achieved at an inoculum to substrate ratio of at least 1.5 for WAS and 2.0 for AGS, respectively. AGS was more effective with a 20% increase in methane production from 3-fold diluted DAF slurry when compared with WAS. Adjustment of the initial pH of the DAF slurry to 6.0 resulted in a methane yield of 359.71 ( ± 32.72) mL/g COD, which was 23% higher than the control without pH adjustment. This study demonstrated that the methane yield from DAF slurries can be enhanced through substrate dilution and initial pH adjustment. • Methane yield enhanced by 23% upon adjustment of initial pH of the DAF slurry to 6.0. • 3-fold dilution increased methane production rate by 275% with granular sludge. • Anaerobic granular sludge is an efficient inoculum for methanogenesis of DAF slurry. • Lag phase duration was not shortened by dilution or pH adjustment of the DAF slurry. • Optimal inoculum to substrate ratio at least 1.5 and 2.0 for WAS and AGS, respectively.

Modelling of Fat Oil and Grease (FOG) and Total Suspended Solid (TSS) Removal Rate on Dissolved Air Flotation Process Using Multiple Linear Regression

In the wastewater treatment process, floatation unit have been developed to remove particles or flocs that tend to be difficult to settle, such as fat oil and grease (FOG) and total suspended solids (TSS). Flotation is a unit operation that can separate the liquid phase or solid phase from the liquid phase, this can occur due to the presence of saturated air which is mixed so that it contains fine air bubbles that can help particles or flocs to be separated. This research was conducted by treating industrial area waste water using the flotation method with a pilot plant system. In order to work optimally, there are important parameters in the flotation process, such as debit and recirculation. This study aims to model the removal rate in FOG and TSS in the flotation process with multiple linear regression. From the modeling results, there are two models of FOG and TSS removal rate separately. R square value that obtained is for FOG and TSS removal rate is 0.678 and 0.214 consecutively.

Biodegradable methacrylated casein for cardiac tissue engineering applications.

Casein is a naturally derived amino group (-NH2) rich protein, that enables surface functionalization leading to hydrophilicity, which in turn facilitates better cell adhesion. Casein obtained from either commercial β-casein rich skim milk (A2 milk) or dissolved air flotation (DAF) technology was tested for its potential for tissue engineering applications in a comparative study. A novel biodegradable biomaterial was synthesized from casein by chemically modifying with methacrylic anhydride (MA) and combined with polyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP) blend. The resulting methacrylated casein (CasMA) with the two polymers was processed into porous scaffolds with low and high MA concentrations to demonstrate CasMA's ease of modification and reproducibility. Fourier Transform Infrared Microscopy (FTIR) and Proton Nuclear Magnetic Resonance (1H NMR) revealed the presence of all the components and the successful modification of casein. The rheological and morphological analysis presented viscous behaviour and columnar hollow tube-like microstructures in agreement with the biomaterials' swelling and biodegradation behaviour. The live/dead in vitro assay showed high cell viability that agreed with the cell proliferation (MTT) assay in vitro, which indicated increased proliferation upon casein modification at appropriate biomaterial concentrations and volumes. This study not only showed a possible mechanism of casein methacrylation but also presented the potential use of waste materials like DAF-casein as a value-added product for tissue engineering applications.

Chocolate industry side streams as a valuable feedstock for microbial long-chain dicarboxylic acid production

Two high-fat containing side streams from the chocolate industry were evaluated as an alternative renewable substrate for biochemical long-chain dicarboxylic acid (DCA) production by Candida tropicalis. Cleaning water from liquid chocolate transport and dissolved air flotation (DAF) sludge from the wastewater treatment plant contained 29 and 18 m% fat respectively. The addition of up to 100 g.L−1 of the ‘chocolate water’ and 80 % (v/v) of DAF sludge had no negative effects on both growth and DCA production. In a fed-batch reactor, a DCA concentration of 5.8 g.L−1 was obtained after 120 h and 47.5 % of the consumed fats were converted to DCA upon glucose addition when using chocolate water. Using DAF sludge, a DCA concentration of 4.9 g.L−1 was obtained after 72 h, equalling 37.5 % of the consumed fats. This research shows the potential of the researched side streams as a substrate for DCA production.

Understanding variability in algal solid-liquid separation process outcomes by manipulating extracellular protein-carbohydrate interactions

Coagulation-flocculation followed by sedimentation or dissolved air flotation (DAF) are processes routinely used for separating microalgae from water; however, during algae separation then can exhibit inconsistent separation, high coagulant demand, and high operating cost. To circumvent these problems, previous studies reported the development of a novel DAF process in which bubbles were modified instead of particles. While this process was shown to be sustainable and inexpensive, the problem of inconsistent algal separation across species remained. Recent research has suggested that this could be due to the varying concentration and character of algal-derived proteins and carbohydrates within the extracellular organic matter (EOM) and their associated interactions. This hypothesis is tested in the current study using the novel modified-bubble DAF process, which has been highly susceptible to EOM protein and carbohydrate concentrations and character. Biomolecular additives (commercially available proteins and carbohydrates, and algal-extracted proteins) of widely differing molecular weight (MW) and charge were dosed in varying proportions into samples containing either Chlorella vulgaris CS-42/7, Microcystis aeruginosa CS-564/01, or Microcystis aeruginosa CS-555/1 after removing the intrinsic EOM. These cell-rich suspensions were then subject to flotation using cationic bubbles modified with poly(diallyldimethylammonium chloride) (PDADMAC). When additives were dosed independently, separation increased from <5% to up to 62%. The maximum separation was obtained when the dose was double the respective biopolymer concentration measured in the intrinsic EOM for the equivalent species, and, in the case of protein additives, when MW and charge were >50 kDa, and >0.5 meq·g-1, respectively, irrespective of the species tested. When evaluating steric- and charge-based protein-carbohydrate interactions on cell separation by simultaneously dosing high MW and high charge protein- and carbohydrate-additives, enhanced separation of up to 79% was achieved. It is suggested that enhanced cell separation is achieved due to proteins and carbohydrates bridging with cells and forming protein-carbohydrate-cell suprastructures in the presence of a flocculant, e.g. PDADMAC, and this only occurs when the intrinsic EOM comprises proteins and carbohydrates that have high MW (>25 kDa) and charge (>0.2 meq·g-1), and interactions with each other and with the cell surface.

The removal efficiency and mechanism of microplastic enhancement by positive modification dissolved air flotation.

Microplastics (MPs) are widely distributed in freshwater and have the following characteristics: small size, strong hydrophobicity, difficult degradation, and easy adsorption of toxic substances. These characteristics pose a potential threat to the environment and human health. In this paper, three common MPs in freshwater were removed by conventional dissolved air flotation (DAF) and positive modification DAF (Posi-DAF). The results showed that the optimal removal efficiency of MPs by conventional DAF was 32%-38% at 0.4-0.5MPa. This indicated that the adhesion between microbubbles (MBs) and MPs was not ideal when the hydrophilic/hydrophobic interaction was the dominant mechanism. However, the removal efficiency of MPs was increased by 13.6%-33.7% compared with that of conventional DAF after two surface modifiers were used on MBs. This result indicated that in addition to the hydrophilic/hydrophobic interaction, both charge attraction and sweeping had positive effects. PRACTITIONER POINTS: The removal efficiency and mechanism of MPs by posi-DAF were investigated. The characteristics, particle number, and adhesion of microplastics were measured. Conventional DAF was dominated by hydrophilic/hydrophobic interactions. CTAB Posi-DAF was dominated by charge attraction. PDADMAC Posi-DAF was dominated by charge attraction and sweeping.

Automatic control of coagulant dosage on the sedimentation and dissolved air flotation(SeDAF) process for enhanced phosphorus removal in sewage treatment facilities

Automatic control of coagulant dosage on the sedimentation and dissolved air flotation(SeDAF) process for enhanced phosphorus removal in sewage treatment facilities

Large batch bench-scale dissolved air flotation system for simulating full-scale turbidity removal

ABSTRACT One of the expected outcomes of global warming is increased algal and cyanobacterial blooms. Based on its ability to separate algal particles, dissolved air flotation (DAF) is considered as a climate change adaptation technology for water treatment. The feasibility of DAF treatment is often assessed using DAF jar tests; however, they are not particularly good at predicting a full-scale DAF system’s turbidity removals. Therefore, our group has developed a more reliable larger-diameter/larger-volume batch apparatus (LB-DAF), which was optimized by comparison with a full-scale DAF plant treating a low turbidity, highly coloured river water (SUVA ∼ 4.3). The objective of this study was to verify that the LB-DAF was capable of simulating full-scale DAF systems treating two significantly different waters. One was water from a large eutrophic bay in Lake Ontario (SUVA ∼2.6) and the second was a river water (SUVA ∼3.5). The turbidity removals achieved by the full-scale DAF systems treating these waters were compared with those for the LB-DAF tests conducted using different flocculation velocity gradients, saturated water pressures, recycle ratios and water depth to diameter ratios. The LB-DAF tests are good predictors of the full-scale DAF turbidity removals, the average difference for the two waters tested were 2% and 6%. The LB-DAF natural organic matter (NOM) removals for both waters differed by less than 1% from that measured at the corresponding treatment plants. In addition, as in our previous LB-DAF study, varying the different LB-DAF operational variables did not have a significant impact on turbidity and NOM removals.

Sludge Production Characteristics of SedimentationㆍDissolved Air Flotation (SeDAF) Process for Enhanced Phosphorus Removal

Objectives : In order to prevent eutrophication and algal blooms, Ministry of Environment in Korea reinforced the effluent standards of wastewater treatment facilities. As a result, many advanced wastewater treatment processes have been implemented nationwide. Current conventional treatment systems have usually been facing high operational costs and large sludge production problems. Therefore, it is essential to develop more economic and efficient process to cope with these issues.Methods : The sedimentation and dissolved air flotation (SeDAF) process has been developed, that integrates sedimentation and dissolved air flotation. Several simulation experiments were carried out to verify and optimize the operation conditions of the SeDAF process. Removal efficiencies of each water quality item and sludge mass balance were analyzed intensively in the SeDAF process using the modified jar-test.Results and Discussion : Removal efficiencies of the SeDAF process were higher and more stable than those of sedimentation process. Several ‘sludge production / coagulant dosage’ ratios were analyzed and the representative value of 4 mg･L-1 as SS / mg･L-1 as Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; was obtained in the SeDAF process. Fractions of suspended solids (SS) and total phosphorus (T-P) in sludge were measured; the ratios of flotation sludge to sedimentation sludge and fractions of flotation sludge in total sludge had their typical convergence ranges for the conditions of optimal coagulant dosage.Conclusions : The ratios or fractions of SS and T-P in sludge could be applied as the evaluation indicators of the SeDAF process. The reduction of coagulant dosage could be corresponded directly to the reduction of sludge production.

Applicability of Al/P (Aluminium/Phosphorus) Ratio in SeDAF Process for Enhanced Phosphorus Removal

Objectives : To prevent eutrophication and algal blooms, Ministry of Environment in Korea has reinforced the effluent standards of wastewater treatment facilities. In the last 20 years, various advanced wastewater treatment processes have been introduced nationwide. The sedimentation･dissolved air flotation (SeDAF) process has been developed for efficient enhanced phosphorus removal in the previous researches. In the study, several factors were reviewed to examine the operation characteristics of the SeDAF process. In particular, the applicability of aluminium/phosphorus (Al/P) and aluminium/turbidity (Al/T) ratios were investigated intensively.Methods : To derive the appropriate operating conditions for the SeDAF process, several sets of lab-scale tests were carried out. For each operating condition, Al/P (Al/T-P), Al/PO&lt;sub&gt;4&lt;/sub&gt;3--P, and Al/T (Al/Turbidity) ratios were analyzed, compared and reviewed respectively.Results and Discussion : Al/P ratio was revealed as the most prominent factor in terms of stability and feasibility of operation, and Al/P values of the SeDAF process could achieve lower values than those of other processes in the previous researches.Conclusions : It could be expected that the coagulant dosage decision using Al/P ratio has many advantages to reduce coagulant dosage and to decrease the amount of sludge production in the SeDAF process.

Monitoring Biofouling Potential Using ATP-Based Bacterial Growth Potential in SWRO Pre-Treatment of a Full-Scale Plant.

Several potential growth methods have been developed to monitor biological/organic fouling potential in seawater reverse osmosis (SWRO), but to date the correlation between these methods and biofouling of SWRO has not been demonstrated. In this research, the relation between a new adenosine triphosphate (ATP)-based bacterial growth potential (BGP) test of SWRO feed water and SWRO membrane performance is investigated. For this purpose, the pre-treatment of a full-scale SWRO plant including dissolved air flotation (DAF) and two stage dual media filtration (DMF) was monitored for 5 months using BGP, orthophosphate, organic fractions by liquid chromatography coupled with organic carbon detection (LC-OCD), silt density index (SDI), and modified fouling index (MFI). Results showed that particulate fouling potential was well controlled through the SWRO pre-treatment as the measured SDI and MFI in the SWRO feed water were below the recommended values. DAF in combination with coagulation (1–5 mg-Fe3+/L) consistently achieved 70% removal of orthophosphate, 50% removal of BGP, 25% removal of biopolymers, and 10% removal of humic substances. Higher BGP (100–950 µg-C/L) in the SWRO feed water corresponded to a higher normalized pressure drop in the SWRO, suggesting the applicability of using BGP as a biofouling indicator in SWRO systems. However, to validate this conclusion, more SWRO plants with different pre-treatment systems need to be monitored for longer periods of time.

The impact of dosing sequence on the removal of the persistent pesticide metaldehyde using powdered activated carbon with coagulation and clarification

Removal of pesticides from drinking water remains a challenge for water treatment suppliers throughout the world. A combined treatment of dissolved air flotation (DAF) and powdered activated carbon (PAC) was investigated as a treatment process for removal of the recalcitrant pesticide metaldehyde. The PAC dosing position relative to the coagulant was studied regarding its impact on the removal of NOM and pesticide, floc formation and the clarification efficiency. Four different water sources were spiked with the pesticide and treated using PAC. A PAC dose of 100 mg/L using a contact time of 20 min was required in order to effectively remove pesticide to the compliance concentrations for all of the water sources. The pesticide adsorption rate (kmet) decreased as the source water DOC increased, moving from 79.5–21.0 mg/μg/min with an increase in DOC from 2.6 to 6.5 mg/L. When combined with coagulation, the sequence of addition of PAC followed by coagulant was most effective due to increased incorporation of PAC into the floc, large floc size (median floc size 800 μm) and a high level of pesticide removal, reducing the metaldehyde concentration to 0.18 μg/L. Limited incorporation of PAC into flocs was observed when the adsorbent was added after the coagulant. The results provide a rational basis for selection of process conditions for pesticide removal using PAC and clarification.

Interactions between flocs and bubbles in the separation zone of dissolved air flotation system

The interaction between flocs and bubbles is crucial to achieve separation efficiency in the separation zone of the dissolved air flotation process. In this study, a micro-scale observation system was established to investigate the interaction between flocs and bubbles in the separation zone of the system. Four periodic interactions were observed-collision, adhesion, coalescence, and desorption (CACD). Small flocs achieved higher unit buoyancy (buoyancy per surface area) than that of large flocs. High collision probability can be obtained between bubbles and small flocs according to Stokes' law and Reynolds experiments. Simulation using Fluent indicated that low-pressure drag acting on small flocs resulted in a high probability of collision. Therefore, small flocs can capture bubbles and accumulate high enough buoyancy in a short time due to the high collision probability and low buoyancy required for small flocs to float. Moreover, the small flocs have a limited number of bubbles on the surface within such a short time, leading to a low probability of desorption and coalescence. The practical verification also show that small flocs are favorable for the high separation efficiency of the flotation process.

Removal of micropollutants from municipal wastewater using different types of activated carbons

The water reservoirs are getting polluted due to increasing amounts of micropollutants such as pharmaceuticals, organic polymers and suspended solids. Powdered activated carbon (PAC) has been proved to be a promising solution for the purification of water without having harmful impacts on the environment. Parameters such as PAC dosing, wastewater hardness, the effect of coagulant and flocculant were evaluated in a batch scale study. These parameters were further applied on a pilot plant scale for the performance evaluation of PAC based removal of micropollutants concerning the contact time and PAC dosing with main focus on recirculation of PAC sludge. The obtained optimum dose was 10–20 mg/L providing 84.40–91.30% removal efficiency of suspended solid micropollutants (MPs) and this efficiency increased to 88.90–93.00% along with coagulant which further raised by the addition of polymer and recirculation process at batch scale. On pilot plant scale, the concentration in contact reactor and PAC removal effectiveness of dissolved air flotation, lamella separator and sedimentation tank were compared. Constant optimisation resulted in a concentration ranging from 2.70 to 3.40 g/L at dosing of PAC 10 mg/L, coagulant 2.00 mg/L and polymer 0.50 mg/L. PAC doses of 10–20 mg/L with 15–30 min contact time proved best for above 70–80% elimination. The recirculation system has also proved an efficient technique because the PAC's adsorption capacity was practically completely used. Small PAC dosages yielded high micropollutants elimination.