Dissolved Air Flotation Research Articles

Assessing the efficacy of dissolved air and flash-pressurized flotations using low energy for the removal of organic precursors and disinfection byproducts: a pilot-scale study.

Dissolved air flotation (DAF) is a widely used treatment process in drinking water and wastewater treatment plants despite high energy cost associated with operation and maintenance (accounts 50% of the total annual operation cost). In recent years, the focus has been diverted to optimizing or reducing energy, and a microbubble generation without a saturator was developed and used in small treatment facilities because of its simple structure. Thus, in this study, DAF and low-energy flash-pressurized flotation (FPF) efficacies were investigated in a pilot plant based on organic precursors, different molecular weight (MW) fractions, and disinfection byproduct reduction. The organic fractions with different MW was analyzed by liquid chromatography-organic carbon detector. Both DAF (550kPa) and FPF (300kPa) showed similar removal of dissolved organic carbon (DOC) and chromatographic DOC; however, the removal tendency of different MW fractions found was different. There was no significant difference in the removal of biopolymers, building blocks, and low molecular weight (LMW) neutrals for both DAF and FPF. Interestingly, the removal of LMW acids was found to be higher (93.8%) for DAF, whereas only 35.8% removal was observed for FPF. The total trihalomethanes concentration in a DAF-treated water sample was found to be 10% lower than that of FPF. Also, the reduction in haloacetonitriles was found to be slightly higher for a water sample treated by using DAF than by using FPF (1.5 and 1.8μgL-1, respectively). Moreover, the formation of chloral hydrate was observed to be the same (1.9μgL-1) for DAF- and FPF-treated water, with a total reduction of 40.6%. FPF with low pressure enabled a reduction in energy of around 55% when compared with DAF. Thus, FPF with low-pressure energy provides an alternative to DAF by reducing the annual operation cost and carbon footprint.

Flocculation and Flotation to Recover Protein-Enriched Biomasses from Shrimp Boiling and Peeling Process Waters: A Case Study

A novel integrated process for the recovery of protein-enriched biomasses from shrimp boiling water (SBW) and shrimp peeling water (SPW) was investigated by combining flocculation (F) and dissolved air flotation (DAF) into an F-DAF process. Alginate and carrageenan were used as flocculants. It was found that the protein yield from SPW and SBW in the F-DAF process was 68-97% and 26-45%, respectively. This led to a reduction in protein content of the influent SBW and SPW (12.4 and 1.4 g/L, respectively) by up to 76% and 85%, resulting in outlets with 2.9 and 0.2 g/L protein, respectively. Further, the F-DAF recovery process concentrated the proteins of SBW and SPW up to 7 and 29 times, respectively, thus, generating a protein-enriched biomass. After spray drying, biomass from SBW had up to 61% proteins and out of the total amino acids, up to 47% were essential ones. Further, the spray dried powder contained up to 23% total lipids, 2.7% long chained n-3 polyunsaturated fatty acids and 49.7 mg/g total astaxanthin. The studied F-DAF recovery system can thus be successfully used for recovering nutrients from process waters generated during the production of peeled shrimps.

Refractory oil wastewater treatment by dissolved air flotation, electrochemical advanced oxidation process, and magnetic biochar integrated system

Petrochemical and food processing industries generate environmentally hazardous wastewaters that contain oil, volatile organic compounds (VOCs), and heavy metals. Such non-biodegradable contaminants require a complicated treatment process before disposal owing to their heterogeneous components. However, the conventional treatment process has relatively low removal efficiency and produces secondary pollutants. Here, we developed a hybrid treatment system with a high removal efficiency of suspended solids (SS), VOCs, and heavy metals during the pre-, main-, and post-treatment steps, respectively. In the pretreatment, dissolved air flotation with a modified slit nozzle, which generates size-tunable micro/nano-sized bubbles, removed 93.5% of the chemical oxygen demand (COD). The increase in the size of the bubbles in the range of 2–20 μm led to the effective removal of oil particles with a size comparable to that of the bubbles even with a low amount of coagulant. In the main treatment process, VOCs were degraded by an electrochemical advanced oxidation process (EAOP). Boron-doped diamond (BDD) electrodes were capable of degrading the non-degradable compounds 1, 4-dioxane, dichloromethane and tetrachloroethylene without generating sludge, compared to the low removal efficiency of the single and composite catalyst-doped dimensionally stable anodes. Due to the wide potential window, BDD was capable of generating hydroxyl radical. Such strong oxidant was the main factor in the high degradation efficiency. The environmentally friendly hybrid system was applied to the food and laundry wastewater treatment. In the pretreatment process, 99.7% of the oil was removed, and 95% of the COD was removed by the dual BDD–DSA electrodes in the EAOP. In the post-treatment process, more than 90% of heavy metals, including Cu, As, and Pb, were removed by a magnetic biochar adsorption process, and 90% of the biochar was recovered after the process.

High air flotation efficiency of multiphase flow pump with the addition of dodecyl dimethyl benzyl ammonium chloride (DDBAC)

Abstract Recently, centrifugal multiphase pump–dissolved air flotation (CMP-DAF) has become an increasingly popular alternative to DAF that can achieve more stable performance and higher removal efficiency, and this method is widely used in sewage treatment. However, the nonuniformity of the bubble size and low adherence of the floc particles and bubbles, as well as the complicated raw water quality, pose great challenges to CMP-DAF, which does not meet the standards of water supply and drainage in practical use. In the present study, the surfactant dodecyl dimethyl benzyl ammonium chloride (DDBAC) was utilized as a flotation agent to further improve the flotation efficiency of the CMP-DAF process. DDBAC at a dosage of 0.2 mg/L was introduced to the air flotation of raw water to construct a flotation enhanced CMP air flotation system. The results showed that the average turbidity decreased to 0.433 ± 0.017 NTU, and effluent floc particles were present at 1,053 cnt/mL with an acceptable removal rate of 96.20%. In addition, 34.0% and 30.1% of UV254 and CODMn were removed, respectively. These results imply that DDBAC can increase the collision efficiency of bubble particles by reducing the diameter of the bubbles, which is conducive to forming larger flocs, and enhancing the shear resistance of the bubble–floc particles, thus improving the air flotation efficiency.

Effluent conditioning of biodiesel production for biological treatment using clay as a separation coadjutant

Biodiesel is a renewable, non-toxic and sustainable biofuel, considered to be the main candidate for a fossil fuel alternative in many countries. However, its manufacturing process results in about 0.2 to 3 L of effluent per litre of biodiesel produced. In addition to an inherently high organic load, its composition includes by-products, traces of unreacted chemicals and catalysts, which inhibit microorganism growth and prevent its direct treatment by tertiary methods. In this context, this work aims to evaluate the combination of the coagulation-flocculation technique with dissolved air flotation (DAF). Real wastewater samples were obtained by synthesising biodiesel from soybean oil in-loco and performing the required washing procedures. The highest turbidity reduction efficiency (92.03%) was obtained using 1200 of clay. By using response surface methodology, it was possible to analyse the effect of the chosen experimental factors and show that the best results (81.28%, 58.95% and 89.34% for turbidity, oil and grease and chemical oxygen demand - respectively) were obtained using 925 of clay and 1000 of coagulant. Ultimately, clay proved to be an efficient coadjutant in the removal of organic matter, oils, grease, suspended solids and soluble organic matter from the biodiesel wastewater. Moreover, its low cost over traditional flocculants makes it an attractive alternative to industrial wastewater treatment processes.

Life cycle assessment of wastewater reclamation in a petroleum refinery in Turkey

Wastewater reclamation in a petroleum refinery in Turkey was evaluated with life cycle assessment (LCA). The goal of the study was to determine whether or not refinery wastewater reclamation for different industrial purposes, namely boiler feedwater, cooling water and fire water, leads to an overall benefit across different environmental aspects, besides alleviating freshwater resources, when compared to current wastewater disposal practices. The basis for the assessment was the hypothetical scale-up of a demonstration plant tested with real wastewaters from November 2018 to May 2019 at the Izmit petroleum refinery operated by Tüpraş. This demonstration plant consisted of different treatment modules, including dissolved air flotation, ceramic membrane bioreactor, catalytic wet-air oxidation, advanced oxidation with ozone and hydrogen peroxide, and reverse osmosis. The LCA was conducted following consequential modelling principles, and six environmental indicators were analysed in detail at midpoint level: global warming, respiratory inorganics, marine ecotoxicity, aquatic eutrophication, freshwater consumption and non-renewable energy demand. All three reclamation scenarios (boiler, cooling, fire water) succeeded in achieving a life-cycle freshwater saving, of around 1 m3 freshwater saved per m3 refinery wastewater. Beneficial results were also obtained in marine ecotoxicity and aquatic eutrophication, where impact is reduced up to 90% and 84%, respectively. With regard to global warming and non-renewable energy demand, only the boiler feedwater application appeared to involve an improvement over wastewater disposal, showing a net reduction of 2.2 kg CO2-eq and 40 MJ per m3 wastewater, respectively, thanks to potential thermal energy savings. For cooling makeup water and fire water, impacts were between 2 and 2.5 times higher in these two indicators when compared to wastewater disposal. Finally, the indicator on respiratory inorganic effects, showed higher impact, by a factor 2 to 7, for all reuse scenarios, due to electricity demand, which is linked to the Turkish electricity production mix with a substantial contribution from coal power plants. Thus, the results reflect that achieving a product water of very high quality comes at the price of a high energy demand. Nevertheless, A sensitivity analysis shows that the environmental performance of all scenarios would improve to a great extent when shifting to an electricity mix with a higher share of renewables, as is the current trend in most European countries.

Improving energy efficiency of pretreatment for seawater desalination during algal blooms using a novel meshed tube filtration process

A new meshed tube filtration (MTF) process was developed and assessed as a low energy-consuming pretreatment process that withstands algal blooms (i.e., red tide). This process can potentially replace the dissolved air flotation (DAF) process in typical seawater reverse osmosis (SWRO) desalination plants. Two marine microalgae species, namely C. polykrikoides and T. suecica, were first cultivated and then utilized to simulate algal bloom conditions in the lab-scale filtration experiments. The algal matter was coagulated and circulated by aeration in the MTF system that was filled with cylindrical polypropylene meshed tubes with ciliary ends and had the ability to capture coagulated algae in an effective manner. The efficiency of the MTF process to remove algal cells was significantly enhanced by optimizing the coagulant dose and the aeration rate. In order to further verify the MTF performance, DAF experiments were conducted, under similar conditions, for the comparison of algal removal effectiveness and energy consumption rates. The results showed high removal rates of algal cells as well as turbidity for MTF, although only a limited reduction of algal organic matter (AOM) was observed. When DAF was operated at energy consumption levels equivalent to MTF, its algae removal rate was lower than that of MTF. Furthermore, under optimal operating conditions, MTF consumed approximately one-third of the energy needed for DAF operation, mainly due to the fact that MTF requires less aeration. For future improvements in the AOM removal process, an energy-efficient pretreatment process could be realized for SWRO desalination facilities facing potential algal blooms.

Dissolved air flotation optimization for treatment of dairy effluents with organic coagulants

The objective of this work was to optimize the conditions of dairy effluent treatment by dissolved air flotation (DAF) at the chemically assisted primary treatment level using the combined polyacrylamide (PAM) and Tanfloc coagulants. For this, the effect of coagulant dosing and pH on the effluent turbidity removal was studied using a central composite rotatable design (CCRD). Synthetic wastewater was used in the optimization phase, and after optimization, the system was used to treat real dairy wastewater in order to determine the pollutant removal efficiency. Coagulation and flocculation tests were performed in jar test equipment and flotation in a flotastest, whose operating conditions were optimized. The results were excellent with respect to turbidity, obtaining removal efficiency above 90 % for most treatments. The regression model obtained was quadratic and significant at 5 % probability, whose R² was 97.41 %. The model has been validated and can be used for predictive purposes. The optimum point for turbidity removal was with 758.3 mg L−1 of PAM combined with 205.4 mg L−1 of Tanfloc at pH 7.6. Expressive reductions in solids, organic matter, nutrients, oils, and greases were achieved when the system was employed for treatment of real dairy wastewater.

Assessing the potential of enhanced primary clarification to manage fats, oils and grease (FOG) at wastewater treatment works

Daily, sewage treatment works (STWs) receive large volumes of fats, oils and greases (FOG), by-products of food preparation. To increase FOG removal at STW, conventional primary sedimentation tanks (PSTs) can be enhanced using chemical coagulant or through dissolved air flotation (DAF) techniques. This work aimed to assess the potential benefits of enhanced primary treatment for FOG removal through an energy and costs analysis. To achieve this, a five-year sampling programme was conducted monthly at 15 STWs measuring FOG concentrations in crude and settled sewage (i.e. after primary treatment). In addition, two DAF pilot systems were trialled for four months and their performance, in terms of FOG removal, was assessed and compared to that of a control primary clarifier. Across the 15 STWs, influent FOG concentrations were found at 57 ± 11 mg.L−1. Chemical coagulants dosed prior to PSTs increased FOG removal rates on average to 71% whilst traditional sedimentation only achieved 50% removal. Effluent FOG concentrations were found between 12–22 mg.L−1 and 19–36 mg.L−1 respectively. By contrast, DAF achieved FOG effluent concentrations on average at 10 ± 4 mg.L−1 corresponding to 74% removal from a relatively low influent concentration of 40 ± 30 mg.L−1. Thus, enhanced primary treatments have the potential to reduce organic load to secondary treatment and increase energy generation through anaerobic digestion. The overall net energy balance was estimated at 2269 MWh.year−1 for the DAF compared to 3445 MWh.year−1 for the chemically-enhanced PST making it a less financially attractive alternative. Yet, in the case where the works require upgrading to accommodate flow or load increases, DAF appeared as a sensible option over sedimentation offering significantly lower capital costs and footprint. In relation to FOG management, upgrading all STWs is not realistic and will require understanding where the benefits would be the highest.

Simulation and control of dissolved air flotation and column froth flotation with simultaneous sedimentation.

Flotation is a separation process where particles or droplets are removed from a suspension with the aid of floating gas bubbles. Applications include dissolved air flotation (DAF) in industrial wastewater treatment and column froth flotation (CFF) in wastewater treatment and mineral processing. One-dimensional models of flotation have been limited to steady-state situations for half a century by means of the drift-flux theory. A newly developed dynamic one-dimensional model formulated in terms of partial differential equations can be used to predict the process of simultaneous flotation of bubbles and sedimentation of particles that are not attached to bubbles. The governing model is a pair of first-order conservation laws for the aggregate and solids volume fractions as functions of height and time. An analysis of nonlinear ingredients of the governing equations helps to identify desired steady-state operating conditions. These can be chosen by means of operating charts, which are diagrams that visualize regions of admissible values of the volumetric flows of the feed input and underflow outlet. This is detailed for the DAF thickening process. Dynamic simulations are obtained with a recently developed numerical method. Responses to control actions are demonstrated with scenarios in CFF and DAF.

Estimation of biogas co-production potential from liquid dairy manure, dissolved air flotation waste (DAF) and dry poultry manure using biochemical methane potential (BMP) assay

Abstract Optimized biogas output and operational stability of farm-based anaerobic digester (AD) systems depends on substrate availability and quality. Economic and environmental performance is enhanced by using locally available off-farm co-substrates that have the potential to improve biogas output, but may cause inhibition or toxicity in the co-digestion process. To that end, biochemical methane potential (BMP) of liquid dairy manure (LDM) with solid poultry manure (SPM) and dissolved air flotation waste (DAF) was evaluated in a 62-day assay. Specific methane yield (SMY) ranged from 236 to 398 ml CH4·g VS-1, with up to 25% and 161% increase in biogas output from LDM and SPM, respectively, in co-digestion compared to monosubstrates only. However, indications of inhibition or beginning toxicity that merit further study, at higher levels of LDM and DAF were likely due to inhibitors in the digestion process from high free ammonia (NH4 or NH3) content from SPM, or the long chain fatty acid (LCFA) content of DAF. Findings in this study suggest opportunity in value added and environmentally sound recycling of low grade off-farm waste as AD feedstock in farm ADs while maintaining operational stability. The study expands on the use of marginal waste that may be the only regionally available source of substrate.

Petroleum Hydrocarbon Removal from Wastewaters: A Review

Oil pollutants, due to their toxicity, mutagenicity, and carcinogenicity, are considered a serious threat to human health and the environment. Petroleum hydrocarbons compounds, for instance, benzene, toluene, ethylbenzene, xylene, are among the natural compounds of crude oil and petrol and are often found in surface and underground water as a result of industrial activities, especially the handling of petrochemicals, reservoir leakage or inappropriate waste disposal processes. Methods based on the conventional wastewater treatment processes are not able to effectively eliminate oil compounds, and the high concentrations of these pollutants, as well as active sludge, may affect the activities and normal efficiency of the refinery. The methods of removal should not involve the production of harmful secondary pollutants in addition to wastewater at the level allowed for discharge into the environment. The output of sewage filtration by coagulation and dissolved air flotation (DAF) flocculation can be transferred to a biological reactor for further purification. Advanced coagulation methods such as electrocoagulation and flocculation are more advanced than conventional physical and chemical methods, but the major disadvantages are the production of large quantities of dangerous sludge that is unrecoverable and often repelled. Physical separation methods can be used to isolate large quantities of petroleum compounds, and, in some cases, these compounds can be recycled with a number of processes. The great disadvantage of these methods is the high demand for energy and the high number of blockages and clogging of a number of tools and equipment used in this process. Third-party refinement can further meet the objective of water reuse using methods such as nano-filtration, reverse osmosis, and advanced oxidation. Adsorption is an emergency technology that can be applied using minerals and excellent materials using low-cost materials and adsorbents. By combining the adsorption process with one of the advanced methods, in addition to lower sludge production, the process cost can also be reduced.

Evaluating Pre- and Post-Coagulation Configuration of Dissolved Air Flotation Using Response Surface Methodology

The effects of coagulation-dissolved air flotation (DAF) process configuration was studied on oil refinery wastewater. The configuration was done in two ways: acid-coagulation-DAF (pre-treatment) and acid-DAF-coagulation (post-treatment). Two different cationic and polymeric organic coagulants were employed in this study to compare their treatability performance with the two aforementioned configurations. All the coagulants applied before the DAF were found to be effective, with over 85% more contaminant removal efficiency than their post-treatment. Alum, being the most cost-effective coagulant, was then employed with response surface methodology (RSM) to obtain the optimum conditions. These include a coagulant dosage of 100 mg/L, air saturator pressure of 375 kPa and air–water ratio of 10% vol/vol corresponding to a desirability of 92% for the removal of oily pollutants from a local South Africa oil refinery’s wastewater. With the response quadratic models that were developed, the optimum conditions were tested experimentally, which were consistent with the models predicted results at a 95% confidence level.

Effect of coagulation and sonication on the dissolved air flotation (DAF) process for thickening of biological sludge in wastewater treatment

Background: Dissolved air floatation (DAF) is one of the methods has been used for the sludge thickening in wastewater treatment plants. This study aimed to investigate the effects of coagulation and sonication processes as additional configurations on the efficiency of a lab-scale DAF process for thickening of the biological sludge of an industrial wastewater treatment plant in Kashan, Iran. Methods: The required amounts of sludge samples were collected from a wastewater treatment plant and kept at temperature of 4°C. Variables, such as pressure (3, 5, and 7 atm), flotation time (5 and 10 minutes), ultrasonic irradiation power (0, 75, and 150 W), and presence/absence of Fe-based coagulant were considered on a sequencing batch reactor (SBR) included coagulation, flotation, and sonication processes, respectively. Results: The use of ultrasonic waves led to an insignificant increase in the DAF efficiency (P>0.05), however, the application of coagulant significantly increased the thickening efficiency (P<0.05). The maximum efficiency of the process was achieved at flotation time of 5 min, pressure of 3 atm, and sonication power of 75 W. Conclusion: According to the results, DAF has a proper efficiency for thickening of biological sludge. Coagulation compared to sonication has a greater effect on the efficiency of the process.

마이크로 부상분리 시스템을 이용한 미세먼지 오염수 처리 성능 평가

마이크로 부상분리 시스템을 이용한 미세먼지 오염수 처리 성능 평가

Advanced technologies for poultry slaughterhouse wastewater treatment: A systematic review

The current review aims at improving the understanding on the treatment frameworks related to poultry slaughterhouse wastewater (PSWW) treatment efficiency. Technologies used for nutrient and organic removal during the last 10 years are discussed in this article. The selection of specific treatment is dependent on the characteristics of wastewater, existing treatment cost, and compliance with regulations. The reverse osmosis (RO) technology, dissolved air flotation (DAF), and integrated fixed film activated sludge (IFAS) are among the technologies that can produce high-quality treated effluents. DAF is known to have the ability to remove 98.6% of biochemical oxygen demand (BOD) and 97.9% of chemical oxygen demand (COD) while RO can only remove up to 90.0% and 97.9% of total nitrogen (TN) and COD. The anaerobic sequencing batch reactor (ANSBR) technology efficiently gave 90% of TN and COD removal. However, gaps and limitations have been recognized in regards to TP removal. Advanced technologies are considered successful in terms of water recycling and reuse and waste reduction in poultry slaughterhouses that can offer a more cost-effective waste management.

Understanding the Efficiency of Aluminum Coagulants Used in Dissolved Air Flotation (DAF)

This paper reports on the efficiency of five aluminum coagulants for the treatment of a paper mill wastewater by dissolved air flotation (DAF). The coagulants studied were: alum, a polyaluminum chloride coagulant of high aluminum content and intermediate basicity (PAC-MB), another with intermediate aluminum content and high basicity (PAC-HB), a polyaluminum nitrate sulfate of intermediate aluminum content and basicity (PANS) and one hybrid coagulant formed by the combination of PANS and a mixture of polyamines (PANS-PA). The influence of Al speciation on contaminants removal and the main flocculation mechanisms involved have been analyzed. High removal of suspended solids together with significant removal of dissolved and colloidal material (COD and silica) were obtained, which is required for extended reuse of this process water. PAC-HB was the best product for removing suspended solids (85%) and soluble silica (50%) with a rather limited COD removal (5%), while PANS-PA obtained high turbidity (90%) and silica removal (45%) together with a significant soluble COD removal (15%). Monomeric Al (Ala, Alm) was more efficient in removing suspended solids and soluble COD than polymeric or colloidal Al (Alc, Alu), but the latter was more efficient in removing soluble silica. Results demonstrated that the main flocculation mechanism varies with the aluminum dosage, being predominantly charge neutralization at low dosages and sweep flocculation at high dosages. The floc strength factor however, was very high and similar for all the coagulants and dosages tested (85–90%), as it was mainly determined by the behavior of the pre-flocculated suspended solids present in wastewater. The reflocculation factor varied from 45 to 75% at the lowest dosages to almost zero at the highest dosages, confirming the transition from charge neutralization to sweep flocculation. The flocs formed by PANS-PA had lower strength than the others and it decreased with the dosage while its reflocculation factor was almost zero, even at low dosages. Due to the polyamines present in this coagulant, its flocculation mechanism is through both charge neutralization and patch formation, especially at low dosages, and sweep flocculation and interparticle bridge formation at high dosages.

Numerical simulation of dissolved air flotation using a lattice Boltzmann method.

In this paper, the behavior of a bubble and droplet rising in a system, namely, a dissolved air flotation system, is investigated under different conditions. A lattice Boltzmann model which is based on the Cahn-Hilliard equations for ternary flows is implemented. This model can handle high density and viscosity ratios, remove parasitic currents, and capture partial and total spreading conditions. Two classical problems, such as spreading of a liquid lens and the Rayleigh-Taylor instability are used to determine the accuracy of the model. As a practical application, three-component flow in a tank is studied and the dynamics of bubble and droplet under different conditions is investigated. We then concentrate on the dimensionless average velocity and locations of bubble and droplet at different density ratios, viscosity ratios, and diameter ratios. Also, total spreading and partial spreading conditions are compared. The numerical results are justifiable physically and show the ability of this model to simulate three-component flows.

Upcycling Phosphorus Recovered from Anaerobically Digested Dairy Manure to Support Production of Vegetables and Flowers

Dissolved air flotation (DAF) separates phosphorus (P)-rich fine solids from anaerobically digested dairy manure, creating opportunities to export surplus P to the marketplace as a bagged plant food product. Seedlings of tomato and marigold were amended at various volume per volume (v/v) ratios with plant foods consisting of fine solids upcycled (i.e., transformed into a higher quality product) by drying and blending with other organic residuals. A plate competition assay was conducted to assess the fine solids’ potential to suppress the plant pathogen Rhizoctonia solani. Plant foods were comprised of 2.0–2.1% N, 0.8–0.9% P and 0.6–0.8% K. Extractions indicated that plant foods contained a mixture of plant-available and slow-release P. At 6% v/v plant food, dry biomass of marigold and tomato were six-times greater than the unamended control and not significantly different from a market alternative treatment. Fine solids exhibited negligible potential to suppress R. solani. This study indicates that DAF-separated fine solids could be used to support horticulture, providing information for design of a circular economy approach to dairy manure nutrient management. Life cycle assessment and business model development for this nutrient recovery strategy are necessary next steps to further guide sustainability efforts.

Effect of salinity on air dissolution, size distribution of microbubbles, and hydrodynamics of a dissolved air flotation (DAF) system

In the present study, air dissolution, size distribution and hydrodynamics of microbubbles in a dissolved air flotation system were experimentally investigated. The amount of dissolved air was calculated by Henry’s laws of gas dissolution and compared with measured values from the liquid displacement technique. The measured air concentrations were 23.2 and 10.1 mg/l for freshwater and saline water (30 g/L), respectively, which were much lower than those calculated by Henry’s equations. Shadow imaging technique was applied to measure the size distributions of microbubbles for saline and freshwater. Whilst the size of microbubbles for freshwater were between 40–250 μm, the corresponding values for the saline water were smaller and varied between 20–160 μm. Particle image velocimetry (PIV) was also applied to map flow patterns and velocities of microbubbles for saline and freshwater. The results indicated that the flow patterns were mostly affected by the flow itself rather than the salinity and the presence of microbubbles since there was not a noticeable change between single-phase (flow without microbubbles) and two-phase flows. While the range of the velocities was between 0–64 mm/s for the freshwater, it did not exceed 48 mm/s for the saline water.