Micro-bubble flow simulation of dissolved air flotation process for water treatment using computational fluid dynamics technique

Evaluation of a hydrodynamic cavitation-type bubble generator in a prototype bench-scale flotation unit for poultry processing wastewater treatment

Dissolved Air Flotation (DAF) systems are designed to remove oil and grease (O&G) and total suspended solids (TSS) in wastewater treatment. These systems require saturation tanks, water pumps, and high-pressure compressors to control the pressure, hydraulic retention time, and airflow parameters. DAF process efficiency depends on complex operational controls associated with these components, and the most critical aspect of an effectively operating DAF unit is a generated bubble size. This work presents the design and operational test of a flotation unit prototype that replaces the saturation tank and high-pressure compressors present in DAF with the CARMIN microbubble injector, the evaluation of the proposed system's TSS and O&G removal efficiency was carried out considering different initial configurations of the injector to change the generated microbubble size, four synthetic wastewater solutions, and poly aluminum chloride as a flocculant to establish the potential of this system for the poultry processing wastewater treatment. Mean microbubble size results were obtained from 47.41 µm to 116.17 µm. The average removal efficiency of TSS exceeded 65% under a high concentration of suspended particles (1,560 mg/l) and 80% under a lower TSS concentration (795 mg/l). Meanwhile, 70% and 90% of O&G were removed from high (400 mg/l) and low (100 mg/l) initial O&G concentrations, respectively. These removal levels are similar to those reported in the literature for DAF for poultry processing wastewater, albeit with a simple configuration and better controllability and scalability.

Three-dimensional simulation of the influence of different flotation media in the dissolved air flotation tank through the population balance model

Gas-liquid flow in the dissolved air flotation (DAF) tank was studied through computational fluid dynamics through the realizable k-ε model and the population balance model (PBM) to predict the gas content of different flotation mediums (air, carbon dioxide, and chlorine) at different heights of the separation zone in the DAF tank. Simultaneously, a particular focus was placed on studying the effects of bubble aggregation and breakage on gas content. The results indicated that there were virtually no bubbles present in the region below 0.1 m of the separation zone. The gas content in the separation zone could meet the needs for gas content in the DAF tank when all these three gases were adopted as flotation medium. The introduction of models for bubble aggregation and breakage resulted in lower gas content at the bottom of the separation zone and higher gas content at the top, aligning more closely with experimental data. Due to the structural similarity and similar physicochemical characteristics of carbon dioxide and water molecules, the impact of bubble aggregation and breakage on the gas content is minimal.

A two-stage dissolved air flotation saturator configuration for significant microbubble improvement

The presence of suspended contaminants in water and wastewater, such as algae, colloids, fats and oil, necessitates the use of systems such as dissolved air flotation (DAF) for their removal. In the current study, a novel setup has been proposed for bubble enhancement. An industrial scale (pilot) DAF system was tested at saturator pressures of 3-7 atm and flow rates of 5-20 L/min in three different configurations, namely, empty, packed, and the innovative two-stage (TS) configuration. In the TS system, after the nucleation of micro bubbles, the water is returned to the saturator to undergo pressurization for a second time before it is passed through the nozzle once more and is released. The results show that the highest volume of released air as well as the smallest microbubbles are seen in the TS configuration, followed by packed mode, with the empty configuration showing the least favourable results. Moreover, the bubbles produced at the lowest residence time and pressure (3 atm) with the novel setup are better than the bubbles produced by the standard configuration, even with pressures as high as 7 atm. Thus, the novel TS setup can allow for significantly lower energy requirements and lower capital costs. For real-world application of the TS system, the feed for the saturator could be extracted from within or near the contact zone, i.e. where the bubbles are released in the DAF tank.

Global distribution of microplastic contaminants in aquatic environments and their remediation strategies

This review describes the occurrence and distribution of microplastics in freshwater and marine environments in recent years (2017-2022). Use of microplastics often results in contamination of aquatic environments, threatens biodiversity, and creates the need for environmental remediation. Such remediation strategies can involve primary, secondary, and tertiary treatments. Tertiary treatment is a frequent research subject due to its high efficiency and the possibility for advancements and enhancements. This study discusses tertiary treatments with remediation efficiencies of 95% and greater and their advantages, disadvantages, and future perspectives. Biochar-mediated remediation of microplastics is an effective method that may be able to achieve efficiencies approaching 100%. The study concludes by exploring methods of removing microplastics, including constructed wetlands and biochar, which offer high efficiency. PRACTITIONER POINTS: Tertiary treatments are an effective microplastic remediation strategy applicable succeeding secondary or primary treatments or as an individual remediation strategy. Biochar is a highly efficient adsorbent for microplastic remediation from aquatic environment with eco-friendly aspect and reusability. Modifications in tertiary treatments and enhancement in remediation efficiency are still a subject of research for future studies.

Low-energy high-rate flotation technology for reduction of organic matter and disinfection by-products formation potential: A pilot-scale study

Despite operating complexity and high energy costs associated with its operation and maintenance, dissolved air flotation (DAF) is widely used in drinking water treatment processes. Recently, the focus has shifted to designing and developing DAF with high surface loading rates. This research compares the performance of pilot-scale high-rate DAF and low-energy high-rate flash-pressurized flotation (FPF) based on the removal behavior of natural organic matter, different molecular weight size fractions, and the formation potential of disinfection by-products. For a surface-loading rate of 30 m/h, the residual dissolved organic matter (DOC) concentrations in treated samples from high-rate DAF and FPF were 1.35 ± 0.02 (30.25 ± 0.15% removal) mg/L and 1.37 ± 0.03 (29.12 ± 1.72% removal) mg/L, respectively. In contrast, the removal of high-molecular-weight fractions, i.e., biopolymers and humic substances, showed similar removal performance for both treatment processes but not for building blocks. The removal rates were 27.10% and 6.64% for high-rate DAF and FPF, respectively. The formation potential of trihalomethanes/DOC for high-rate DAF with reaction times of 1, 3, 6, and 9 days 14.12 ± 0.18, 17.84 ± 0.22, 23.04 ± 0.29, and 29.73 ± 0.37 μg/mg C, respectively, and 16.83 ± 0.34, 22.69 ± 0.46, 27.08 ± 0.55, and 28.54 ± 0.58 for high-rate FPF. In the case of haloacetonitriles/dissolved organic nitrogen-humic substances and chloral hydrate/DOC, there were no significant differences. Thus, low-energy high-rate FPF with a reduction of energy of 55% provides an alternative to high-rate DAF.

Sustainable approach on removal of toxic metals from electroplating industrial wastewater using dissolved air flotation

This research paper concentrates on the removal of heavy metal from wastewater which was produced from an electroplating industry. Here, the Dissolved Air Flotation (DAF) treatment process is carried out to remove toxic metals such as chromium, cadmium, nickel, lead, and copper using Sodium Dodecyl Sulfate (SDS) as a collector. The best-optimized conditions for the maximum removal of all the metal ions about 97.39% was achieved at pH 8, contact time of 60 min, surfactant dosage of 0.2 g, and the pressure of 137.89 kPa. At optimized conditions, the treated water consists of 2.71 mg/L of chromium, 1.13 mg/L of cadmium, 10.24 mg/L of nickel, 0.06 mg/L of lead, and 1.14 mg/L of copper. The used surfactant SDS was found as an environmentally friendly compound as prescribed by the Environmental Protection Agency. It is inferred that the flotation kinetics that manifests the rate of recovery and time for all the metal ions follow first-order kinetics. Further, the removal rate constant (k) increases with decreasing the initial metal ion concentration. Overall, the result of this work propounds that the DAF process plays as a promising technique to eliminate noxious pollutants from the wastewater.

Numerical Investigation on the Dynamic Flow Pattern in a New Wastewater Treatment System

Currently, industries seek to optimize the development of technology from energy-saving, economic, and environmental perspectives. Dissolved air flotation (DAF) is one of the most effective wastewater treatment systems. However, it requires considerable energy and causes significant operating costs. A recently emerged application of using fluidic oscillators (FOs) to generate microbubbles has attracted extensive attention, as it consumes much less energy and has proven to be a more energy-efficient technique. In this article, a microbubble generator based on FOs is introduced into the flotation tank, and an energy-saving water treatment system, namely fluidic air flotation (FAF), is presented. Using the computational fluid dynamics (CFD) method, the flow pattern of the FAF is investigated. It is observed that FAF generates a dynamic flow pattern, which is beneficial for bubble removal. At the upper part of the separation zone, the flow pattern exhibits a wavy shape. The flow pattern at the lower part switches between clockwise and counterclockwise. The air distribution of the separation zone is also studied. It is found that the height of the “white water” zone almost linearly decreases with the increase in bubble diameter and diffuser size. FAF consumes almost no energy and occupies a small area, and it is expected to provide a promising solution to develop a new generation of the wastewater treatment system.

Hydrodynamic and Performance Evaluation of a Porous Ceramic Membrane Module Used on the Water-Oil Separation Process: An Investigation by CFD

Wastewater from the oil industry can be considered a dangerous contaminant for the environment and needs to be treated before disposal or re-use. Currently, membrane separation is one of the most used technologies for the treatment of produced water. Therefore, the present work aims to study the process of separating oily water in a module equipped with a ceramic membrane, based on the Eulerian–Eulerian approach and the Shear-Stress Transport (SST k-ω) turbulence model, using the Ansys Fluent^® 15.0. The hydrodynamic behavior of the water/oil mixture in the filtration module was evaluated under different conditions of the mass flow rate of the fluid mixture and oil concentration at the entrance, the diameter of the oil particles, and membrane permeability and porosity. It was found that an increase in the feed mass flow rate from 0.5 to 1.5 kg/s significantly influenced transmembrane pressure, that varied from 33.00 to 221.32 kPa. Besides, it was observed that the particle diameter and porosity of the membranes did not influence the performance of the filtration module; it was also verified that increasing the permeability of the membranes, from 3 × 10⁻¹⁵ to 3 × 10⁻¹³ m², caused transmembrane pressure reduction of 22.77%. The greater the average oil concentration at the permeate (from 0.021 to 0.037 kg/m³) and concentrate (from 1.00 to 1.154 kg/m³) outlets, the higher the average flow rate of oil at the permeate outlets. These results showed that the filter separator has good potential for water/oil separation.