Dissolved Air Flotation Research Articles

Evaluation of pretreatment and membrane configuration for pressure-retarded osmosis application to produced water from the petroleum industry

Pressure-retarded osmosis (PRO) is a promising membrane technology for harnessing the osmotic energy of saline solutions. PRO is typically considered with seawater/river water pairings however greater energy can be recovered from hypersaline solutions including produced water (PW) from the petroleum industry. One of the major challenges facing the utilization of hypersaline PW is its high fouling propensity on membranes. In this unique experimental evaluation, real PW from different sites was pretreated to varying degrees: i) minimal, ii) intermediate, and iii) extensive. The treated effluent was subsequently used for PRO testing and fouling rates were assessed for different membrane configurations over multiple cycles. Commercial grade flat sheet (FLS) coupons and novel hollow fiber (HF) modules were compared to validate the lower fouling propensity of HF membranes in PRO application. When minimally pretreated PW (10-micron cartridge filtration (CF)) was tested in FLS mode, severe membrane fouling occurred and the PRO flux decreased by 60%. In contrast, HF modules showed <1% flux decrease under both minimal and intermediate pretreatment schemes. Extensive pretreatment (1-micron CF, dissolved air flotation (DAF), powdered activated carbon, and microfiltration) reduced FLS PRO flux decline to <1%. These results confirm that PW can be treated to suitable levels for PRO application to avoid membrane fouling. Further validation of these pretreatment methods requires long term pilot testing and techno-economic assessment.

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.

Investigation of microalgal treatment for poultry slaughterhouse wastewater after the dissolved air flotation unit

Meat and meat products are some of the primary consumption products required for the continuation of life. The world population accessed over 7.5 billion that means the demand for food is increasing every day. Slaughterhouses and integrated meat facilities are being rapidly developed and established to meet meat and meat product requirements. In slaughterhouse poultry plants, high amounts of water are utilized for the meatpacking process. The poultry slaughterhouse wastewaters contain high levels of organic solids such as fat, blood, suspended matter, and dissolved protein, which can be treated using physical, chemical, and biological treatment methods. In this study, the treatment of poultry slaughterhouse wastewater preliminarily treated by dissolved air flotation, with microalgae culture (Chlorella Vulgaris) development, unlike traditional treatments, was investigated. Chemical oxygen demand and total suspended solids parameters for wastewater treatment have been monitored for 15 days of incubation. 0.8, 4, 8, 12, and 20% by volume algae were applied for slaughterhouse wastewater, and the optimum amount of algal inoculation was determined after 15 days. When the removal efficiencies were examined, the most appropriate amount of inoculation rate with 76 % chemical oxygen demand removal and 87% algal growth (as total suspended solids) was selected as 12%.

가압펌프와 공기포화탱크를 연계한 하이브리드형 미세기포 발생장치의 운전특성

Dissolved air flotation (DAF) process has been applied to the entire environmental fields. The micro-bubble generator, which is a key facility in DAF process, can be classified according to its generation methodology. In Korea, saturator and DAF-pump types are widely utilized. The feature of saturator type is the application of an air saturation tank (AST), and it has a disadvantage in that operation and maintenance are not easy due to relatively complicated facilities. On the other hand, DAF-pump type uses a micro-bubble generating pump (MGP) alone, so the device configuration is very simple, but the ranges of optimal operating conditions are narrow. In this study, a new hybrid-type microbubble generator has been developed by linking a pressure pump and an AST by converging the advantages of the existing saturator and DAF-pump types. As a result of examining the operation characteristics of this microbubble generator including operating pressure, air flow rate, water flow rate, power consumption, A/W ratio (air/water ratio), DO, and particle size distribution, the appropriate operating conditions could be determined as operating pressure of 4.0 - 6.0 kgf/㎠, air flow rate of 4.0 - 5.0 L/min, water flow rate of 57 - 68 L/min, and A/W ratio of 5.9 - 8.7%. The average diameter of the generated microbubbles showed a stable distribution in the range of 25.0 - 26.7 μm. Based on the above results, it could be verified that the novel hybrid-type microbubble generator had excellent performance at a level that can be applied to the field.

Fast dewatering of high nanocellulose content papers with in-situ generated cationic micro-nano bubbles

Herein, an innovative method to improve the dewatering of micro- and nanofibrillated cellulose (MNFC) containing furnishes is proposed. This method is based on fiber flotation in which cationic bubbles are injected into the furnish to separate fibers from liquid medium and accumulate them on the surface of the furnish. These cationic bubbles are generated by pressurizing a solution of Hexadecyltrimethylammonium chloride in deionized water in a dissolved air flotation (DAF) tank. The drainage properties of the furnishes with MNFC content from 0% to 25% were studied. With the help of the cationic bubbles, drainage rate of 0% and 15% MNFC furnish increased from 183 ml/s to 210 ml/s and 38 ml/s to 113 ml/s, respectively. The final couch solids content of these furnishes also increased from 16 wt% to 23 wt% and from 21 wt% to 24 wt%, respectively. Cationic bubbles flocculate MNFC fibers and increase retention. Sheets characteristics including morphology, permeability, mass distribution and surface profilometry were investigated. Cationic bubbles help structure fiber elements and improve the sheet formation.

Dissolved Air Flotation to Control Phosphorus Release of Benthic Sediment in a Coastal Brackish Lake

When applying the flotation process for phosphorus (P) removal in a lake, it is important to separate as much P as possible from water bodies and sediments using microbubbles. Furthermore, for remo...

Numerical simulation on the effects of bubble size and internal structure on flow behavior in a DAF tank: A comparative study of CFD and CFD-PBM approach

Although dissolved air flotation (DAF) plays a crucial role in wastewater treatment, fluid dynamics in the contact zone (CZ) of a DAF tank are still considered black-box processes, which hampers DAF's optimal design and operation. In this article, we perform a modeling study to further unravel the governing mechanisms occurring in a DAF tank. A computational fluid dynamics (CFD) model coupled with a generic population balance model (PBM) for the DAF system was developed in this work. CFD-PBM results showed that the eddy capture is the dominating mechanism for the bubble coalescence in the most volume of the CZ. Simultaneously, the velocity gradient mechanism and turbulent induced mechanism also play a key role in bubble coalescence in the regions with drastic flow transition and in the nozzle downstream. CFD-PBM simulations reveal that increasing the recirculation rate is better than increasing the volume fraction in the smaller recirculated flow to achieve higher bubble number density and smaller bubble size if the same amount of gas flow rate is injected. The baffle with proper transverse corrugate can equalize and reduce the total coalescence rate. By establishing a synergy between fluid dynamics and bubble size to achieve the best CZ efficiency, the generic CFD-PBM approach developed in this study has laid a solid basis for the optimal design and operation of DAF systems.

Oily water treatment in a multistage tower operated under a novel induced pre-saturation process in the presence of a biosurfactant as collector

The increase in water-oil separation efficiency as a function of biosurfactant in a novel process of a continuous induced pre-saturation tower (IPST) with stages was described. The pre-saturation of the effluent in a new IPST prior to its entrance in each stage enabled enhancing the effect of the biosurfactant on the flocculation of oil droplets due to the close contact with the air during the formation of microbubbles inside a centrifuge pump. This change of a conventional dissolved-air flotation device enabled each stage to serve as a final flocculation chamber and flotation separator. The initial flocculation step occurred nearly entirely within the centrifugation pump adapted for the generation of microbubbles. Experimental tests in a bench-scale prototype of an IPST enabled drafting two operation diagrams based on the absence and presence of the biosurfactant produced by the bacterium Pseudomonas cepacia CCT 6659. We used an effluent composed of water and semi-synthetic motor oil at 500 ± 13 mg L−1. The oil removal efficiency was estimated with the aid of Damköhler numbers applied under the analogy of considering the IPST to be a set of perfect-mixture tanks in series. To quantify the increase in efficiency achieved with the addition of the biosurfactant, we identified the kinetic laws corresponding to the addition and non-addition of the biosurfactant. The addition of the biosurfactant led to an increase in the oil removal rate in the IPST from 92.5 % to 97.0 %.

Investigation of microplastic removal from greywater by coagulation and dissolved air flotation

Microplastics (MPs) have recently become a controversial issue, mainly due to their eco-toxicological effects on aquatic environments. Although a typical wastewater treatment plant (WWTP) removes a large number of MPs from the wastewaters, final effluents are yet considered to be the primary sources of MP contaminations into the environment. Hence, there should be a tertiary treatment called advanced wastewater treatment technology for efficient MP removal. In the current research, Al-based and Fe-based coagulants were used in a dissolved air flotation (DAF) cell as an advanced wastewater treatment technology to remove polyethylene (PE) MPs from greywater, which is one of the most predominant types of MPs found in the greywater. PE reduction up to 96.10 % and 70.56 % were observed for Al- and Fe-based coagulants, respectively. The operative parameters, including pressure, pH, coagulant dosage, and water flow rate into the flotation cell, were identified. The experimental design was developed using Design-Expert software to investigate and maximize the PE removal efficiency. As a result, some sufficiently accurate statistical models were proposed to obtain the optimum quantities of the respective factors. It was determined that the most effective removal was achieved with 5.95 bar saturation pressure, pH 6, 14.46 mg/L coagulant concentration, and 680.5 mL/min water flow rate into the flotation cell using AlCl3·6H2O as the coagulant.

Empirical modeling of turbidity removal in a dissolved air flotation system: application of artificial neural networks

Abstract Dissolved air flotation (DAF) is a physical separation process that uses air microbubbles to remove suspended material dispersed in a liquid phase. Even though DAF is considered a well-established unit operation, modeling it is difficult due to the complexity of the phenomena involved, resulting in conceptual models with no practical application. Thereby, the objective of this work was to evaluate empirical modeling efficiency in predicting the turbidity removal dynamic using artificial neural networks applied to a DAF prototype. For the study of the neural network input variables, a two-level, full-factorial design was utilized to verify the statistical significance of the saturation pressure and the saturated water flow rate in relation to the turbidity removal. Using a time-delay recurrent neural network architecture, two empirical models were proposed to simulate the dynamic behavior of the turbidity removal promoted by the DAF prototype. The real-time model provided good predictions with R = 0.9717 and MSE = 1.0482, and the simulation model was also able to predict the process behavior presenting performance criteria equal to R = 0.9475 and MSE = 1.8640.

Enhanced flotation technology using low-density microhollow beads to remove algae from a drinking water source

Dissolved air flotation (DAF) is a well-established flotation technology for the pretreatment of water sources with a high algal bloom. However, high shear force generated during injection of microbubbles caused breakage of floc. This study investigated the removal tendency of algae using DAF, sedimentation, and microhollow beads combined with DAF from a water sample collected from the Nakdong River in Korea. The reduction in Chl-a as algae was 8.5 ± 0.8 in DAF and 2.8 ± 0.3 mg/m3 in DAF with 90 mg/L microhollow bead. However, a further increase in the microhollow bead concentration did not show a significant difference in Chl-a reduction. For conventional DAF, the optimum flotation time was achieved in 4 min, with a removal greater than 91 %. For DAF with microhollow beads, optimum flotation time was achieved in 2 min, with a removal greater than 95.4 %. Further, for the sedimentation case, the Chl-a removal observed was 26.7 % and 87.2 % for 5- and 30-min, respectively. Different recycle ratios were tested for DAF, ranging between 5% and 15 %. The Chl-a removal achieved with 90 mg/L microhollow beads was more than 95 % for a 5% recycle ratio. Upon the addition of microhollow beads, the removal was enhanced by 23.6 % compared with DAF. Further, an increase in the recycle ratio with microhollow bead concentration did not show a significant enhancement in Chl-a removal.

Hydraulic characterization and removal of metals and nutrients in an aerated horizontal subsurface flow “racetrack” wetland treating primary-treated oil industry effluent

Constructed wetlands (CW) are an attractive technology due to their operational simplicity and low life-cycle cost. It has been applied for refinery effluent treatment but mostly single-stage designs (e.g., vertical or horizontal flow) have been tested. However, to achieve a good treatment efficiency for industrial effluents, different treatment conditions (both aerobic and anaerobic) are needed. This means that hybrid CW systems are typically required with a respectively increased area demand. In addition, a strong aerobic environment that facilitates the formation of iron, manganese, zinc and aluminum precipitates cannot be established with passive wetland systems, while the role of these oxyhydroxide compounds in the further co-precipitation and removal of heavy metals such as copper, nickel, lead, and chromium that can simplify the overall treatment of industrial wastewaters is poorly understood in CW. Therefore, this study tests for the first time an innovative CW design that combines an artificially aerated section with a non-aerated section in a single unit applied for oil refinery wastewater treatment. Four pilot units were tested with different design (i.e., planted/unplanted, aerated/non-aerated) and operational (two different hydraulic loading rates) characteristics to estimate the role of plants and artificial aeration and to identify the optimum design configuration. The pilot units received a primary refinery effluent, i.e., after passing through a dissolved air flotation unit. The first-order removal of heavy metals under aerobic conditions is evaluated, along with the removal of phenols and nutrients. High removal rates for Fe (96–98%), Mn (38–81%), Al (49–73%), and Zn (99–100%) generally as oxyhydroxide precipitates were found, while removal of Cu (61–80%), Ni (70–85%), Pb (96–99%) and Cr (60–92%) under aerobic conditions was also observed, likely through co-precipitation. Complete phenols and ammonia nitrogen removal was also found. The first-order rate coefficient (k) calculated from the collected data demonstrates that the tested CW represents an advanced wetland design reaching higher removal rates at a smaller area demand than the common CW systems.

Wastewater treatment using DAF for process water reuse in apatite flotation

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 P2O5 highest than minimum acceptable in this industry.

Degradation effect of ultraviolet-induced advanced oxidation of chlorine, chlorine dioxide, and hydrogen peroxide and its impact on coagulation of extracellular organic matter produced by Microcystis aeruginosa

Implementation of an ultraviolet (UV)-induced advanced oxidation process (AOP) before coagulation was found to enhance the removal of algae cells. However, the effect of UV-induced AOPs on extracellular cellular organic matter (EOM) and on its coagulation and removal was neglected. This study investigated the impact of UV-induced AOPs (UV/Cl2, UV/ClO2, and UV/H2O2) on EOM from Microcystis aeruginosa, and its coagulation and removal by a conventional gravity system (CGS), dissolved air flotation, and a low-energy flash-pressurized flotation (FPF) process. The changes in EOM characteristics before and after the UV-induced AOPs were based on UV absorbance (UV254) and liquid chromatography with organic carbon detection analysis. The reduction in UV254 increased with an increasing dose of oxidant and UV irradiation. The reduction in UV254 for UV/Cl2, UV/ClO2 and UV/H2O2 was 59.5%, 26.5%, and 17.5% respectively, for 0.71 mM equimolar concentration of oxidant and 1920 mJ/cm2 UV irradiation, as evident from a pseudo-first order kinetics study. Similarly, degradation of the high molecular weight to low molecular weight (LMW) fraction was pronounced for UV/Cl2. The coagulation efficiency decreased after UV-induced AOP in the following order: UV/H2O2 > UV/ClO2 > UV/Cl2. By contrast, the low-energy FPF process showed a higher removal of LMW fractions than CGS. Thus, low-energy FPF could be an alternative technology for the UV-induced AOP treatment system.

Physical and Biological Treatment Technologies of Slaughterhouse Wastewater: A Review

Physical and biological treatment technology are considered a highly feasible and economic way to treat slaughterhouse wastewater. To achieve the desired effluent quality for disposal or reuse, various technological options were reviewed. However, most practical operations are accompanied by several advantages and disadvantages. Nevertheless, due to the presence of biodegradable organic matter in slaughterhouse waste, anaerobic digestion technology is commonly applied for economic gain. In this paper, the common technologies used for slaughterhouse wastewater treatment and their suitability were reviewed. The advantages and disadvantages of the different processes were evaluated. Physical treatments (dissolved air floatation (DAF), coagulation–flocculation and sedimentation, electrocoagulation process and membrane technology) were found to be more effective but required a large space to operate and intensive capital investment. However, some biological treatments such as anaerobic, facultative lagoons, activated sludge process and trickling filters were also effective but required longer start-up periods. This review further explores the various strategies being used in the treatment of other wastewater for the production of valuable by-products through anaerobic digestion.

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.

Pre-oxidation enhanced cyanobacteria removal in drinking water treatment: A review

Cyanobacterial bloom has many adverse effects on source water quality and drinking water production. The traditional water treatment process can hardly achieve satisfactory removal of algae cells. This review examines the impact of pre-oxidation on the removal of cyanobacteria by solid-liquid separation processes. It was reported that the introduction of chemical oxidants such as chlorine, potassium permanganate, and ozone in algae-laden water pretreatment could improve algae removal by the subsequent solid-liquid separation processes. However, over dosed oxidants can result in more serious water quality risks due to significant algae cell lysis and undesirable intracellular organic matter release. It was suggested that moderate pre-oxidation may enhance the removal of cyanobacteria without damaging algae cells. In this article, effects of moderate pretreatment on the solid-liquid separation processes (sedimentation, dissolved air flotation, and membrane filtration) are reviewed.

Structure and indicators of electric energy consumption in dairy wastewater treatment plant

The aim of the research was to determine the indicators of electricity consumption in every stage of the dairy sewage treatment process in relation to the sewage flow and the load of removed organics (BOD5, COD) and nutrients (TN, TP). The research was conducted in a dairy wastewater treatment plant (WWTP) consisting of mechanical treatment, averaging tank, dissolved air flotation (DAF) and biological treatment with sequence batch reactors (SBRs). Energy consumption was measured with the help of transducers. Indicators of unit electricity consumption were determined on the basis of 95 measurement series of energy consumption, sewage flow and removed load. The mean value of total unit energy consumption relating to the flow for the entire WWTP was 2.29 kWh·m−3, while for biological treatment 1.17 kWh·m−3 and 0.05 kWh·m−3 for DAF. The mean values of indicators relating to removed pollutants load for the entire WWTP were: 1.89 kWh·kgrem BOD5−1, 1.30 kWh·kgrem COD−1, 48.61 kWh·kgrem TN−1 and 160.01 kWh·kgrem TP−1. During biological treatment, energy consumption indicators were on average: 1.65 kWh·kgrem BOD5−1 and 1.19 kWh·kgrem COD−1, 52.90 kWh·kgrem TN−1 and 141.26 kWh·kgrem TP−1, while for DAF: 0.12 kWh·kgrem BOD5−1, 0.09 kWh·kgrem COD -1, 3.85 kWh·kgrem TN−1 and 16.17 kWh·kgrem TP−1. It was found that the biological treatment in SBRs was responsible for 54.1% of the total energy consumption of dairy WWTP. Aerobic sewage sludge treatment accounted for 17.0% of total consumption, mechanical treatment 17.1%, deodorization 2.6%, and other (social, lighting etc.) 6.9%, while DAF only 2.3%. The real-time electricity metering system enabled the optimisation of the electricity consumption in the WWTP, taking into account its consumption in unit processes and the removed pollutants load. The application of this system enabled to make corrections that reduced energy consumption while maintaining the required treatment efficiency.

Assessing Pretreatment Effectiveness for Particulate, Organic and Biological Fouling in a Full-Scale SWRO Desalination Plant.

In this study, the removal of particulate, organic and biological fouling potential was investigated in the two-stage dual media filtration (DMF) pretreatment of a full-scale seawater reverse osmosis (SWRO) desalination plant. Moreover, the removal of fouling potential in two-stage DMF (DMF pretreatment) was compared with the removal in two-stage DMF installed after dissolved air floatation (DAF) (DAF-DMF pretreatment). For this purpose, the silt density index (SDI), modified fouling index (MFI), bacterial growth potential (BGP), organic fractions and microbial adenosine triphosphate (ATP) were monitored in the pretreatment processes of two full-scale SWRO plants. Particulate fouling potential was well controlled through the two stages of DMF with significant removal of SDI15 (>80%), MFI0.45 (94%) and microbial ATP (>95%). However, lower removal of biological/organic fouling potential (24–41%) was observed due to frequent chlorination (weekly) of the pretreatment, resulting in low biological activity in the DMFs. Therefore, neutralizing chlorine before media filtration is advised, rather than after, as is the current practice in many full-scale SWRO plants. Comparing overall removal in the DAF-DMF pretreatment to that of the DMF pretreatment showed that DAF improved the removal of biological/organic fouling potential, in which the removal of BGP and biopolymers increased by 40% and 16%, respectively. Overall, monitoring ATP and BGP during the pretreatment processes, particularly in DMF, would be beneficial to enhance biological degradation and lower biofouling potential in SWRO feed water.

Empirical evaluation for design parameters and operating characteristics of the integrated sedimentation and dissolved air flotation (SeDAF) process at the pilot-scale plant

Empirical evaluation for design parameters and operating characteristics of the integrated sedimentation and dissolved air flotation (SeDAF) process at the pilot-scale plant