Dissolved Air Flotation Research Articles

Full-scale performance and microbial community evolution using dopamine modified ceramic membrane submerged membrane biological reactor in treating young landfill leachate

In this project, ceramic membrane submerged membrane biological reactor (SMBR) was integrated to dissolved air flotation (DAF)-up-flow anaerobic sludge blanket (UASB)-anoxic and aerobic (A/O) system in treating young landfill leachate with a capacity of 300 m3 /day over 185 days’ operation. High removal efficiencies of chemical oxygen demand (COD) (96.8 %), ammonia nitrogen (83.4 %) and total nitrogen (79.6 %) were achieved via DAF-UASB -A/O system. The membrane permeate COD was below 356 mg/L. The permeate turbidity was stable below 11 NTU, met the condition for further ultrafiltration treatment. The SMBR system was operated stability at the flux of 26 LMH because of excellent surface hydrophilicity of the dopamine modified ceramic membrane. Remarkably, immersed chemical cleaning can recover the filterability entirely, indicating the dopamine modified ceramic membrane SMBR can be recognized as fouling–free MBRs. The foulants removal after chemical cleaning on the ceramic membrane was detailly analyzed by scanning electron microscopy coupled with energy dispersive X-ray. The comparative microbial analysis between sludge Day-1 and Day-185 revealed that significant changes of microbial community occurred. Regarding the nitrifying and denitrifying bacteria, Thauera was identified as potential functional specie in simultaneous methanogensis and denitrification process in the UASB reactor. High populations of Proteobacteria, Planctomycetes, Bacteroidetes and Chloroflexi contributed the nitrification and denitrification in the A/O system. The anaerobic ammonia oxidation process might happen due to the identified Planctomycetes. At the genus level, genera, such as Thauera, Phycisphaerae and Betaproteobacteria, with high abundances were functional species ensuring the nitrogen removal in the A/O environment.

Optimization of Dissolved Air Flotation (DAF) process for the treatment of oily water from biodiesel production

Biodiesel production has become one of the most efficient ways of diversifying the energy matrix. However, the increase in biodiesel production increases the generation of wastewater. Therefore, this study aimed to characterize the wastewater generated in the biodiesel washing process, obtained by the alkaline transesterification of sunflower oil, and to evaluate its treatment by the dissolved air flotation (DAF) system, using a Central Composite Rotational Design (CCRD). The first DCCR was carried out with 4 independent variables: pH, Coagulant Dose (CD), Polymer Dose (PD), and Recirculation Rate (RR), with the response variables being apparent color removal and turbidity removal. Based on the results of the first DCCR, optimization tests were designed with DC and DP as independent variables and apparent color, turbidity, COD, and oil and grease (OG) as response variables. The process showed high apparent color and turbidity removal efficiency. The best results were obtained in tests 10 (DC = 1545 mg.L-1 and DP = 1050 mg.L-1) and 3 (DC = 700 mg.L-1 and DP = 8.8 mg.L-1), with the removal of 99.88% and 99.22%, respectively. For the COD and OG parameters, the best results were observed in tests 8 (DC= 555 mg.L-1 and DP= 6 mg.L-1) and 5 (DC= 1050 mg.L-1 and DP= 6 mg.L-1), with 98% and 99.42% removal, respectively. FAD treatment using the combination of coagulant and cationic polymer proved to be highly efficient in treating wastewater from biodiesel production.

Removal of Microplastic From Liquid Medium By Dissolved Air Flotation

Removal of Microplastic From Liquid Medium By Dissolved Air Flotation

Effects of coagulation/flocculation followed by dissolved air flotation on anaerobic digestion of coffee processing wastewater

Effects of coagulation/flocculation followed by dissolved air flotation on anaerobic digestion of coffee processing wastewater

Performance evaluation of a wastewater treatment plant from a dairy in the state of Minas Gerais, Brazil: a case study.

Wastewater generated in dairies has a strong polluting potential and must be treated for disposal into water bodies or reuse. The objective of this work was to analyze the efficiency of removing pollutants through the processes used by a wastewater treatment plant (WWTP) of a dairy located in the state of Minas Gerais, Brazil. For this purpose, the results of the characterization analyses referring to raw and treated wastewater were interpreted. The results showed that the sequence of processes used in the WWTP (water/oil separation, dissolved air flotation, followed by biodegradation in an upflow anaerobic filter) is efficient in removing on average 99.1% of COD and 98.7% of BOD5. For treated wastewater, data on pH and concentration of total suspended solids, total ammoniacal nitrogen, surfactants, settleable solids, and oils and greases also met the standards for disposal into water bodies. For reuse in agriculture, treated wastewater can be used for irrigation, but it is recommended to additionally evaluate the Escherichia coli parameter. When evaluating the existence of linear correlation between COD and BOD5 data, it was possible to find only a moderate correlation (R2 equal to 0.7) for treated wastewater.

Laboratory validation of the automated diagnosis of intestinal parasites via fecal sample processing for the recovery of intestinal parasites through the dissolved air flotation technique

BackgroundTechniques for diagnosing intestinal parasites need technological advancements in the preanalytical (collection/processing) and analytical (detection) stages. The dissolved air flotation (DAF) technique effectively recovers parasites from processed feces for routine diagnosis. Artificial intelligence (AI) is a practical and affordable alternative to modernize the analysis stage of microscopy images and generates high efficiency in the parasitological examination of feces.MethodsThe objective of this study was to standardize a laboratory protocol for stool processing using the DAF technique in conjunction with an automated diagnosis of intestinal parasites (DAPI) system. A total of 400 samples were obtained to perform the tests with the use of DAF to verify the recovery of the parasites as a function of the chemical reagent (polymer and surfactant), the volume of the flotation tube, and standardization of smear assembly on a microscopy slide, with automated analysis by DAPI. The DAF protocol that obtained the most satisfactory results in terms of parasite recovery (P < 0.05) and slide positivity was compared with the Three Fecal Test (TF-Test) protocol with manual (microscopists) and automated (DAPI) evaluation. We compared the sensitivity with the modified TF-Test technical protocol and the diagnostic agreement with the gold standard (Kappa) result.ResultsThere was no significant difference in the parasite recovery between the 10 ml and 50 ml tubes (P > 0.05). The surfactants showed a range of parasite recoveries between 41.9% and 91.2% in the float supernatant. We obtained a maximum positivity of 73% of the assembled slides when we applied DAF processing with 7% CTAB surfactant and 57% positivity with the modified TF-Test technique. Regarding diagnostic performance, the TF-Test-modified and DAF techniques used in fecal processing for subsequent computerized analysis by AI presented sensitivities of 86% and 94%, with kappa agreements of 0.62 and 0.80 (substantial), respectively.ConclusionsThe DAF protocol defined in this study and the DAPI system are innovative processes for parasite recovery and fecal debris elimination that are favorable for effectively detecting pathogenic structures in laboratory diagnosis.Graphical

Comparative life cycle assessment (LCA) of pre-treatment technologies for desalination in South Africa

In the context of South Africa’s water scarcity, desalination has emerged as a possible solution for coastal areas. However, the quality of the intake water for desalination is often problematic, prompting the need for pre-treatment. The aim of this study was to conduct a comparative environmental life cycle assessment (LCA) on 4 seawater filtration systems intended for the pre-treatment of a reverse osmosis desalination project. These systems were implemented in a pilot trial and are based on modern water treatment technologies, namely, granular filtration (pressure driven and gravity driven), dissolved air flotation (DAF), and ultrafiltration (UF). For all 4 systems, data were collected for both the construction and operation phases, and LCAs were performed, resulting in environmental scores that allow for comparison based on the pre-treatment of 1 kL of seawater of the same quality. The SimaPro LCA tool and the ReCiPe midpoint method were used and environmental scores were calculated for 18 impact categories, including climate change, acidification, toxicity, eutrophication, resource depletion, etc. This methodology also allowed the identification of the highest environmental burdens/scores within each system. The most significant finding is that local electricity consumption is responsible for the greatest proportion of environmental impacts. Thus, the systems consuming more energy for operating equipment such as blowers, pumps, and mixers were found to have the highest environmental burdens. Hence, the DAF system has the highest environmental scores for most impacts, followed by the single-phase gravity filtration system, then the two-phase partial pressure filtration system and finally the UF system. Therefore, focus should shift towards energy optimisation of process units, especially the rotary ones, as well as energy mitigation and recovery strategies. The use of renewable energy for pre-treatment should also be considered locally.

Comparative study on wastewater pollution reduction: dissolved air flotation versus acidic flotation and pH effects

Comparative study on wastewater pollution reduction: dissolved air flotation versus acidic flotation and pH effects

Projektowanie zakładu uzdatniania wody przy wsparciu modeli laboratoryjnych

The subject of the research focused on the possibilities of supporting the design of surface water treatment plants using laboratory models. Within the pilot study, the possibilities of using different water treatment processes in the treatment of water from the water reservoir Nové Mlýny in the Czech Republic were assessed. The planned treatment plant is to supply a future recreational site from a shallow reservoir with significant eutrophication and chemical industry in the drainage basin. Coagulation, sedimentation, dissolved air flotation, membrane filtration processes and adsorption on granular activated carbon were investigated. These processes were identified by the preliminary study as applicable to water treatment and it was necessary to determine which could be applied given the site conditions. Laboratory models for the individual processes were used during the laboratory testing. During the research, problems encountered were debugged and the models were modified and some extensions were added to the original models. The coagulation and sedimentation processes were investigated using conventional jar tests. The dissolved air flotation process was simulated using a modified jar test and a lab scale model. Different types and doses of coagulants, mixing parameters and residence times were investigated in the tests. Turbidity value was used as an optimization parameter due to its rapidity of determination and low cost. For some tests, potassium permanganate oxidizability (also known as the permanganate index) was also used as an evaluation parameter so that different evaluation parameters could be compared. In addition, for the dissolved air flotation process, the parameters of the produced sludge - its quantity, suspended solids content and chemical oxygen demand - were monitored. These parameters are crucial for discharge of waste water into the sewer and its costs. The adsorption tests on granular activated carbon were performed as batch tests. The evaluation parameter was the manganese index. Another possible variant of activated carbon tests is a continuous flow-through column. These columns also allow monitoring of the process of fouling and the evolution of the effluent over time. The pilot project then used the results of the laboratory tests to create a design for a treatment plant in the area of interest and selected parts of the project documentation. The pilot project demonstrated the usefulness of laboratory testing as a tool to support the design of drinking water treatment plants. At the same time, these tests allow for a faster and more certain identification of the appropriate water treatment technology and thus reduce the extent of semi-operational testing at the site, leading to a more efficient use of funds by investors.

Numerical investigation on mixing behaviour in the contact zone of an industrial‐scale dissolved air flotation tank

AbstractThe mixing behaviour of the wastewater and the recycle bubbly water in the contact zone could affect the separation performance of dissolved air flotation systems. In this study, the mixing characteristics in the contact zone of an industrial‐scale dissolved air flotation tank were investigated using the computational fluid dynamics method. At first, the influence of the turbulence model on the simulation results was clarified. It is demonstrated that the realizable k‐ε model could predict the gas holdup distribution with better accuracy, and the maximum relative deviation between the predicted gas holdup and the experimental results is only 10%. The influence of the geometry and operating parameters on the mixing process was then studied numerically. It is found that the mixing performance in the contact zone could be improved by decreasing the height position of the nozzle inlet in a certain range. The reason is that microbubbles disperse better in the bottom region and a double circulation flow state forms in the contact zone when the nozzle inlet is installed at a low height. Additionally, the mixing process could be further enhanced by decreasing the diameter of the nozzle inlet. As to the operating conditions, increasing the recycle ratio could not only increase the gas holdup but also improve the mixing performance in the contact zone. When the recycle flow rate remains constant, increasing the wastewater flow rate will lead to a decrease in gas holdup and deterioration of the mixing effect.

A digital image analysis approach to understand the microscopic and macroscopic phenomena in dissolved air flotation

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

Techno-economic comparison of flocculation combined with dissolved air flotation versus sedimentation for microalgae harvesting

Microalgae are a promising new source of biomass but the harvesting method needs to optimised to reduce the production cost. In a two-step harvesting process, the bulk water is removed via flocculation (first step) followed by complete dewatering using centrifugation (second step). Flocs can be separated from the bulk water using either gravity sedimentation or dissolved air flotation (DAF). DAF requires a more complex setup and demands more energy than sedimentation, but it is faster and generates a sludge with a higher dry matter content. This study aims to compare the performance of DAF and sedimentation in laboratory experiments and then estimates the cost for a 100-hectare farm using sedimentation versus DAF for harvesting (step-1) and using a decanter centrifuge (step-2) for dewatering. Chlorella vulgaris was the model species and poly(dimethylaminoethyl methacrylate) (pDMAEMA) was synthesised and used as the flocculant. In bench-scale testing, sedimentation and DAF achieved maximum harvesting efficiencies of 87 % and 98 %, respectively. Sedimentation was slow and generated a sludge with low solids content (1.1 %). DAF achieved a fast separation and generated a sludge with 3× higher solids content of 3.4 %. When estimating the costs of biomass harvesting at 100-hectare scale, DAF was found to have higher capital and operating expenditure than sedimentation. However, when combining harvesting with the dewatering step in a two-stage harvesting-dewatering system, the total capital and operating expenditure was projected to be 20–38 % and 10–18 % cheaper, respectively, than sedimentation. This is due to the faster separation, higher sludge solids content, and greater separation efficiencies obtained via DAF than sedimentation. Hence, DAF is recommended over sedimentation for harvesting microalgae. Importantly, this study showcases that contrary to conventional belief, flocculation–DAF is cheaper than flocculation–sedimentation for large-scale algal harvesting.

Comparison of dissolved air flotation and sedimentation for the treatment of two waters with low turbidity in Colombia

Comparison of dissolved air flotation and sedimentation for the treatment of two waters with low turbidity in Colombia

The Biophysical Properties of Microalgal Cell Surfaces Govern Their Interactions with an Amphiphilic Chitosan Derivative Used for Flocculation and Flotation.

Microalgae show great promise for producing valuable molecules like biofuels, but their large-scale production faces challenges, with harvesting being particularly expensive due to their low concentration in water, necessitating extensive treatment. While methods such as centrifugation and filtration have been proposed, their efficiency and cost-effectiveness are limited. Flotation, involving air-bubbles lifting microalgae to the surface, offers a viable alternative, yet the repulsive interaction between bubbles and cells can hinder its effectiveness. Previous research from our group proposed using an amphiphilic chitosan derivative, polyoctyl chitosan (PO-chitosan), to functionalize bubbles used in dissolved air flotation (DAF). Molecular-scale studies performed using atomic force microscopy (AFM) revealed that PO-chitosan's efficiency correlates with cell surface properties, particularly hydrophobic ones, raising the question of whether this molecule can in fact be used more generally to harvest different microalgae. Evaluating this, we used a different strain of Chlorella vulgaris and first characterized its surface properties using AFM. Results showed that cells were hydrophilic but could still interact with PO-chitosan on bubble surfaces through a different mechanism based on specific interactions. Although force levels were low, flotation resulted in 84% separation, which could be explained by the presence of AOM (algal organic matter) that also interacts with functionalized bubbles, enhancing the overall separation. Finally, flocculation was also shown to be efficient and pH-independent, demonstrating the potential of PO-chitosan for harvesting microalgae with different cell surface properties and thus for further sustainable large-scale applications.

Effective Removal of Ibuprofen from Aqueous Solution Using Cationic Surface-Active Agents in Dissolved Air-Flotation Process

This research paper focuses on the removal of the nonsteroidal anti-inflammatory drug, ibuprofen, from an aqueous solution using a dissolved air flotation process. The comparison of different types of cationic surface-active agents such as cetyltrimethyl ammonium bromide (CTAB), tetrabutyl ammonium bromide (TBAB), and octyltrimethyl ammonium bromide (OTAB) have been employed to scrutinize the effective removal of the ecotoxic pharmaceutically active compound. The work included the influencing parameters such as pressure, contact time, surfactant dosage, pH, flow rate, and initial concentration owing to the best-optimized conditions. The maximum removal rate of 96.09% was achieved at 15 min for CTAB, TBAB had 62.36% at 45 min, and 89.6% was obtained for OTAB at 30 min, with 50 mg L−1 as the initial concentration and pH = 4. The removal rate was better with the optimized dosage of CTAB at 0.6 g, TBAB at 1.2 g, and OTAB at 1.0 g. It was observed that the geometric shape of the surface-active agents had greater impacts on the contaminants’ efficiency. CTAB and OTAB were combined to find out the best possible removal rate of contaminants. The synergistic effect augments surfactant-based occurrence to be better in forming a good foaming effect and tends to have a lower critical micelle concentration (CMC). From the evaluation of kinetic models, pseudo-second-order flotation kinetics fitted the experimental data best. Furthermore, the formed metabolites that had been identified using gas chromatography-mass spectrometry were found to be less toxic than the parenting compounds.

Modelling and application of dissolved air flotation for efficient separation of microplastics from sludges and sediments

The pervasive presence of microplastics in our environment necessitates urgent measures to prevent further release and address existing contamination hotspots. This work focuses on the removal of microplastics from sludges and sediments through the application of dissolved air flotation (DAF). In addition to experimental investigations, the study presents the development of a predictive model for the formation of aggregates comprising air bubbles and microplastics in the DAF contact zone. First an empirical model was established to predict the attachment efficiency between air bubbles and particles (αdb). To this end, the experimental attachment efficiency was determined for various plastics, with varying particle sizes and shape factors, and system conditions. The obtained data set was utilized to establish an empirical model by PLS regression describing αdb based on particle size, bubble size, density, Hamaker constant, contact angle, solid load, aspect ratio, circularity, and sphericity, resulting in an MSPE of 0.011 and adjusted-R² of 0.64. Secondly, a semi-deterministic model based on the XDLVO theory was developed using MLR, where αdb was described by the natural logarithm of the Van der Waals, electrostatic and hydrophobic forces acting between the particle and air bubble, and the solid load, with an RSE of 0.067 and adjusted-R² of 0.63. Finally, the applicability of these models was demonstrated in a case study on industrial sludge consisting of sediment and PVC microplastics. Validation of the attachment efficiency and the dimensioning of a DAF unit for processing this sludge at a capacity of 20 m³.h−1 emphasize the practical implications of the developed models.

Cultivation of Microalgae (Scenedesmus sp.) Using Coal Mining Wastewater and Separation via Coagulation/Flocculation and Dissolved Air Flotation (DAF)

Algae growth can be carried out in treated mine waters, providing biomass and helping to achieve the standards for water discharge. However, efficient separation of algae from the aqueous medium is crucial. The present work investigated the stability of Scenedesmus sp. in treated acid drainage from coal mining and assessed the harvesting of microalgae via coagulation/flocculation and dissolved air flotation (DAF). Successful algae growth was achieved, with cells remaining suspended in the water at a wide range of pH values, requiring the use of reagents for destabilization/aggregation. Algae coagulation/flocculation was attained with the use of tannin or ferric chloride associated with an anionic polymer flocculant at a pH of 8.0 ± 0.1. When combined with the flocculant, both tannin and the inorganic coagulant proved effective in enhancing floc stability and hydrophobicity for the DAF process. In summary, this operational approach facilitated algae biomass recovery and significantly reduced turbidity in the treated water. Finally, a schematic diagram illustrating the algae cultivation and harvesting process is presented, offering a practical alternative to acid mine drainage (AMD) treatment refinement associated with algae biomass production.

Optimizing electrocoagulation for poultry slaughterhouse wastewater treatment: a fuzzy axiomatic design approach

White meat consumption is increasing day by day, and accordingly, there is an increase in the amount of wastewater resulting from the processes. Today, the reuse of wastewater has become a goal within the scope of the Green Deal. For this reason, wastewater treatment with high pollution and volume has gained importance. In this study, the fuzzy axiomatic design (FAD) method, one of the multi-criteria decision-making methods, has been used. With this method, coagulation, electrocoagulation (EC), dissolved air flotation (DAF), and anaerobic treatment alternatives preferred in poultry slaughterhouse wastewater (PSW) treatment were compared with each other and their information contents were calculated. The information content from the smallest to the largest is EC, DAF, coagulation, and anaerobic treatment, respectively. This treatment method was chosen because the smallest information content is in electrocoagulation. EC was applied to bloody PSW containing 1% blood by volume. The effectiveness of Fe and Al electrodes for PSW treatment in the batch EC reactor has been compared. The effective surface areas of 2 anodes and 2 cathodes connected bipolarly in the processes are 288 cm2. The electrolyte, pH, time, and current density effects on energy consumption were also investigated. The optimum conditions for Al and Fe electrodes were found to be 0.5 g·L−1 NaCl concentration, pH 5, 0.639 mA·cm−2 current density, and 5 min time. Under optimum conditions for the Fe electrode, COD, TOC, TN, and oil-grease removal efficiencies were determined as 76.3%, 71.8%, 70%, and 74%, respectively. Moreover, the highest COD, TOC, TN, and oil-grease removal efficiencies were achieved with an Al electrode (82.2%, 82.3%, 82.7%, and 78.9%, respectively). The experimental data were fit to a variety of isotherms and kinetic models to determine the characteristics of the EC. The results indicated that the pseudo-second-order equation provided the best fit for COD removal. Under optimum conditions, the operating cost was calculated as $3.39 and $3.09 for Al and Fe electrodes, respectively. In this study, the fuzzy axiomatic design method was used for the first time to select the most appropriate treatment method for PSW. In addition, blood, a major problem for the poultry slaughterhouse industry, was mixed with PSW at a ratio of 1% (v/v) and treated with EC for the first time with high removal efficiency. By treating PSW, which has a high pollution load, with electrocoagulation, the pollution load of the water to be given to secondary treatment has been greatly reduced.

Combining Dissolved Air Flotation (DAF) and Modified Moving Bed Biofilm Reactors (MMBBR) for Synthetic Oily Wastewater Treatment

&lt;p&gt;Numerous industrial processes, including petroleum refining, food production, car washes, leather manufacturing, and slaughter houses, generate significant volumes of wastewater due to their substantial water consumption during processing. The presence of oily wastewater has detrimental effects on surface and ground water resources, Human health and aquatic ecosystems. This study aims to integrate dissolved air flotation (DAF) and moving bed biofilm reactors (MBBR) for the treatment of oily wastewater. For this reason, a synthetic oily wastewater was prepared by utilizing commercially available powdered starch as an organic source, along with diesel oil and a finely ground soil. In addition, the experiments were designed and analyzed using Response Surface Methodology (RSM). DAF reactor factors were flotation time and air flow rate. While the MBBR reactor variables were mixing time and hydraulic retention time (HRT). The responses were chemical oxygen demand (COD), oil and grease(O&amp;amp;G), ammonia (NH3-N) and total suspended solids (TSS). Optimum results obtained by RSM for the DAF were 10 min for the flotation time and air flow rate of 72 L/min. in addition, HRT for both MBBRs was 23.5 hr and mixing time of 13 min and 23 min for MBBR1 and MBBR2 respectively.&lt;/p&gt;

Removal of chromium using rhamnolipid biosurfactant, ferrous sulfate and cationic tannin‐based flocculant in a dissolved air floating system using a central composite design (CCD)

AbstractThis research studied the wastewater chromium removal efficiency by dissolved air flotation (DAF) using a rhamnolipid (RL) biosurfactant as a collector. An experimental flotation DAF apparatus with 6 vessels of 2 L containing a coupled saturator injecting compressed air at 5.88 kPa in the vessels was used. The total RL concentration of the broth resulting from fermentation was 9 ± 1.0 g/L. This broth was used in nature in the DAF experiments. A central composite design (CCD) was used to optimize removal of Cr(VI) and total Cr with regards to two independent variables, pH (3.17–8.83) and iron concentration of the medium (0–225.0 mg/L), with a three assays performed at the conditions of the central point of the design. The experimental conditions for DAF were an initial hexavalent Cr concentration of 100 mg/L; RL broth volume of 500 mL; saturated with oxygen water volume of 200 mL; and a rapid mixing time of 6 min through stirring at 120 rpm. The results showed that under acidic pH conditions and with high iron concentrations, both the Cr(VI) and total Cr removal rates were highest. The optimal removal region determination was at a pH of 3.5 and iron concentration of 180 mg/L. Subsequently, cationic tannin‐based flocculant was also evaluated as a collector, and ferrous sulfate was used as a coagulant during Cr(III) removal. The best Cr(III) removal percentage was obtained at cationic polymer concentrations of 300 mg/L with Cr(III) removal of 50.8% and a pH of 5.5.