Dissolved Air Flotation Treatment Research Articles

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.

Kinetic, artificial neural network, and statistical modeling to optimize the parameters of the air flotation process to remove latex suspended solids in ABS wastewater

As China's contemporary industrial production undergoes continuous enhancement and economic development, there is a remarkable surge in the consumption of acrylonitrile–butadiene–styrene (ABS) materials. The extensive application of dissolved air flotation (DAF) has been adopted to effectively eliminate a substantial quantity of suspended solids present in ABS wastewater. Attaining precise control over the DAF process stands as the pivotal factor in enhancing the removal efficiency. In this study, we had constructed an air flotation apparatus and developed an open-structure software within the master computer. We innovatively compared the response surface methodology (RSM), artificial neural network (ANN), and adsorption kinetic model (AKM) with ABS wastewater DAF treatment process by incorporating relevant parameters. The results demonstrated that the ANN exhibited superior fitting capability in comparison to both the RSM and AKM. Drawing from the comparative results, it was evident that, in the context of COD removal, the ANN surpassed the RSM by margins of 5.06 %, 80 %, and 4.44 % in terms of R-squared (R2), Average Absolute Relative Error (AARE), and Root Mean Square Error (RMSE), respectively. The ANN outperformed the AKM by percentages of 35.71 %, 95.65 %, and 74.66 % concerning R2, AARE, and RMSE, respectively. Similar conclusions were drawn for suspended solids (SS) removal. This study provided valuable support for the adaptive adjustment of successive reaction conditions and the prediction of outlet quality, thus possessing commendable applicative significance and practical utility.

Treatment of fish processing plant wastewater using dissolved air flotation and pilot-scale biochar column filtration

Wastewaters from fish processing cause a high organic load for municipal wastewater treatment and can interfere with treatment operations due to their high oil and grease content. In the present study, a modular dissolved air flotation (DAF) unit was used to remove oil, grease and other suspended solids from fish processing plant wastewater. After DAF treatment, the residual particles and nutrients were adsorbed onto a mixture of hemp and spruce biochar in a pilot-scale column filtration system. The proposed integrated treatment process aims to improve the quality of the fish processing wastewater, facilitate water reuse, and recover the dissolved nutrients in a reusable form. The DAF treatment removed nearly all the oil and grease from the wastewater. Also, chemical oxygen demand, turbidity and phosphorus concentration clearly decreased during the DAF process. The biochar filtration further clarified the DAF-treated wastewater and partly adsorbed the residual nutrients. Furthermore, in the spent biochar mixture, the nitrogen and phosphorus content increased significantly (N to 9.1–10.5 mg/g, P to 0.32–1.38 mg/g), which indicates the improved properties of the biochar as a possible soil conditioner.

Improving Nickel Recovery in Froth Flotation by Purifying Concentrators Process Water Using Dissolved Air Flotation

The pressure for saving water by closing the water loops in mineral processing is increasing continuously. The drivers for higher recirculating rates include water scarcity in dry areas, environmental legislation that is becoming stricter in most countries, limitations set for wet tailings management and the increased demands for social licenses to operate. At the same time, to make mineral processing sustainable, the recovery of valuable minerals should be maximized. This leads for a need to close the process water circulation. To see the effect of closed water circulation on metallurgical performance, flotation tests were carried out with nickel concentrate thickener overflow water before and after the process of water purification by dissolved air flotation (DAF). Both total nickel recovery and concentrate grade in laboratory scale flotation tests to the Ni rougher-scavenger concentrate increased after DAF treatment. Chemical and mineralogical characterizations revealed that after DAF treatment, the process water contained fewer metal hydroxides and less fine-grained silicate mineral particles, which is most likely the reason for the improvement in the nickel flotation performance. Based on the feasibility study, improved nickel recovery by DAF treatment of process water can bring economic benefits at a concentrator plant.

Electrocoagulation-electroflotation for primary treatment of animal rendering wastewater to enable recovery of fats

Rendering wastewater (RW) contains high levels of fats from the rendering process that recovers fats and proteins from waste animal fatty tissue. Primary treatment to remove floatable fats is necessary to avoid issues for downstream RW treatment. Recovery of waste fats that can be sent back to the rendering process can be an additional gain from RW primary treatment. Dissolved air flotation (DAF) with the addition of polymer coagulants is commonly used for primary treatment of RW, but this has two disadvantages: polymer coagulants are undesirable contaminants in reused fats and the fat quality is degraded through oxidation by pressurized air during DAF treatment. In this work, RW was treated by electrocoagulation-electroflotation (EC-EF) in a novel horizontally-placed electrode pair design as an alternative to DAF. EC-EF performed better in COD removal with increasing current densities. In situ flotation within the electrochemical cell from hydrogen gas bubbles produced was able to concentrate and preserve long chain fatty acids (LCFA). Treatment at higher current densities within the electrochemical cell generated surplus coagulants and allowed further coagulation in a separate following step. Longer mixing duration in the post-EC-EF treatment step enhanced overall COD removal. The overall COD removal for EC-EF with applied current densities of 2 mA/cm2 reached 69.5 ± 4.8% after 15 min of mixing at 100 rpm followed by 15 min of sedimentation. EC-EF thus provides competitive treatment performance and recovery of well-preserved rendering products.

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

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

Simulating behavior of petroleum compounds during refinery effluent treatment using the SimpleTreat model

Distribution and elimination of petroleum products can be predicted in aerobic wastewater treatment plants (WWTPs) using models such as multimedia fate model SimpleTreat. An advantage of the SimpleTreat model is that it only requires a few basic properties of a chemical in wastewater to calculate partitioning, biodegradation and ultimately emissions to air, surface water and produced sludge. The SimpleTreat model structure reflects a WWTP scheme. However, refinery WWTPs typically incorporate more advanced treatment processes such as dissolved air flotation (DAF), a process that clarifies wastewaters by the removal of suspended matter such as oil or solids. The objective of this work was to develop a WWTP removal model that includes DAF treatment. To understand how including a DAF in the model affects the predicted concentrations of petroleum constituents in effluent, we replaced the primary sedimentation module in SimpleTreat with a module simulating DAF. Subsequently, we compared results from the WWTP-DAF model with results obtained with the original SimpleTreat model for a library of over 1500 representative hydrocarbon constituents. The increased air-water exchange in a WWTP-DAF unit resulted in higher predicted removal of volatile constituents. Predicted removal with DAF was on average 17% larger than removal with primary sedimentation. We compared modelled results with measured removal data from the literature, which supported that this model refinement continues to improve the technical basis of assessment of petroleum products.

Dissolved air flotation as a potential treatment process to remove Giardia cysts from anaerobically treated sewage

ABSTRACTControlling Giardia cysts in sewage is an essential barrier for public health protection, reducing possible routes of protozoa transmission. The aim of this study was to evaluate the capability of dissolved air flotation (DAF), on a bench scale, to remove Giardia cysts from anaerobic effluent. Moreover, removals of indicator microorganisms and physical variables were also investigated. Flocculation conditions were studied, associating different flocculation times with different mean velocity gradients. DAF treatment achieved mean log removals in the range of 2.52–2.62 for Giardia cysts, depending on the flocculation condition. No statistical differences were observed among the flocculation conditions in terms of cyst removal. Low levels of turbidity and apparent color obtained from the treated effluent may indicate good treatment conditions for the DAF process in cyst removal. Indicator microorganisms were not able to predict the parasitological quality of the wastewater treated by flotation in terms of cyst concentrations. The DAF process provided an effective barrier to control cysts from sewage, which is an important parasite source.

Effect of adsorbent addition on floc formation and clarification

Adding adsorbent into the coagulation process is an emerging treatment solution for targeting hard-to-remove dissolved organic compounds from both drinking water and industrial wastewater. The impact of adding powdered activated carbon (PAC) or organoclay (OC) adsorbents with ferric chloride (FeCl3) coagulant was investigated in terms of potential changes to the coagulated flocs formed with respect to size, structure, and breakage and regrowth properties. The ability of dissolved air flotation (DAF) and sedimentation (SED) clarification processes to remove hybrid adsorbent-coagulant flocs was also evaluated through clarified water quality analysis of samples collected in bench-scale jar test experiments. The jar tests were conducted using both a synthetic fresh water and oily wastewater test water spiked with dissolved aromatic compounds phenol and naphthalene. Results of the study demonstrated that addition of adsorbent reduced the median coagulated floc size by up to 50% but did not affect floc strength or regrowth potential after application of high shear. Experimental results in fresh water demonstrated that sedimentation was more effective than DAF for clarification of both FeCl3-PAC and FeCl3-OC floc aggregates. However, experimental tests performed on the synthetic oily wastewater showed that coagulant-adsorbent floc aggregates were effectively removed with both DAF and sedimentation treatment, with lower residual turbidity achieved in clarified water samples than with coagulation treatment alone. Addition of OC or PAC into the coagulation process resulted in removals of over half, or nearly all of the dissolved aromatics, respectively.

Intensification Dissolved Air Flotation Treatment of Oil-Containing Wastewater

The paper is devoted to the oil-containing water treatment by dissolved air flotation. Patents search revealed trends in the dissolved air flotation devices development. A method for increasing the treated fluid aeration by its dispersion at excess pressure is offered. The electrolyte influence on the flotation extraction efficiency is researched. The change in electrolyte concentration influences the bubble coalescence degree, as well as the charge on the particle and the bubble. It is shown that an increase in electrolyte concentration can increase the flotation treatment efficiency. At that, a cheap source of electrolytes is by-products of different processes. In addition, the paper presents data from the regulations in force in the territory of the Russian Federation, on the maximum permitted concentrations of oil products in wastewater. The advantages of dissolved air flotation in comparison with other types of flotation extraction are shown. This paper may be useful to engineers and scientists, whose work involves oil-containing water treatment.

Lamella dissolved air flotation treatment of fish farming effluents as a part of an integrated farming and effluent treatment concept

Nutrient emissions from fish farming can be reduced by a bag pen, i.e., a floating circular basin which serves simultaneously both as a fish cultivation tank and a swirl separation tank. Solid matter (excreta and uneaten feed) is collected at the bottom of the bag pen and pumped as an underflow to a dissolved air flotation (DAF) unit for nutrient removal. DAF equipped with lamella elements was studied in real conditions. Altogether 3000 rainbow trout females (2.0 kg each) were cultivated. Solid–water mixture was pumped from the bottom of the bag pen to an equalizing basin using a sequence of 2-min pumping followed by a 4-min pause. In some tests the influent was pumped directly and continuously from the bag pen to DAF. The influent quality changed substantially: average suspended solids (SS) and phosphorus (P) concentrations were 290 mg l−1±110 mg l−1 and 3.2 mg l−1±1.2 mg l−1, respectively. When the influent was fresh and P strongly associated with SS, DAF without precipitation chemicals produced up to 86% SS and 83% P removals. The influence of chemical doses was studied using 6.4–29.2 mg Fe l−1 with hydraulic loadings (HLs) of 11.0–11.7 m h−1. SS and P removal did not change substantially and the effluent concentration levelled at 30 mg SS l−1 and 0.20–0.30 mg P l−1, respectively. The lamella DAF, coupled with ferric precipitation, produced up to 90% P and 80% nitrogen reductions. HLs, excluding recycle water flow and lamella projection, up to 21 m h−1 could be used.

Reduction of phosphorous at WWTP combined with DAF and A2/O

Regulation of the phosphorous (P) concentration in effluent from the Jinju wastewater treatment plant (WWTP) in southern part of Korea has recently been strengthened, with a reduction in the acceptable P limit from 2.0 to 0.2 mg/L. Various treatment processes have been introduced and applied to meet the regulation, after use of biological treatments such as conventional activated sludge, anoxic–oxic (A/O), and anaerobic–anoxic–oxic (A2/O) treatments. The present work introduces a hybrid system of A2/O and dissolved air flotation (DAF) treatment to remove P from the effluent. The total capacity of the WWTP is 190,000 m3/d. The dimensions of the DAF basins are 8 m (width), 16 m (length), 4.2 m (height), 6 basins, and the capacity is 2,995 m3/d. The retention time and recycling ratio are 19 min and 15%, respectively. The surface loading rate is 240 m/d. Operation of the system with A2/O+DAF has already commenced and total P was reduced from 2.18 to 0.03 mg/L. A2/O+DAF treatment improved the mean effluent concentrations of total phosphorus, chemical oxygen demand, and suspended solids by approximately 70, 29, and 27%, respectively, compared with the corresponding levels in effluent after A2/O treatment alone.

Impact of salinity on coagulation and dissolved air flotation treatment for oil and gas produced water

Produced water is a major wastewater stream in the oil and gas industry which typically consists of dispersed and dissolved oils, and high levels of salinity. Despite concerns that dissolved aromatics in produced water may be detrimental to marine life, discharge regulations and treatment technologies for produced water largely focus on dispersed oil and grease removal. The purpose of this research project was to investigate coagulation with ferric chloride (FeCl3) and dissolved air flotation (DAF) at bench-scale for the removal of both dispersed and dissolved oils from synthetic and offshore produced water samples, with a specific focus on the impact of salinity on the coagulation process. Coagulation and DAF treatment of the produced water samples achieved high removals of dispersed oil and grease, but had limited impact on dissolved aromatics. The coagulation process in the saline produced water samples reduced dispersed oil and grease concentrations from 100 mg/L to below North American discharge limits (i.e. 30 mg/L in Canada, 29 mg/L in the USA) under all conditions tested, while the effectiveness of coagulation treatment in the fresh water synthetic samples was highly dependent on coagulation pH.

Novel Pre-treatement for Dissolved Air Flotation Treatment of Produced Water

Novel Pre-treatement for Dissolved Air Flotation Treatment of Produced Water

Failure Analysis of a Dissolved Air Flotation Treatment Plant in a Dairy Industry

Environmental pollution in Nigeria presents an urgent need to assess wastewater treatment facilities in various industries. This article presents an assessment of dissolved air flotation (DAF) operation in a dairy industry. The industry was visited, wastewater treatment facilities were assessed (based only on efficacy to remove selected environmental health-related pollutants) and measurements of essential design and characterization parameters were taken. The study revealed that the averages of flow rate, biochemical oxygen demand at 5 days (BOD5), chemical oxygen demand (COD), suspended solids (SS) and total solids (TS) of the influent wastewater into the plant (DAF) were 3.45 L/s, 1652.37, 3304.67, 2333.82, and 4396.10 mg/L compared to effluent quality of 560.37, 1127.33, 172.33, and 1866.67 mg/L for BOD5, COD, SS, and TS, respectively. The pH of the wastewater is being adjusted by addition of lime before the effluent equalization tank and individual efficacies of the system were 66.09, 65.89, 65.89, 57.54, 8.68, and 94.49% for BOD5, COD, SS, TS, DS, and total nitrogen, respectively, with overall efficacy of 38.10%. It was concluded that failure (lower overall efficacy) of the system can be attributed to setting of lime in the oversized equalization tank (50 m3 instead of 16.82 m3 per 8 h shift), the lack of application of standardized engineering code and practices (provision of underground tank in the process, lack of complete coagulation processes, coagulation and flocculation units), lack of adequate aeration unit and lack of reliable systems for automatically adjusting dosage of coagulant and flocculant. Although, DAF unit is the centerpiece of a DAF-based system design, there are several other supporting systems important to optimal DAF operation. These observations, coupled with the analysis in this report, demonstrate that the facilities necessary to minimize continuous environmental pollution are lacking. Pollution will become an increasing problem unless pollution preventing codes and standards are developed; incorporated into government regulations and the regulations are enforced.

Treatment of meat industry wastewater using dissolved air flotation and advanced oxidation processes monitored by GC–MS and LC–MS

The meat processing industry generates a large amount of wastewater which represents a serious problem due to their high levels of organic matter which demands effective and high cost treatments. In the present study the effectiveness of the wastewater treatment by dissolved air flotation (DAF) followed by advanced oxidation processes (AOPs) using photo-peroxidation (H 2O 2/UV) and photo-Fenton reactions were evaluated in laboratory scale. The primary treatment was carried out in a DAF system, using optimal dosages of ferric sulfate and coagulation aids. The efficiency of these processes was evaluated through the following parameters: COD, BOD 5, color, turbidity, total solids, fixed solids and volatile solids, both before and after the DAF and AOP treatments. The elimination efficiency of pollutants was monitored by gas chromatography–mass spectrometry (GC–MS) and liquid chromatography–mass spectrometry (LC–MS) analysis. The results had shown that the DAF treatment efficiently reduced the COD, color, turbidity and total solids contents. In addition, the advanced oxidation process increased the organic matter removal of the treated samples. Among the AOPs, the photo-Fenton reaction reached the best overall results. These results show that the DAF process followed by an AOP process might be efficient for meat wastewater treatment, intended or not to water reuse purposes.

Toxicology evaluation of Atlantic Canadian seafood processing plant effluent

The purpose of this study was to carry out an acute aquatic toxicity assessment on select effluent samples from Atlantic Canadian seafood processing plants. Raw effluent acute aquatic toxicity for the flatfish and salmon effluents was assessed using the acute lethality test and Microtox test. The effectiveness of dissolved air flotation treatment (DAF) in removing acute toxicity from these effluents was evaluated using the Microtox test. The salmon effluent failed the acute lethality test using rainbow trout while the flatfish effluent showed acute toxicity in the Microtox test with a 50% inhibiting concentration (IC(50)) of 38.84%. Subsequent treatment by DAF of the flatfish and salmon effluents increased IC(50) values by 20% and 26% respectively. The findings of this study indicate that all of the processing effluents sampled showed characteristics that could potentially degrade effluent receiving waters and acute toxicity was demonstrated in the two raw finfish effluents. Application of DAF treatment was successful in significantly increasing Microtox IC(50) values, thereby reducing acute toxicity, but failed to entirely remove acute toxicity.

Floc Size Distributions in Dissolved Air Flotation of Winnipeg Tap Water

A bench-scale continuous flow dissolved air flotation (DAF) system was operated using Winnipeg tap water. Three different dosages of alum were applied: 41.7 mg l−1, 25.5 mg l−1 and 15.5 mg l−1. Floc size distributions formed at different coagulant dosages were analyzed to identify characteristics of floc size distribution optimal for flotation. Alum dose of 25.5 mg l−1 was found to be optimal for the bench scale DAF unit in this study. At this dosage, the DAF effluent achieved a turbidity of 0.25 NTU and color of 3.8 TCU, significantly lower than that for the tap water. The optimum floc size distribution at the dose of 25 mg l−1 had the logarithmic mean size of 27 μm which was close to the size of air bubbles produced by the saturator in this study (30 μm). The results of this study suggest that the DAF treatment process is optimized when the logarithmic mean floc size and bubble size are equal.

Dissolved air flotation treatment of concentrated fish farming wastewaters

Fish farming wastewaters contain nutrients, phosphorus and nitrogen, which promote eutrophication in the typically shallow farming sites in Finland. Fish farming wastewater treatment is problematic because of large quantities of very dilute wastewater (200-600 m3/kg fish produced). In practice wastewater treatment is concentrated on suspended solids removal. Treatment can be done in two steps: concentration of the very dilute wastewater and subsequent treatment of the concentrated wastewater. Dissolved air flotation pilot trials were conducted using two types of concentrated wastewaters: settled solids from a sludge hopper of a cultivation basin and swirl separator concentrate. Two different pilot plants were used and performances compared. Both mechanical treatment and precipitation by ferric salts were applied. Depending on the influent quality, 70 to 90% phosphorus reductions were achieved without chemicals. Chemical precipitation and flotation produced 90% phosphorus reductions and effluent concentrations at the level of 0.05 mgP/l when 13 m3/(m2h) hydraulic loading was used.

Plywood Mill Water System Closure by Dissolved Air Flotation Treatment

In plywood industry water is mainly needed for soaking the logs. Dissolved air flotation with chemical precipitation was found to be a suitable treatment method for the soaking basin overflow of a plywood mill using birch as raw material. According to pilot treatment studies over 90% reductions of the suspended solids are possible with a hydraulic surface load of 6.5 m3/(m2h). In subsequent experience in full scale following reductions have been achieved: suspended solids 93%, BOD7 50%, CODCr 57%, P 92% and N 52%. Two-thirds of the flotation treated water is led to flue gas scrubbers and circulated back to the soaking basin. Optionally water can be led to the heat recovery, too. One-third of the flotation treated water is disposed of as the mill effluent. Concentrations of organic matter in the system have been reduced after the addition of flotation indicating the possibility of further closure. However, due to the use of aluminium sulphate in coagulation, aeration is needed for sulphate reduction prevention. Further closure of the water system is possible in the future if the heat recovery is renovated, preventing the increase of the water temperature (now 37°C) which otherwise might cause occupational safety hazards.