High-rate Dissolved Air Flotation Research Articles

Pilot-scale study on the performance of high-rate DAF based on removal of organic precursors and formation characteristics of disinfection by-products

In recent years, there has been an increased focus on the design and development of dissolved air flotation (DAF) with a high surface loading rate (SLR), but little research has been conducted using advanced natural organic matter characterization techniques. This research thus investigates the performance of pilot-scale DAF (10–30 m h–1) and compares them with those for a full-scale coagulation–flocculation–sedimentation (CFS) system based on the reduction of organic precursors, different molecular weight (MW) fractions characterized by liquid chromatography with organic carbon detection, and disinfection by-products. The removal of dissolved organic carbon (DOC) decreased with increasing SLR, ranging from 29 % to 38 %. This may be because of the short flocculation retention time for high SLR. Thus, achieving a similar removal of DOC by high SLR required higher coagulant doses. Furthermore, the organic precursors were measured lower in the high-rate DAF effluent than the CFS, maybe because of the high coagulation pH of the CFS effluent (7.5–8). Similarly, the concentration of different MW fractions, especially biopolymers and building blocks, was lower in the high-rate DAF effluent than in the CFS. The removal of biopolymers was 74.64 % and 87.20 % for the CFS and high-rate DAF, respectively. Likewise, 2.78 % and 27.09 % for the CFS and high-rate DAF, respectively, for building blocks. The normalized trihalomethanes/DOC and chloralhydrate/DOC were higher for the CFS than the high-rate DAF. Coagulation chemistry (pH, coagulant doses, and retention time) strongly influences the DAF and CFS unit performance and should not be neglected.

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 30m/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±0.37μg/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.

Treatment and water reuse of lead-zinc sulphide ore mill wastewaters by high rate dissolved air flotation

Simulated wastewaters (concentrate and tailings thickener overflows), from a future lead-zinc flotation separation plant, were treated for the removal of target metal ions (Zn2+, Pb2+ and Cu2+) and suspended solids (0.1–0.5 g L−1). The ions were adsorbed onto ferric hydroxide precipitates, and then removed by dissolved air flotation (DAF). Best results obtained at bench scale were validated at pilot scale, employing i. 15–20 mg L−1 Fe3+ (chloride salt); ii. Flocculation in two units (rapid mixing - G > 120 s−1, and slow mixing - G = 20–80 s−1), with 0.2–0.5 mg L−1 of flocculant (a cationic polyacrylamide); iii. DAF at a saturation pressure of 6 bar and a 20% water recycling rate. The removal of ions between pH 6.5 and 7.5 was very high, reaching separation efficiencies up to 95% for Pb2+ and Cu2+ ions (potential activators of ZnS); the adsorption mechanisms of the uptake of the ions were discussed. The suspended solids (fine particles, <44 µm) were separated by DAF (89–96%) to concentrations <0.5 g L−1. For higher solid contents, the formed flocs became larger, difficult-to-float and operating conditions required less flocculant and a higher recycling ratio. These high separation efficiencies allowed reuse of water in the lead/zinc sulphide ore rougher flotation stage, avoiding the activation of ZnS flotation. The pilot DAF unit (1.8–2.4 m3 h−1 flow rate) followed an innovative design by enhancing the height/area rate (6.9 m−1), compared to conventional cells; it included specially designed and oriented lamellae and a perforated plate to control internal turbulence. These modifications allowed the enhancement of the hydraulic loading capacity up to 15 m3 m−2 h−1 (or 15 m h−1), more than double the known value for conventional DAF cells (about 7 m h−1). Estimations of general costs for a 300 m3 h−1 treatment plant were calculated and the operating costs reached US$ 0.56 m−3 of treated water. It is believed that this DAF process has a high potential for removing deleterious ions from water at a high removal rate, recycling process water feeding ore flotation plants and minimizing effluent discharge (sometimes polluted).

Recovery of particulate matter from a high-rate moving bed biofilm reactor by high-rate dissolved air flotation

Abstract High-rate biological wastewater treatment processes for carbon recovery are able to improve the energy balance and carbon footprint of water resource recovery facilities. Combination of a high-rate moving bed biofilm reactor (HR-MBBR) with a rapid flotation (HR-DAF), as a replacement for the ‘A stage’ of the A-B process, can achieve this objective. The main goal of this study was to maximize the capture of biodegradable particulate matter from an HR-MBBR effluent by an HR-DAF. A pilot-scale HR-DAF process was operated downstream of an HR-MBBR treating screened municipal wastewater. The particulate biodegradable matter recovery was evaluated by determining the total suspended solids (TSS) removal efficiency. TSS recovery in experiments without chemicals at low surface loading rates (&amp;lt;15 m/h) and high recycle ratio (&amp;gt;25%) was 94 ± 1%. By using a tannin-based polymer, the solids capture efficiency of the HR-DAF was slightly improved with TSS recovery reaching 96 ± 1% at a high SLR (at least 22 m/h) and low recycle ratio (14%). The anaerobic biodegradability of the tannin tested was determined to be 17%. The HR-DAF process downstream of an HR-MBBR gave a very good particulate matter recovery that offers a promising alternative to the A-B process for carbon recovery.

High Rate Dissolved Air Flotation (DAF) for the Removal of Algae Species

High Rate Dissolved Air Flotation (DAF) for the Removal of Algae Species

Feasibility study of high-rate dissolved air flotation process for rapid wastewater treatment

One advantage of the flotation system is its high applicability as a compact facility. Recently, research for the introduction of additional high-rate dissolved air flotation (DAF) into conventional water treatment plants has been progressing in areas of remodeling water treatment plants, advanced treatment, and combined sewer overflow (CSO) treatment. For successful design and operation of high-rate DAF, laboratory experiments to verify model results and estimate standard values of major parameters by model simulation were performed in this study. With the model simulation having a population balance concept, an operational analysis of bubble-floc aggregates considering a hydraulic situation in the separation zone during high-rate DAF was conducted. Based on the model simulation results, a basic level for high-rate DAF design at a hydraulic loading rate of 30 m/h was determined. On the basis of population balance theory, it can describe the process of bubble-floc aggregate formation at a contact zone and calculate the rate of transfer into the separation zone.

Optimization of water treatment plant flow distribution with CFD modeling of an influent channel

In the design of water and wastewater treatment plants, proper flow and solids distribution can be as critical as process design considerations. Insufficient treatment and even plant failures can result from unequal and unmanageable flow and solids distribution. Computational fluid dynamics (CFD) modeling is a valuable tool in the evaluation of flow distribution to multiple units within a treatment process. This article reviews the benefits achieved by performing a CFD analysis of an Infilco high-rate dissolved air flotation (DAF) influent channel prior to finalizing the design of the plant. The CFD model was used to optimize the DAF influent channel configuration with respect to flow distribution to 10 identical process units that were inserted into an existing facility footprint. For the initial configurations modeled, the largest deviation of flow rate to an individual DAF unit was over 60%. Using CFD, design engineers developed a DAF influent channel configuration predicted to achieve less than 10% deviation. The upgraded facility is constructed and in service and the results of the CFD model were confirmed using actual turbidity data, which indicate that the solids are evenly distributed to the DAF process trains.

SWRO pre-treatment design using high-rate dissolved air flotation including preliminary pilot-scale results

The purpose of this paper is to present an overview of the design for both the full-scale and pilot-scale seawater reverse osmosis (RO) pre-treatment plant comprising dissolved air flotation (DAF) and dual-media filtration (DMF) proposed and operating, respectively, at the Ras Al Khair site in Saudi Arabia. This paper will deal with the design implications for a high-rate DAF and DMF plant, rated at a net loading of 30 m/h and up to 6.5 m/h, respectively, processing a proposed feed flow of approximately 1,010 Ml/d, and then how to replicate this using a pilot plant. In addition, how water conditions such as high salinity and temperature and the physical characteristics of the plant impact the process design. The basic water chemistry requirements and the physics when applying dissolved air will be discussed. In the latter case this involves both the dissolving and the subsequent efficient release as fine micro-bubbles of the air, to ensure that the required level of clarification is achieved ahead of filtration and that an SDI15 of <4 is consistently delivered to the RO plant.

Long-term Comparison Testing with Sand Ballasted Flocculation (SBF) and High-rate Dissolved Air Flotation (DAF).

This paper reports on the investigation conducted by Antwerp Water Works (AWW) in Belgium to make a long term (12 months) comparison between SBF and high-rate DAF to determine which process would be optimal. Three major objectives where put forward at the beginning of the study: technology comparison, gain operational experience and conduct coagulant testing. This paper discusses the result obtained with respect to these objectives. Overall this paper clearly points to the value this type of piloting can bring to water companies.

Developments of high rate dissolved air flotation for drinking water treatment

Research Article| September 01 2007 Developments of high rate dissolved air flotation for drinking water treatment James K. Edzwald James K. Edzwald 1Department of Civil and Environmental Engineering, Clarkson University, Potsdam, NY, 13699-5710, USA E-mail: jedzwald@clarkson.edu Search for other works by this author on: This Site PubMed Google Scholar Journal of Water Supply: Research and Technology-Aqua (2007) 56 (6-7): 399–409. https://doi.org/10.2166/aqua.2007.013 Article history Received: April 05 2007 Accepted: June 19 2007 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Cite Icon Cite Permissions Search Site Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll JournalsThis Journal Search Advanced Search Citation James K. Edzwald; Developments of high rate dissolved air flotation for drinking water treatment. Journal of Water Supply: Research and Technology-Aqua 1 September 2007; 56 (6-7): 399–409. doi: https://doi.org/10.2166/aqua.2007.013 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex Since the mid 1990s there has been a large increase in the hydraulic loading rates used to design dissolved air flotation (DAF) facilities for drinking water applications. High rate DAF processes are now available at loading rates of 20 to 40 m h−1. These high rate systems have a smaller plant footprint compared to conventional systems. The paper examines bubble and floc-bubble rise rates, and how the simple theory relating these rise rates to the hydraulic loading of the DAF separation zone is inadequate. It is shown for high rate systems that the flow through the separation zone is stratified and must be accounted for in relating separation zone efficiency to the hydraulic loading and bubble or floc-bubble rise rates. A conceptualized stratified flow model is used to explain why DAF tanks can be designed with hydraulic loadings >20 m h−1. bubble rise rates, dissolved air flotation, drinking water, floc-bubble rise rates, high rate flotation, separation zone This content is only available as a PDF. © IWA Publishing 2007 You do not currently have access to this content.

The El Coloso (Chile) reverse osmosis plant

Degrémont was awarded in 2004 the construction of a 45,360 m 3/d reverse osmosis desalination plant for Minera Escondida Limitada (MEL). This plant is part of its Sulphide Leach Project which aims at increasing its production. The new plant is located on the North Coast of Chile at MEL facilities of Coloso Port, 15 km south of Antofagasta city. The desalinated water produced on site will then be pumped to the second largest open-pit copper mine in the world, 170 km away from the coast and up to an altitude of 3200 m above the sea level. This desalination plant will be the largest one in South America. The treatment line includes one of the most complete and efficient pre-treatments including grit removal, high rate dissolved air flotation (AquaDAF™), two stages of pressurized dual-media filtration and cartridge filters (5 μm nominal cut-off). This complete pre-treatment line has been required since the water quality of the North Coast of Chile could suffer, all-year round, from high algae and TOC concentrations. The poorest water quality has been observed during “red-tides” events (red algae bloom). This design has been confirmed by lab-scale tests performed on-site in 2004 and by the feedback of two small SWRO plants providing water for two thermal plants in the same area (Mejillones and Atacama). The pre-treatment of these two SWRO plants is a combination of a conventional DAF followed by a single stage/single media filtration. It gives satisfying results concerning clarification, nevertheless it could not maintain, most of the time, a SDI below 3%/min highlighting the necessity of an even more complete pre-treatment line as it had been anticipated. The reverse osmosis stage will be operated at a high recovery rate of 50%. It consists of a single pass with 4 trains of 137 pressure vessels each. Pressure vessels are filled with 7 FilmTec seawater 8″ elements but a special membrane arrangement (hybrid) has been decided. The first two elements in the pressure vessels are of “high rejection” type and the five following ones are of “standard” type. This peculiar arrangement has been chosen to maintain a correct flow pattern throughout the pressure vessel for the whole range of temperature (11–23°C) and with a changing feed pressure over the year due to the high recovery rate. Consequently, it provides a narrower flux distribution and a better permeate quality without affecting significantly the feed pressure. In addition, the design includes an energy recovery system consisting of Pelton turbines. Finally, flotation's sludge and filters' wash water are treated to meet the permitted suspended solids discharge concentration. From February to September 2005, a pilot-scale study has been conducted on site. The purpose of the study was: to demonstrate the relevancy of our design and to validate its efficiency whatever the raw water quality; to fine-tune the treatment according to the different raw water qualities in order to improve the commissioning of the full-scale plant. The pilot treatment line is representative of the full scale one with a production capacity of pre-treated water of more than 500 m 3/h for a desalinated water production of 250 m 3/h. Throughout the test period, the pilot plant has achieved to produce pre-treated water with a SDI between 2 and 3%/min more than 90% of the time, even during a “red-tide” period. These results prove the efficiency of the selected pre-treatment line especially with poor raw water quality. Moreover, RO operation at a high recovery rate of 50% has shown no flux, salt rejection nor pressure variation during the period of the test meaning that there was a low organic and mineral fouling rate. It is expected that this optimal pre-treatment design and this combination of membrane will allow a high recovery rate together with a low permeate salinity over the temperature range experienced at El Coloso site.

Reverse osmosis on open intake seawater: pre-treatment strategy

Pre-treatment of seawater feeding reverse osmosis (RO) membranes is a key step in designing desalination plants. The pre-treatment process must be adapted to the seawater quality to be treated (wells, open intake, etc.), especially when treating surface seawater with highly variable quality. After a general presentation of different pretreatment options in relation to the seawater quality, this paper is focussing on two case studies, two open intake seawater pre-treatment upstream reverse osmosis desalination. The first site is located in the Gulf of Oman (Indian Ocean), the second in the Persian Gulf. The pre-treatment uses different technology strategies, conventional pretreatment (coagulation and direct filtration on dual media filters) and innovative technologies (high rate dissolved air flotation, ultrafiltration and microfiltration) according to the water quality. The parameters taken into account for the water quality characterisation are the suspended solids, turbidity, fouling tendency, organic matters and algae content. This paper presents the pre-treated water quality achieved by the two types of pre-treatment and discusses potential impacts on RO hydraulic performances.

High-rate dissolved air flotation for water treatment

This paper presents the results of an experimental investigation about the performance of a horizontal flow high-rate pilot scale Dissolved Air Flotation (HRDAF) unit containing inclined parallel plates for treating a coloured and low turbidity raw water. Experiments were performed with the DAF unit in order to verify the influence on flotation of: (i) the water velocity (Vh) between the plates, in the range 18 to 96.5 cm.min-1 with corresponding Reynolds numbers between 240 and 1060; (ii) the supplied air (S*) value ranging from 2.2 to 8.5 g of air/m3 of water; (iii) the angle of the plates (60 degrees or 70 degrees). The best pilot plant operational condition was obtained applying only 4.0 g/m3 (S*) with Vh around 18 cm.min-1 for treatment of water coagulated with a Al2(SO4)3 dosage of 40 mg.l-1. In these conditions, the unit presented very good removal efficiencies of colour (90%, residual of 10 uC), turbidity (88%, residual of 0.8 NTU) and TSS (94%, residual of 1.8 mg.l-1). Furthermore, the unit could operate at higher Vh values up to 76 cm.min-1 and still present good results. The DAF unit thus behaved as a high rate unit presenting good performance with low air requirement.