Drinking Water Dissolved Air Flotation Clarifiers and Thickeners

Dissolved air flotation description

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Dissolved-air flotation processes are designed to enhance the efficiency of solid-liquid separation in wastewater treatment. The core principle revolves around saturating the influent stream with air under high pressure, allowing a significant amount of air to dissolve in the water. Once this water is released into the flotation chamber, the pressure drops, causing the dissolved air to form microbubbles. These microbubbles exhibit a unique ability to attach to suspended particles, leading to effective removal of contaminants.

DAF systems are widely recognized for their ability to mitigate issues related to sedimentation and gravity thickening methods. Unlike traditional methods, which often rely heavily on the weight of solids to facilitate separation, dissolved-air flotation relies on the buoyancy provided by air bubbles. This shift in mechanism results in enhanced removal efficiencies, especially in low-density or finely suspended particles. Consequently, DAF has emerged as a preferred choice across various industries, particularly where space is limited or where rapid treatment times are necessary.

Dissolved air flotation principle

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The overall effectiveness of a DAF unit can often be linked to the efficiency of each individual component. During the pre-treatment phase, the wastewater is first mixed with a chemical coagulant. This crucial step facilitates the aggregation of fine particles into larger flocs, making them easier to separate from the water.

Once the influent feed is adequately treated, it moves into the air dissolving vessel. Here, compressed air is introduced under high pressure to dissolve into the water until the saturation point is reached. This saturation process is essential, as it ensures that when the pressure is released, a myriad of tiny microbubbles form uniformly throughout the flotation tank.

These microbubbles play a pivotal role in the separation process. When the air-water mixture is released into the flotation tank, the dissolved air comes out of solution, forming bubbles that attach to the flocculated particles, giving them buoyancy. The air bubble-particle aggregates rise to the surface, creating a floating sludge layer.

Simultaneously, heavier particles that cannot attach to the bubbles sink to the bottom as settleable solids. This dual mechanism effectively separates the floatable and settleable solids from the water.

The flotation tank’s skimmer system sweeps across the surface to remove the floating sludge, directing it towards a collection trough. This collected sludge can then be processed or disposed of according to regulatory requirements. At the same time, the clarified water, now free of suspended particles, is extracted from the bottom or sides of the tank and moved on to subsequent treatment stages or discharged if it meets quality standards.

The precise operation parameters, such as air-to-solids ratio and hydraulic loading rate, can significantly influence DAF performance. Regular monitoring and adjustments ensure optimal functioning, making the DAF unit a versatile and reliable choice for various wastewater treatment scenarios.

Dissolved air flotation technical sheet

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Dissolved air flotation process flow

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Dissolved air flotation advantage

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There are several distinct advantages of using dissolved-air flotation processes compared to traditional wastewater treatment methods, such as sedimentation. One significant benefit is the ability to effectively treat low-density sludges, which often challenge gravity-based systems. DAF processes can successfully remove suspended solids, oils, and greases more efficiently by leveraging the air flotation technology.

Moreover, DAF systems often require less space than traditional sedimentation tanks due to their compact design and rapid treatment capability. This space-saving feature is particularly beneficial for industries operating in constrained environments or for those looking to modify existing waste treatment setups without extensive infrastructure changes. Additionally, the quick response of DAF systems allows for better control over fluctuating wastewater characteristics, making them ideal for environments with variable loads.

Dissolved air flotation feature

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The environmental impact of DAF systems is generally positive, particularly in minimizing water pollution.

By enabling the removal of over 90% of harmful components from industrial effluents, DAF systems contribute to cleaner water bodies and reduced environmental pollution.

Moreover, reduced chemical usage and advancements in energy-efficient designs further enhance the sustainability of DAF technology.

Dissolved Air Flotation systems have solidified their place as an indispensable tool in modern water treatment processes.

Their ability to efficiently remove suspended solids from diverse wastewater streams makes them particularly valuable across industries with stringent water quality requirements.

As technological innovations continue to evolve, DAF systems are poised to become even more cost-effective and environmentally sustainable, bolstering their role in the global effort to safeguard water resources.

Dissolved air flotation application

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1. Paper mills

Historically, paper mills represent one of the first applications of dissolved air flotation systems. Dissolved air flotation units are used in paper mills for two different applications. The main use is as a process machine: this system allows to recover most of the paper fibers that constitute the raw material and that would otherwise be lost with the cloth washing water.

Secondly, dissolved air flotation units are used for the purification treatment of wastewater, in particular for the removal of suspended solids and the COD linked to them. In both cases, the system is ideal for optimizing the solids recovery yield thanks to the effectiveness of its air dissolving system.

2. Confectionery industries

One of the main applications of the dissolved air flotation system is the pre-treatment of waste water in the confectionery industry. The different production lines are subjected to frequent washing both for hygiene reasons and when products with different characteristics are produced. The process water of the confectionery industry is characterized by high levels of suspended solids, COD and fats.

Dissolved air flotation systems, used as a pre-treatment upstream of a biological treatment, or before discharge into the sewer system, allow these parameters to be substantially reduced. This allows the size to be reduced and the operation of a possible biological plant downstream to be optimized.

Alternatively, a lower polluting load allows companies to discharge their waste water into the sewer system within the values set by the most stringent regulations. The simplicity of management is such that it does not require specialized personnel to operate the system.

3. Cured meat factories

The water coming out of the sausage factories contains high levels of fats and suspended solids, deriving from the meat processing and stuffing process. The presence of these substances can create problems for the biological wastewater treatment plant. Fats inhibit the development of bacterial flora, and the high polluting loads require large-sized treatment plants with long residence times of the wastewater in the biological treatment tanks.

Flotation units intervene on both fronts. Used as a pre-treatment, it allows the removal of fats and suspended solids with extremely high efficiency, thanks to the innovative air dissolving system.

4. Primary and secondary clarification for biological plants

The dissolved air flotation system is widely used as a clarification phase in biological plants of all potentials. Thanks to its high efficiency in removing suspended solids, this solution is useful for the primary clarification of wastewater because it allows the use of extremely small spaces. The efficiency of solids removal is such as to drastically reduce the size of subsequent treatment phases.

For the same reasons, it is also used for secondary clarification, with an additional advantage. The sludge extracted from the flotation unit has a density approximately double that of the sludge extracted from a traditional sedimentation system. This allows for a reduction in the costs of sludge disposal or of creating any sludge treatment line. Furthermore, a denser sludge is recirculated, with obvious savings on the quantity of recirculation and consequently on the size of the oxidation tank.

5. Dairy industries

This is an application very similar to that of salami factories. In these companies, washing occurs very frequently and the waste water is rich in fats and highly biodegradable solid substances. The polluting load is very high and the treatment of this water requires the construction of large plants even when the flow rates involved are relatively low. The flotation unit, in this context, is widely used as a pre-treatment.

Its small size allows it to be installed even on existing plants or in any case where there are space problems. The dissolved air quickly brings solids and fats to the surface, without problems of bad odors and with extremely high removal efficiency. This allows the polluting load to be reduced and therefore the size of the entire plant. Flotation systems are often used even on existing plants that need to be upgraded.

6. Oil & gas industries

Oil depots and refineries are large-scale facilities. Rainwater and runoff water that falls on yards and buildings must necessarily be treated before being discharged. In addition to this, there is also the displacement and washing water in general. A peculiar characteristic of these waters is the presence of considerable quantities of oil. Dissolved air flotation units are effective solutions for their removal.

Flotation certainly has the advantages of removal efficiency, small dimensions, and the possibility of inserting the machine into the context of an existing plant. If the company already has its own biological purification plant, the system allows for an increase in efficiency by removing upstream all substances that could inhibit the correct functioning of the biological process.

7. Textile industries
The waters coming out of these companies are rich in fibers that escape from the various washing processes to which the raw wool is subjected. The raw material is rich in solids, fats and organic substances, which are removed with the washing waters. In the waters there are also abundant quantities of surfactants deriving from the detergents used for washing.

Dissolved air flotation systems have proven to be effective systems for the treatment of these waters, upstream of any biological and/or chemical-physical processes. They allow the removal of approximately 80% of the fats and solids contained in the waters, and also carry out a partial reduction of the surfactants linked to the latter. The micro air bubbles that are generated in the saturator and that are released in the flotation tank are so fine that they do not cause the formation of foam despite the high levels of surfactants.