In industrial wastewater treatment projects, dissolved air flotation (DAF) systems and sedimentation tanks both perform solid-liquid separation. However, the choice is not simply a matter of determining which one is better. DAF systems primarily use microbubbles to float suspended solids, oil and grease, and flocculated particles to the water surface, where they are removed by a skimming device. A lamella clarifier, by contrast, uses the density difference between particles and water, allowing settleable solids to sink under the force of gravity.

The final selection of solid-liquid separation equipment depends on several factors, including the characteristics of the pollutants, flocculation performance, influent flow rate, fluctuations in water quality, available space, and downstream treatment processes.

For wastewater containing oil, colloids, and large amounts of low-density suspended solids, DAF systems are generally more suitable. For well-settling flocs and relatively stable water quality, Lamella clarifier are often easier to operate as a continuous and cost-effective treatment unit. In practical industrial wastewater treatment projects, DAF systems and Lamella clarifier can also be used in combination according to the specific characteristics of the wastewater.
 

Different Working Principles

How Dissolved Air Flotation (DAF) Works

A dissolved air flotation (DAF) system introduces a large volume of fine bubbles into the wastewater through dissolved-air saturation, air release, or other microbubble-generation methods. After coagulation and flocculation, the bubbles attach to the surfaces of suspended solids, oil droplets, or flocs. This reduces their overall density and causes the pollutants to float to the water surface. A skimming mechanism then collects and removes the floated solids, while the clarified water at the bottom flows to the next stage of wastewater treatment.

This separation method is particularly well suited to wastewater containing oil and grease, emulsified substances, colloids, lightweight suspended solids, and certain flocs that are difficult to settle naturally. The performance of a DAF system depends not only on the flotation unit itself, but also on chemical dosing and mixing, the flocculation reaction, the air bubble system, the skimming mechanism, and the design of the sludge and scum removal systems.

If the upstream water-quality analysis and chemical testing are inadequate, even a DAF system with sufficient design capacity may experience unstable scum formation, fluctuating effluent quality, or excessive chemical consumption.

How a Lamella Clarifier Works

A lamella clarifier relies on gravity to gradually settle settleable particles in the wastewater. Solid-liquid separation is completed through sludge collection and sludge removal structures. Common sedimentation configurations include horizontal-flow, vertical-flow, and radial-flow tanks, as well as enhanced settling systems that use inclined plates or inclined tubes.

The operating performance of a sedimentation tank is closely related to particle settling velocity, surface loading rate, water-flow distribution, floc strength, and the timeliness of sludge removal. When coagulation and flocculation produce dense flocs with good settling characteristics, a lamella clarifier or conventional sedimentation tank can serve as a stable pretreatment or polishing unit in an industrial wastewater treatment system.

Compared with the dissolved air flotation process, sedimentation tanks generally do not require the continuous generation of microbubbles. However, the tank dimensions and hydraulic retention space must be properly configured according to the design conditions. If the wastewater primarily contains colloids, oil and grease, or low-density particles, gravity sedimentation alone may not achieve the expected solid-liquid separation performance.

Make the Right Equipment Selection with Yimei

Drawing on extensive experience in wastewater treatment projects, Yimei helps customers make more accurate equipment-selection decisions. Detailed 3D drawings provide valuable support by enabling customers to clearly understand the final system configuration and expected results before the project begins.

Material Comparison: Choosing the Right Equipment for Industrial Wastewater Treatment

Corrosion resistance and the project environment should be considered first. Equipment material is not simply a matter of price; it is a key factor that determines service life, maintenance frequency, and operating stability. Both dissolved air flotation (DAF) systems and lamella clarifiers may come into contact with acids, alkalis, salts, oil and grease, organic solvents, or chlorine-containing media. Therefore, material selection should be based on a comprehensive evaluation of the wastewater composition, temperature, concentration, installation environment, and cleaning method.

Carbon Steel: Suitable for Projects Focused on Strength and Cost

Carbon steel offers good structural strength and is easy to process, making it suitable for large equipment bodies, support structures, and some conventional industrial wastewater treatment equipment. For projects where water-quality corrosivity is relatively controllable, an appropriate anti-corrosion coating, proper surface treatment, and regular inspections allow a carbon steel solution to balance equipment strength and initial investment.

However, a carbon steel corrosion-protection system is not permanently effective after a single application. When equipment is exposed to wastewater with high salt content, strong acidity or alkalinity, or corrosive chemicals over an extended period, the coating may wear or age. Therefore, when selecting a carbon steel DAF system or carbon steel sedimentation tank, buyers should also confirm the anti-corrosion process, weld treatment, inspection and maintenance method, and conditions for subsequent repainting. The comparison should not be based only on the price of the uncoated equipment.

Yimei places great importance on anti-corrosion surface treatment and has specifically developed high-performance protective coatings to address corrosive operating conditions and help extend equipment service life.

Stainless Steel: Suitable for Applications with Higher Corrosion-Resistance and Cleanliness Requirements

Stainless steel equipment generally provides better corrosion resistance and surface stability. It is suitable for environments such as food processing, pharmaceuticals, chemicals, and precision manufacturing, where hygiene, resistance to process media, or appearance is especially important. Different stainless steel grades have different levels of resistance to acids, alkalis, salts, and specific chemical media. Material selection must therefore be confirmed according to the actual water quality rather than based on the general assumption that all stainless steel is suitable for every application.

For dissolved air flotation systems, stainless steel can be used for the main equipment body, water-contact components, or areas that are more vulnerable to corrosion. For lamella clarifiers, the choice between an all-stainless-steel structure and corrosion-resistant materials in selected critical areas can be made according to the tank dimensions, characteristics of the process media, and project budget. Selecting materials by zone can help balance reliability and investment.

Treatment Capacity Comparison: Do Not Select Equipment Based on Flow Rate Alone

During the initial procurement stage, many projects only request information on “how many tons of water can be treated per day.” However, design flow alone is not sufficient for accurate equipment selection. The treatment capacity of a dissolved air flotation system or lamella clarifier depends not only on influent flow, but also on pollutant concentration, solid-particle characteristics, coagulant and flocculant performance, required effluent standards, and operating cycle. Wastewater with the same flow rate may require completely different equipment dimensions and process configurations because of differences in water quality.

DAF system selection typically requires attention to the rated treatment flow, peak flow, air bubble system capacity, scum-removal load, suspended-solids and oil-and-grease load, chemical dosing and reaction conditions, and the water content of the floated scum. For factories with significant fluctuations in wastewater volume, production hours, discharge periods, and short-term peak flows should be included in the design instead of relying only on the average daily flow. If the influent contains large amounts of oil and grease, emulsified substances, or lightweight suspended solids, the separation efficiency and scum-removal capacity of the flotation section should also be carefully verified.

The advantage of dissolved air flotation lies in its ability to rapidly separate floated solids within a short period and its relatively compact equipment arrangement, as well as its adaptability to low-density pollutants. However, as treatment capacity increases, greater attention must be paid to influent uniformity, the stability of the dissolved-air or microbubble system, continuous skimming performance, and the connection with sludge handling and disposal. Equipment capacity should not be assessed separately from the complete wastewater treatment process.

The treatment capacity of a lamella clarifier is closely related to surface loading rate, hydraulic retention time, effective settling area, influent and effluent arrangement, sludge concentration, and sludge-removal frequency. For flocs that settle easily, an appropriate hydraulic design can help a lamella clarifier maintain stable operation. For fine particles, particles with a density close to that of water, or pollutants that tend to float, separation conditions may need to be improved through coagulation, flocculation, inclined plates, or inclined tubes.

When the treatment scale of a lamella clarifier is expanded, the tank footprint, structural strength, sludge-scraping or sludge-removal method, and potential short-circuiting of water flow must all be included in the design. If sludge is not removed in time, accumulated sludge may become anaerobic, float to the surface, or re-enter the water, resulting in higher suspended solids in the effluent.

Which Applications Are Better Suited to DAF?

DAF systems are better suited to wastewater containing oil, emulsion wastewater, food-processing wastewater, textile dyeing wastewater, papermaking wastewater, and industrial wastewater with large amounts of colloids and lightweight suspended solids. For these water-quality conditions, when pollutants are difficult to settle naturally, the dissolved air flotation process can strengthen solid-liquid separation through microbubbles. DAF systems are also commonly used when rapid scum removal is required, when the organic or solids load on downstream biological treatment needs to be reduced, or when pretreatment performance needs to be improved.

Which Applications Are Better Suited to a Lamella Clarifier?

Lamella clarifiers are better suited to wastewater in which coagulation produces relatively large flocs, sludge-water separation after biological treatment, wastewater with a high content of inorganic particles, and process stages that require continuous settling and sludge collection. When site conditions are suitable, pollutant settling performance is stable, and the project places greater emphasis on continuous operation and integration with sludge thickening, a lamella clarifier is generally worth evaluating as a priority.

If the wastewater contains oil and grease, colloids, and settleable particles at the same time, selecting only one type of equipment may not address all the pollutants.

Information to Confirm During Equipment Selection

First, confirm the flow rate used for equipment design, including the average flow, maximum flow, instantaneous peak flow, and daily operating hours.

Second, provide as much complete water-quality information as possible, including pH, suspended solids, oil and grease, COD, salinity, temperature, and any potentially corrosive media.

Third, ask the supplier to explain the basis used to calculate the equipment treatment capacity. Where conditions permit, verify the flotation or sedimentation performance through wastewater sample testing.

When selecting an equipment manufacturer, it is also important to determine whether the supplier understands both DAF and lamella clarifier processes. If a supplier has limited experience or provides only one type of equipment, the project design may be restricted by its product range. A manufacturer capable of providing complete wastewater treatment equipment and production services is better positioned to offer an integrated solution from the perspectives of water quality, process flow, materials, and equipment integration.

Since 1998, Yimei has provided accurate, one-stop solutions for numerous overseas markets. The technical team offers on-site assessment services to optimize systems and ensure compliance and efficiency.

Analyze the Water Quality Before Choosing DAF or a Lamella Clarifier

Dissolved air flotation and lamella clarifiers each have their own suitable applications. DAF systems are effective for treating oil and grease, colloids, lightweight suspended solids, and difficult-to-settle flocs, while lamella clarifiers are better suited to particles and flocs with stable settling performance. Material selection should focus on the corrosive environment, structural strength, and maintenance conditions. Treatment capacity should be evaluated by considering flow rate, water quality, peak loading, flocculation performance, and continuous operating requirements together.
 

If you are looking for a suitable one-stop solution for an industrial wastewater treatment project, contact Yimei. Our technical team will respond within 24 hours.