【Dry goods】If the suspended solids in wastewater are too high, will flotation be effective?-Hezhong Environment (Beijing) Co., Ltd. was established in 2003

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【Dry goods】If the suspended solids in wastewater are too high, will flotation be effective?

Published Time:

2025-06-27

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Friends often ask me: "The wastewater is full of suspended solids, like mud. Can dissolved air flotation really save it?" To be honest, this question is like asking, "Can cold medicine cure a headache?" - It depends on the specific situation! Today, let's break down the principles of dissolved air flotation, what kind of wastewater it can easily handle, and what kind requires other solutions.

Let's talk about how dissolved air flotation works. Simply put, it's like a "water rescue operation." We inject a bunch of tiny bubbles into the wastewater. These bubbles are like small life preservers, desperately rising to the surface. If the suspended solids in the water can "hold on" to these bubbles, they can float to the surface with the bubbles and finally be removed by a skimmer. Imagine pouring a glass of water mixed with sand into a swimming pool, and suddenly a bunch of small balloons bring all the sand to the surface. Isn't that amazing?

From the principle, dissolved air flotation is indeed effective against suspended solids. First, it is particularly effective for suspended solids with a density close to or slightly heavier than water. For example, dye particles in dyeing wastewater and protein flocs in food processing wastewater. These "little guys" originally wouldn't sink in the water, but once the bubbles hook up with them, they can go ashore together. Some emulsified oil wastewater has oil droplets dispersed in the water like small pearls. Dissolved air flotation allows the bubbles to string them into "pearl necklaces," directly floating to the surface.

In practical applications, dissolved air flotation has shown good results. Take wastewater from paper mills, for example. It's full of broken fibers and fillers. Sedimentation treatment might take half a day, and the fibers may still not settle completely. But with dissolved air flotation, most of the suspended solids can be removed in ten minutes, leaving the water clear enough to see the bottom. Another example is slaughterhouse wastewater, where blood and meat scraps are mixed together. After dissolved air flotation treatment, not only are suspended solids significantly reduced, but the pressure on subsequent biological treatment is also greatly reduced. Many wastewater treatment plants use dissolved air flotation as an "appetizer," first removing large suspended solids, so that subsequent treatment processes can be "lighter".

However, dissolved air flotation is not a panacea. If the suspended solids in the wastewater are particularly heavy, such as large-particle gravel in construction sludge, even with the bubbles' best efforts, it's difficult to bring them up. In this case, sedimentation is more reliable. Some suspended solids have very smooth surfaces, and the bubbles cannot "grab" them, such as certain high-molecular-weight particles in chemical wastewater. This requires adding some reagents in advance to make the particle surface rougher, increasing the "friction" with the bubbles.

In addition, the effectiveness of dissolved air flotation also depends on the operational details. The size of the bubbles is key. Bubbles that are too large have strong buoyancy but have a small contact area with the suspended solids; bubbles that are too small are prone to coalescing into large bubbles. Generally, a bubble diameter of 10-100 micrometers is optimal. This is like finding a life preserver for suspended solids; the size must be appropriate to hold on tight. The amount of reagent added must also be precisely controlled. Too little will result in poor flocculation, while too much will create new pollution.

If the dissolved air flotation treatment is not ideal, don't panic. First, check if the influent water quality has suddenly deteriorated. For example, the upstream production line temporarily changed its process, and the nature of the discharged suspended solids changed. It may also be that the equipment has malfunctioned, such as insufficient pressure in the dissolved air tank, resulting in insufficient bubble production; or the skimmer speed is too fast, and the suspended solids are scraped away before they have fully floated. These minor problems need to be checked one by one.

In general, dissolved air flotation for treating wastewater with high suspended solids is like hiring a "water cleaner." As long as the wastewater properties are suitable and the operation is proper, it will definitely produce excellent results. However, if you encounter "stubborn" wastewater, don't stick to it. Combine it with other methods such as sedimentation and filtration to create a "combination punch" to ensure that the wastewater is treated properly! Next time someone asks you if dissolved air flotation works, you'll know much better, right?