Clarification Principles In Separation in Wastewater Treatment

Clarification means removing suspended solids from liquids. It forms a part of the purification of water and this treated water has many applications. Plants generally use clarifiers for this.  Clarifiers are settling tanks and so are often also are called settlers.

When the wastewater enters the treatment system it usually undergoes coagulation and flocculation processes first. The aim is to separate out solids from the water. These solids may be floating or suspended in the water. Coagulation causes the fine suspended molecules to clump together, then large mechanical paddles allow the coagulates to form denser particles or flocs that settle more easily. The flocs sink to the bottom of the tanks and can be easily collected. Any scum floating on the top can also be removed. The partially treated water then undergoes clarification. Sometimes chemical thickeners are added.

The stream of water then goes to the clarifier where the separation of clarified liquid from the solids and flocs occurs by letting the heavier and larger particles settle to the bottom.

Clarifiers usually feature a built-in mechanism for the continuous removal of the solids deposited by sedimentation. Concentrated impurities discharged from the bottom of the tank are known as sludge while the particles that float to the surface of the liquid are called scum. Most commonly, a clarifier comes in a circular design but rectangular and other configurations also are available.

Clarifiers usually incorporate mechanical solids-removal devices that move as slowly as practical to minimize resuspension of settled solids. The clarified liquid often is pumped to filters to eliminate any residual particles; the filtered liquid then flows on to the next process.

The particles need to settle – and disturbance of the water or too fast a flow will inhibit settling of the sludge. Considerable attention is focused on reducing liquid inlet and outlet velocities to minimize turbulence. Turbulence inhibits settling. Baffles prevent the movement of water at the entrance to the tank from extending further into the tank. Overflow weirs distribute the flow from liquid leaving the tank uniformly over a wide area of the surface to minimize re-suspension of settling particles.

Design and Operation of Clarification

Control of liquid flow into a clarifier is important. A slow rate of flow increases the hydraulic retention time inside the clarifier. This makes settlement and sedimentation more efficient since any excessive turbulence and mixing is minimised. The inlet flow also should be distributed evenly across the entire cross-section of the settling zone inside the clarifier; as a very rough indication, the settling zone’s volume often is around 30–40% of the total capacity of a clarifier.

During Clarification the sludge formed from the settled particles at the bottom of the clarifier, if left for an extended period, may become gluey and viscous, creating difficulties in its removal. Using gas (or other means) to free the sludge can cause the re-suspension of particles throughout the liquid, reducing the effectiveness of the clarifier. This sludge should be drained properly from the bottom of the tank — usually, this involves using specially designed positive-displacement pumps.

Two dominant forces act upon the solid particles in clarifiers: gravity and particle interactions. Too high a flow can lead to turbulence, hydraulic instability and potential flow short-circuiting. Improvements and modifications made during the last few decades, particularly for improving the separation process, have enhanced clarifier performance. For instance, the installation of specially designed perforated baffle walls (based on advanced hydrodynamic simulations) promotes flow uniformity.

The clarifier mechanism is designed for constant operation, the flow usually enters the centre draft tube through a horizontal influent pipe extending from the tank sidewall.

Enduramaxx’s Clarification Tanks

Our Clarification Tanks are used for the continuous mechanised removal of suspended solid particles from a liquid. The clarification principles separation is also involved with conical or cone-bottomed clarification tanks. They are available in a range of sizes.

Enduramaxx polymer mixing tanks, also known as agitators, may prove an economical and effective solution for the manual preparation systems for powder polymer mixers. they are an essential part of industrial process engineering – from the smallest plant room to a clean-in-place system for an entire factory. Mixers for these polymer mixing vessels are designed as a low-speed mixer, for water treatment with viscous fluids, with options of single or three-phase motors available with stainless steel shafts.

We can offer various tanks as shown below:

These are all part of the primary wastewater treatment.

If you would like to speak to our experts please give us a call to discuss further.

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