Wastewater is a combination of water, suspended particles, grease, organic waste and other pollutants that can't be eliminated with a single process. A wastewater clarifier aids in separating many of those solids from the liquid so that the water can proceed through following treatment operations with a lower sediment load. It is a critical component of many municipal and industrial treatment systems where settling is utilised to separate materials by density.

Grasping what happens inside a clarifier also assists in understanding how the design, operation and maintenance of a clarifier can impact the performance of a complete treatment plant.

Where Does Clarification Fit Into Wastewater Treatment?

The stages of wastewater treatment vary slightly from one facility to another depending on the wastewater being treated and the intended effluent quality. Typical treatment processes include screening, grit removal, primary clarification, biological treatment, secondary clarification, filtration, and disinfection.

So clarification is not an independent operation. It operates as a sequence with every step preparing the effluent for the next step.

Screens and grit-removal equipment can remove bigger debris and dense particles such as sand and gravel before primary settling. Once these materials are removed, the wastewater can be directed to a settling tank where the suspended material can settle out.

How Does a Wastewater Clarifier Separate Solids?

The basic idea is simple enough: give the wastewater time and the right conditions to let the heavier suspended solids settle down .

As the wastewater goes through a clarifier, the heavier solids settle out slowly settling to the bottom of the clarifier creating sludge. Materials lighter than water, such as fats, oils and grease, will float to the surface and can be skimmed off as scum. The cleared liquid between these layers can subsequently be subjected to a further step of treatment.

Mechanical components aid in removing the separated materials so they do not build up forever inside the tank. The success of this operation is a function of hydraulic conditions, settling characteristics, loading and design of the equipment.

What Happens to the Sludge?

Settled sludge should be collected and managed in place of leaving it in the tank. Depending on the treatment facility, it may be subjected to further processing, treatment, dewatering, disposal or other forms of resource management.

The need for consideration of clarity and sludge handling combined. Settling might be impeded and mechanical equipment overloaded due to poor sludge removal . Regular monitoring can warn operators of issues before they impact on the wider treatment process.

Primary and Secondary Clarification Are Not the Same

A useful distinction in wastewater clarification is the difference between primary and secondary clarification.

In most cases, primary clarification occurs prior to biological treatment. The aim is to eliminate settleable and floatable particles lowering the solids and organic load that the biological stage has to deal with. When properly designed, primary clarifiers may remove a large fraction of the suspended solids in the influent.

Following biological treatment, secondary clarifying is performed. At this stage the wastewater comprises biological solids generated in operations such as activated sludge treatment. The secondary clarifier separates the solids from the treated water . Some of the sludge may be returned to the biological process .

Some plants may need to use tertiary clarifying or other sophisticated treatment methods for extra contamination removal.

Why Clarifier Design Matters

Each treatment facility has different hydraulic conditions, footprint, flow rate and properties of wastewater. The equipment should be chosen to suit the facility, not just the capacity of the tanks.

Treatment facilities can be constructed in circular or rectangular layouts, and the flow pattern will dictate the path of the wastewater through the settling area. For example, the peripheral-feed designs deliver wastewater into the tank along the periphery and into the settling zone. This strategy aims at reducing hydraulic difficulties like short-circuiting and improving the use of the available settling volume.

When evaluating a clarifier wastewater treatment solution, a facility should examine the available space, influent characteristics, hydraulic loads, sludge removal requirements and maintenance access.

What Can Affect Clarifier Performance?

Even properly designed equipment can struggle when operating conditions change.

Common concerns include:

  • Excessive sludge accumulation
  • Sudden changes in wastewater flow
  • Poor settling characteristics
  • Mechanical wear
  • Corrosion
  • Improper sludge removal
  • Excessive surface scum

Operators can detect changes in performance by data such as total suspended solids, turbidity, sludge depth, flow conditions and equipment torque. For example, an increase in torque may imply greater mechanical resistance or strain from sludge.

That’s why regular inspections are important; an issue with a clarifier can eventually impact the treatment stages that follow it.

FAQs

Does every wastewater treatment plant use the same type of clarifier?

No, Treatment facilities vary in flow, footprint, effluent properties and treatment aims. Thus the clarifier configuration and sludge removal procedures may differ from one plant to another.

What is the main difference between primary and secondary clarification?

Primary clarification is normally used ahead of biological treatment to remove settleable and floatable materials. Further clarification clarifies the separation of biological solids after the biological treatment stage.

Can a clarifier remove every contaminant from wastewater?

No, Clarifiers are mainly used for solids separation. At later phases, biological treatment, filtration, chemical treatment or disinfection may be needed for dissolved contaminants, pathogens, nutrients and other pollutants.

The Bigger Role of a Clarifier

 A wastewater clarifier has a fairly straightforward physical job, but that job has implications throughout the treatment facility. Clarification is used to separate settleable solids, floating material and biological solids at the proper stage in the process to prepare wastewater for subsequent treatment procedures.

Its performance depends on more than just the tank. Proper separation is dependent on hydraulic design, sludge handling, operating conditions, mechanical parts and frequent maintenance. This knowledge provides treatment plant operators and planners with a stronger basis for evaluating clarity equipment and ensuring dependable treatment performance. 

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