Settling process in wastewater treatment
Settling process in wastewater treatment

The settling process is an important stage in wastewater treatment that involves the removal of suspended solids and other impurities from the water. In this process, the wastewater is allowed to sit in a tank or basin for a period of time to allow the heavier solids to settle to the bottom, while the lighter particles and organic matter remain in the upper layer of the water. Settling process, also known as sedimentation, is a common and essential step in wastewater treatment. It is a physical treatment process that separates solid particles from wastewater by gravity settling. During the settling process, wastewater is allowed to flow slowly through a sedimentation tank or clarifier. The velocity of the flow is reduced, which causes the solid particles to settle to the bottom of the tank due to gravity. The settled solids are called sludge, and the clear water above it is called supernatant. The supernatant is then discharged for further treatment or discharged into the environment.

 

1. Working Principle


The settling process in wastewater treatment works on the principle of gravity separation. The wastewater flows into a settling tank or clarifier, which is designed to slow down the velocity of the flow. As the velocity slows down, the solid particles in the wastewater start to settle to the bottom of the tank due to gravity.


The settled particles form a layer of sludge at the bottom of the tank, while the clear water above it, called supernatant, is discharged for further treatment or discharge into the environment.

The settling process can be enhanced by the addition of chemicals such as coagulants and flocculants. Coagulants cause the smaller particles to clump together and form larger particles, called flocs. Flocculants help to make the flocs heavier, which increases the settling rate.


The settling process is designed to have an optimum detention time to allow the particles to settle fully. The detention time is the time that the wastewater spends in the settling tank, and it is determined by the design of the tank and the flow rate of the wastewater. After settling, the sludge at the bottom of the tank can be removed and further treated for solids reduction and stabilization before disposal or reuse. It relies on gravity to separate solid particles from wastewater and is an important step in wastewater treatment to remove suspended solids and protect the environment and public health.


2. Types of settling process:


There are several types of settling processes used in wastewater treatment. These include:


2.1.  Gravity Settling: This is the most common type of settling process and involves allowing the wastewater to flow slowly through a sedimentation tank or clarifier. The velocity of the flow is reduced, which causes the solid particles to settle to the bottom of the tank due to gravity.


2.2.  Upflow Sludge Blanket Clarifier (USBC): This process involves the use of a sludge blanket to separate the solids from the wastewater. The wastewater flows upward through the sludge blanket, and the solid particles are captured and settle to the bottom of the tank.

 

2.3.  Inclined Plate Settlers: In this process, the wastewater flows through a series of inclined plates. The plates have a large surface area, which causes the solid particles to settle on the plates due to gravity. The settled solids are then removed from the plates.


2.4.  Dissolved Air Flotation (DAF): This process involves the use of tiny air bubbles to attach to the solid particles, making them lighter and allowing them to float to the surface of the tank. The floating solids are then skimmed off the surface.


2.5.  Biological Settling: This process is used in activated sludge systems and involves the use of microorganisms to break down organic matter in the wastewater. The microorganisms form flocs, which settle to the bottom of the tank.

         


3. Application Industries:


Settling processes are used in various industries to treat wastewater and remove suspended solids. Some of the industries that commonly use settling processes in wastewater treatment include:


·      Municipal Wastewater Treatment: Settling processes are commonly used in municipal

wastewater treatment to remove suspended solids, organic matter, and nutrients from

wastewater before it is discharged into the environment.

·      Food and Beverage Processing: The food and beverage industry produces large volumes of

wastewater containing organic matter, suspended solids, and other contaminants. Settling

processes can be used to treat this wastewater and remove the contaminants prior discharge.

·      Chemical and Petrochemical Industry: The chemical and petrochemical industry produces

wastewater containing a range of contaminants, including suspended solids, organic matter,

and heavy metals. Settling processes can be used to treat this wastewater and remove the

contaminants.

·      Mining Industry: The mining industry generates wastewater containing suspended solids,

metals, and other contaminants. Settling processes can be used to treat this wastewater and

remove the contaminants before discharge.

·      Pulp and Paper Industry: The pulp and paper industry generates wastewater containing

suspended solids, organic matter, and other contaminants. Settling processes can be used to

treat this wastewater and remove the contaminants before discharge.



4. Advancement Technologies:

There have been significant advances in water treatment technologies in recent years, aimed at providing access to clean and safe drinking water, reducing water pollution, and promoting sustainable water management. Some of the advanced technologies in wastewater treatment include:

·      Membrane Bioreactors (MBRs): MBRs combine biological treatment with membrane filtration to produce high-quality effluent. The membranes used in MBRs are fine enough to filter out bacteria, viruses, and other contaminants, making them ideal for treating wastewater for reuse.

 

·      Moving Bed Biofilm Reactors (MBBRs): MBBRs use a fixed-film biological treatment process in which bacteria grow on plastic media that is suspended in the wastewater. The bacteria break down organic matter and nutrients, producing a high-quality effluent that can be discharged into the environment or reused for irrigation or other non-potable purposes.

·      Reverse Osmosis (RO): RO is a membrane filtration process that uses pressure to force water through a semipermeable membrane. The membrane allows water molecules to pass through, while rejecting larger molecules and contaminants, such as salts and organic matter. RO is often used as a final polishing step in wastewater treatment to produce high-quality effluent for reuse.

        

 

·      Ultraviolet (UV) Disinfection: UV disinfection uses ultraviolet light to destroy bacteria, viruses, and other pathogens in wastewater. UV disinfection is a chemical-free process that is effective against a wide range of microorganisms and is often used as a final step in wastewater treatment to ensure that the effluent is safe for discharge into the environment.

 

             

·      Electrocoagulation (EC): EC is an emerging wastewater treatment technology that uses an electric current to coagulate, and flocculate suspended particles, making them easier to remove from the water. EC can be used as a primary treatment step or as a polishing step after biological treatment to remove residual pollutants.

                      

 

5.    Reference:

·      https://en.wikipedia.org/wiki/Wastewater_treatment

·      https://www.safewater.org/fact-sheets-1/2017/1/23/wastewater-treatment

·     https://organicabiotech.com/advanced-wastewater-management-technologies-for-reduction-of-pollutants-in wastewater/#:~:text=Membrane%20Bio%2DReactor%20Technology%20or,achieving%20superior%20wastewater%20treatment%20objectives.

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