Wastewater Treatment Basics

Wastewater treatment is a field that is extremely diverse and complex. Dr. Shashi Dubey, professor of civil and environmental engineering at Florida Atlantic University (FAU) offers insight into some of the basics of wastewater treatment. some of the basics terms and definitions are given below:

SVI or Sludge Volume Index

The Sludge Volume Index is a laboratory column setting test that measures the settling ability and compatibility of sludge.


The volume occupied by 1 gram of sludge after it has settled for a set period of time is known as the sludge volume index. The volume in millimeters occupied by 1 gram of sludge after it has settled for 20 minutes to 1 or 2 hours is referred to as the sludge volume index. 30 minutes is usually the settling duration allowed

  • The sludge settle ability is Excellent if SVI is 50 – 150ml/mg.

Activated Sludge System:

  1. Activated sludge from the final setting tanks’ underflow should be re-introduced to the aeration tank inlet at a rate that keeps the MLSS concentration at the desired level.
  2. The return-sludge flow rate and the sludge concentration at which it is extracted from the final setting tanks are both necessary for determining the needed flow.

As a result, only a simple measure of the underflow concentration is required from the settling tanks. The sludge volume index, SVI, which is 4 the amount of sludge occupied by 1.0g of sludge soiled (dry weight) after 30 minutes set up and has ht units ml/g was formerly used for this purpose. i.e., The sludge density index is sometimes represented as SDI.

The required rate of activated sludge return may be determined once the SVI and operating MLSS concentration (x) are known.

100 / [ 106/ (x) (SVI) -1] = r

The term r = return sludge flow rate represented as a % age of incoming sewage flow.


The process of removing solid particles from a suspension by sedimentation under gravity is known as flocculation.

The primary settling tanks in the treatment process help to remove sand, grit, and large floating objects. As a result, it is important that this part of the system works properly because effective secondary sedimentation will not take place without the proper removal of these particles.


When the organic matter is removed, the water will be separated from suspended solids. R = return sludge flow rate (ML/D) for Q in ML/D) is the ratio of water to suspended solids, where R = separation of water from Suspended Solids.


A strainer is a type of sieve that is used to separate particles. A mesh, for example, will keep larger objects like plant roots from clogging the intake hose. It’s also the same word that refers to the role of an extraction mechanism in sedimentation.


Variations involved in The Activated Sludge Process:

  • The activated sludge technique was developed in 1941 and has gone through several modifications and adaptations.
  • Many modifications have sought to increase the plug flow activated sludge plant’s loading capacity by providing optimum condition design specifications for different forms of plants are outlined in tableIt’s important to note that five modifications taper aeration is a key aspect of the CMAS process, and all pure oxygen systems and deep shaft processes strive toward improved oxygen transfer efficiency and more efficient distribution of available oxygen to match demand.The method of operation, however, is significantly different. -> The process is comparable to that of CAS (Conventional Activated Sludge), with the exception that it uses biological treatment rather than chemical treatment.


  • Volumetric loading = kg of BOD


  • Aerial loading rate = gm of BOD


Where the Td = V/Q in a unit of days and is usually greater than 5 days.


Algal-bacterial symbiosis is a term that refers to the association of algae and bacteria during this process.

  1. Shock loading (CSTR)
  2. BODu

Sludge Treatment:

Anaerobic sludge treatment cell The Primary Sedimentation Tank and Secondary Sedimentation tanks are made of organic materials, which may be treated aerobically.

  1. Treatment of sewage water in anaerobic ponds and septic tanks is required.
  2. Anaerobic sludge treatment is a type of sewage treatment.

Aerated Lagoons:

Aerate lagoons are wastewater treatment plants without sludge return that use activated sludge. In the past, they were created from waste stabilization ponds in temperate zones where mechanical aeration was used to supplement the algal oxygen supply during the winter season.

The algal disappeared after the aeration was turned on, and the microflora returned to normal. Activated sludge units were now generally designed as fully mixed not-return systems rather than aerated lagoons.

The most popular way to add air and mixing power to a pool is with a floating aerator.

Sludge Treatment Process Terms :

SLUDGE: The fine impurities settled at the bottom of the flower bed of sedimentation tanks.


To break down or decay as a result of heat, moisture, or chemical action.

Sludge treatment:

The process of converting organic waste material to mean and inure CO2, without the presence of oxygen, is known as aerobic digestion.

Organic matter + H2O (amoebas) = CH4+ CO2 + NH3+ H2S + heat

Anaerobic digestion has several advantages. Anabolic detectors are divided into two categories. It’s made up of two types:

  1. The number of stages varies from one to four in a high-tech (stranded) or low-rate digester, and from two to seven in a cold digester.
  2. The most popular digesters are continuous miring except for when sludge is being drawn, and high-rate digesters have two-stage digesters.

Wastewater Treatment Conclusion:

The activated sludge treatment process consists of biological washing and aeration. In this process, both aerobic and anaerobic bacteria are used to remove pollutants from wastewater. The design of a plant may vary depending on the industrial sector, but all plants have a primary sedimentation tank and a secondary settlement tank in common.

And it is also true that processes such as clarifiers, tanks, filters, etc., have their own terms that need to be understood before they can be applied properly.

In conclusion, the sludge treatment is made up of two types: aerobic digestion and anaerobic digestion. In this process, both aerobic and anaerobic bacteria work together to treat wastewater at different stages.

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