BIOLOGICAL WASTEWATER TREATMENT WITH ACTIVATED-SLUDGE PROCESS – In a simplified flow diagram for biological processes used for wastewater treatment, the influent wastewater (e.g. municipal wastewater) goes through several stages in which different compound are removed out of the wastewater. In the Bar Rack coarse solids are removed, such as sticks, rags, and other debris in untreated wastewater by interception. By use of fine screening even floatable matter and algae are removed. In the Grit Chamber grit is removed consisting of sand, gravel, cinders, or other heavy solid materials that have subsiding velocities or specific gravities substantially greater than those of the organic putrescible solids in wastewater. The Primary Clarifier is a basin where water has a certain retention time where the heavy organic solids can sediment (suspended solids). Efficiently designed and operated primary sedimentation tanks should remove from 50 to 70 percent of the suspended solids and 25 to 40 percent of the BOD. The influent of the aeration tank is mixed with activated sludge and in the Aeration Tank the mixed liquor is aerated. By aerating the mixed liquor the aerobic processes will be stimulated, the growth rate of bacteria will be must faster. Because the bacteria deplete the substrate, flocculation takes place. The soluble substrate becomes a solid biomass. These flocks of biomass will sediment in the Secondary Clarifier. At the end of the process the effluent water is treated to Disinfect it and make it free of disease-causing organisms. Lenntech provides innovative and sustainable solutions for water treatment and liquid separation, focusing on industrial applications.

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Biological Wastewater Treatment with Activated-Sludge Process

Lenntech Water Treatment Solutions

 

The picture below shows a simplified flow diagram for biological processes used for wastewater treatment.

The influent wastewater (e.g. municipal wastewater) goes through several stages in which different compound are removed out of the wastewater.

For more information about the process, please click on one of the process stages.

Simplified flow diagram for a biological wastewater treatment with a activated-sludge process.

In the Bar Rack coarse solids are removed, such as sticks, rags, and other debris in untreated wastewater by interception.

By use of fine screening even floatable matter and algae are removed. (p. 314)

In the Grit Chamber grit is removed consisting of sand, gravel, cinders, or other heavy solid materials that have subsiding velocities or specific gravities substantially greater than those of the organic putrescible solids in wastewater. (p. 384)

The Primary Clarifier is a basin where water has a certain retention time where the heavy organic solids can sediment (suspended solids). (p.384)

Efficiently designed and operated primary sedimentation tanks should remove from 50 to 70 percent of the suspended solids and 25 to 40 percent of the BOD. (p.396)

The influent of the aeration tank is mixed with activated sludge and in the Aeration Tank the mixed liquor is aerated.

By aerating the mixed liquor the aerobic processes will be stimulated, the growth rate of bacteria will be must faster.

Because the bacteria deplete the substrate, flocculation takes place.

The soluble substrate becomes a solid biomass. These flocks of biomass will sediment in the Secondary Clarifier.

At the end of the process the effluent water is treated to Disinfect it and make it free of disease-causing organisms.

Lenntech Water Treatment Solutions, established in 1993, is a design and manufacturing company situated in The Netherlands, near the Technical University of Delft.
Lenntech provides innovative and sustainable solutions for water treatment and liquid separation, focusing on industrial applications. With an experienced team of sales, environmental, chemical, mechanical and electrical engineers we are specialized in providing turnkey and customized water purification and membrane separation systems for numerous different industries and applications.
Our wide range of technologies and extended know-how in all water-related sectors will guarantee you a cost-efficient solution that will meet your water quality requirements. Each water and liquid stream are unique, and we prioritize research and development to keep our solutions and products in the front line.
https://www.lenntech.com/wwtp/wwtp-overview.htm

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CENTRIFUGATION - Understanding the forces that pull rotating objects outward - The term centrifuge can refer to a machine that houses a rapidly rotating container to separate its contents by density (noun) or to the act of using the machine (verb). Centrifuges are most often used to separate different liquids and solid particulates from liquids, but they may be used for gases. They are also used for purposes other than mechanical separation. A centrifuge gets its name from centrifugal force — the virtual force that pulls spinning objects outward. Centripetal force is the real physical force at work, pulling spinning objects inward. Spinning a bucket of water is a good example of these forces at work. If the bucket spins fast enough, the water is pulled inward and doesn't spill. If the bucket is filled with a mixture of sand and water, spinning it produces centrifugation. According to the sedimentation principle, both the water and sand in the bucket will be drawn to the outer edge of the bucket, but the dense sand particles will settle to the bottom, while the lighter water molecules will be displaced toward the center. The centripetal acceleration essentially simulates higher gravity, however, it's important to keep in mind the artificial gravity is a range of values, depending on how close an object is to the axis of rotation, not a constant value. The effect is greater the further out an object gets because it travels a greater distance for each rotation. The types of centrifuges are all based on the same technique but differ in their applications. The main differences between them are the speed of rotation and the rotor design.

 

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Centrifugation

What It is and Why It's Used

Understanding the forces that pull rotating objects outward

By Anne Marie Helmenstine, Ph.D.

The term centrifuge can refer to a machine that houses a rapidly rotating container to separate its contents by density (noun) or to the act of using the machine (verb).

Centrifuges are most often used to separate different liquids and solid particulates from liquids, but they may be used for gases.

They are also used for purposes other than mechanical separation.

Invention and Early History of the Centrifuge

The modern centrifuge traces its origins to a spinning arm apparatus designed in the 18th century by English military engineer Benjamin Robins to determine drag.

In 1864, Antonin Prandtl applied the technique to separate the components of milk and cream.

In 1875, Prandtl's brother Alexender, refined the technique, inventing a machine to extract butterfat.

While centrifuges are still used to separate milk components, their use has expanded to many other areas of science and medicine.

How a Centrifuge Works

A centrifuge gets its name from centrifugal force — the virtual force that pulls spinning objects outward. 

Centripetal force is the real physical force at work, pulling spinning objects inward. Spinning a bucket of water is a good example of these forces at work.

If the bucket spins fast enough, the water is pulled inward and doesn't spill.

If the bucket is filled with a mixture of sand and water, spinning it produces centrifugation.

According to the sedimentation principle, both the water and sand in the bucket will be drawn to the outer edge of the bucket, but the dense sand particles will settle to the bottom, while the lighter water molecules will be displaced toward the center.

The centripetal acceleration essentially simulates higher gravity, however, it's important to keep in mind the artificial gravity is a range of values, depending on how close an object is to the axis of rotation, not a constant value.

The effect is greater the further out an object gets because it travels a greater distance for each rotation.

Types and Uses of Centrifuges

The types of centrifuges are all based on the same technique but differ in their applications.

The main differences between them are the speed of rotation and the rotor design. The rotor is the rotating unit in the device.

Fixed-angle rotors hold samples at a constant angle, swinging head rotors have a hinge that allows sample vessels to swing outward as the rate of spin increases, and continuous tubular centrifuges have a single chamber rather than individual sample chambers.

Separating Molecules and Isotopes: Extremely high-speed centrifuges and ultracentrifuges spin at such high rates that they can be used to separate molecules of different masses or even isotopes of atoms.

Isotope separation is used for scientific research and to make nuclear fuel and nuclear weapons.

For example, a gas centrifuge may be used to enrich uranium, as the heavier isotope is pulled outward more than the lighter one.

In the Lab: Laboratory centrifuges also spin at high rates. They may be large enough to stand on a floor or small enough to rest on a counter. 

A typical device has a rotor with angled drilled holes to hold sample tubes.

Because the sample tubes are fixed at an angle and centrifugal force acts in the horizontal plane, particles move a tiny distance before hitting the wall of the tube, allowing dense material to slide down.

While many lab centrifuges have fixed-angle rotors, swinging-bucket rotors are also common. 

Such machines are employed to isolate components of immiscible liquids and suspensions. Uses include separating blood components, isolating DNA, and purifying chemical samples.

High-Gravity Simulation: Large centrifuges may be used to simulate high-gravity. The machines are the size of a room or building.

Human centrifuges are used to train test pilots and conduct gravity-related scientific research.

Centrifuges may also be used as amusement park rides.

While human centrifuges are designed to go up to 10 or 12 gravities, large-diameter non-human machines can expose specimens to up to 20 times normal gravity. 

The same principle may one day be used to simulate gravity in space. 

Industrial Centrifuges are used to separate components of colloids (like cream and butter from milk), in chemical preparation, cleaning solids from drilling fluid, drying materials, and water treatment to remove sludge.

Some industrial centrifuges rely on sedimentation for separation, while others separate matter using a screen or filter.

Industrial centrifuges are used to cast metals and prepare chemicals.

The differential gravity affects the phase composition and other properties of the materials.

Everyday Applications: Medium-size centrifuges are common in daily life, mainly to quickly separate liquids from solids.

Washing machines use centrifugation during the spin cycle to separate water from laundry.

A similar device spins the water out of swimsuits.

Salad spinners, used to wash and then spin dry lettuce and other greens, are another example of a simple centrifuge.

Related Techniques

While centrifugation is the best option for simulating high gravity, there are other techniques that may be used to separate materials.

These include filtration, sieving, distillation, decantation, and chromatography.

The best technique for an application depends on the properties of the sample being used and its volume.

Anne Marie Helmenstine, Ph.D.

Chemistry Expert

Education

Ph.D., Biomedical Sciences, University of Tennessee at Knoxville

B.A., Physics and Mathematics, Hastings College

Introduction

Ph.D. in biomedical sciences from the University of Tennessee at Knoxville - Oak Ridge National Laboratory.

Science educator with experience teaching chemistry, biology, astronomy, and physics at the high school, college, and graduate levels.

ThoughtCo and About Education chemistry expert since 2001.

Widely-published graphic artist, responsible for printable periodic tables and other illustrations used in science.

Experience

Anne Helmenstine, Ph.D. has covered chemistry for ThoughtCo and About Education since 2001, and other sciences since 2013. She taught chemistry, biology, astronomy, and physics at the high school, college, and graduate levels. She has worked as a research scientist and also abstracting and indexing diverse scientific literature for the Department of Energy.

In addition to her work as a science writer, Dr. Helmenstine currently serves as a scientific consultant, specializing in problems requiring an interdisciplinary approach. Previously, she worked as a research scientist and college professor. 

Education

Dr. Helmenstine holds a Ph.D. in biomedical sciences from the University of Tennessee at Knoxville and a B.A. in physics and mathematics with a minor in chemistry from Hastings College. In her doctoral work, Dr. Helmenstine developed ultra-sensitive chemical detection and medical diagnostic tests.

ThoughtCo and Dotdash

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https://www.thoughtco.com/centrifuge-definition-4145360

DEFINITIONS IN WASTE WATER TREATMENT - Sludge Volume Index (SVI-TEST) is the measure of the settleability and compatibility of sludge and is made from a laboratory column setting test. The sludge volume index is the volume in mm occupied by 1 gm of sludge after it has settled for a specified period of time’ generally ranging from 20 min to 1 or 2 hr in a 1 – or 2-l cylinder. The activated sludge forms the underflow of the final setting tanks should be returned to the inlet of the aeration tanks at a rate sufficient to maintain the MLSS concentration at the design value. The flow are needed for return-sludge is determined form the incoming sewage flow rate and the concentration at which the sludge is withdrawn form the final setting tanks. SEDIMENTATION is the removal of solid particles form a suspension by settling under gravity. CLARIFICATION is a similar term which refers specifically to the function of a sedimentation removal. THICKENING means the separation of water from suspended solids.

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Definitions in Waste Water Treatment

By: Haseeb Jamal 

Sludge Volume Index (SVI-TEST)

It is the measure of the settleability and compatibility of sludge and is made from a laboratory column setting test.

Definition

The sludge volume index is defined as ‘the volume in mm occupied by 1 gm of sludge after it has settled for a specified period of time’ generally ranging from 20 min to 1 or 2 hr in a 1 – or 2-l cylinder.

One-half hour is most common setting time allowed to the mixed liquor to settle for 30 min. (larger cylinder is desirable to minimize bridging of sludge floe and war effects).

Take the reading let Vs is the settled volume of sludge (ml/l) in 30 min.

* If SVI is 50 - 150 ml/mg, the sludge settle ability is Good.

Return Activated Sludge System:

1.The activated sludge forms the underflow of the final setting tanks should be returned to the inlet of the aeration tanks at a rate sufficient to maintain the MLSS concentration at the design value.

2.The flow are needed for return-sludge is determined form the incoming sewage flow rate and the concentration at which the sludge is withdrawn form the final setting tanks.

Hence a simple measure of the underflow concentration forms the setting tanks is required.

The parameter conventionally employed for this purpose the sludge volume index, SVI which is defined as 4 the volume occupied by sludge containing 1.0g of sludge soiled (dry weight) after 30 min setting and thus it has ht units ml/g.

Sometimes represented as SDI i.e sludge density index. Once the SVI and operating MLSS concentration (x) is known, the required rate of activated sludge return can be determined

R = 100 / [ 106/ (x) (SVI) -1] where r = return sludge flow rate as a % age of incoming sewage flow.

SEDIMENTATION:

It is the removal of solid particles form a suspension by settling under gravity.

CLARIFICATION:

It is a similar term which refers specifically to the function of a sedimentation removal.

THICKENING:

It means the separation of water from Suspended Solids where R = return sludge flow rate (ML/D) for Q in ML/D)

SURFACE GEOMETRY OF FINAL SEDIMENTATION TANKS:

VARIATION OF THE ACTIVATED SLUDGE PROCESS:

1.  Activated sludge was introduced in 1941 and has undergone many variations and adaptations.

2.  The main objective of many modifications has been to increase the loading capacity of the basic plug flow activated sludge plant by provision of optimum condition design parameters for different variations are summarized in table.

It is worthy of note that 5 modifications tapered aeration step aeration the CMAS process, the pure oxygen system and the deep shaft process all aim at either the improvement of oxygen transfer efficiency t the efficient distribution of available oxygen to match demand.

A flow sheet of most of the commonly used variations is similar to that of CAS (Conventional Activated Sludge).

CONVENTIONAL ACTIVATED SLUDGE:

Volumetric loading = kg of BOD
                                      m³-d
Aerial loading rate = gm of BOD
                                      m³-d
Td = V/Q in days and greater than 5 days.

ALGAL-BACTERIAL SYMBIOSIS:

The combined and mutually- been facial action of algae and bacteria in this process is called algal-bacterial symbioses.

·            Shock loading (CSTR)

·            BODu

Aerated Lagoons:

Aerate lagoons are activated sludge units operated without sludge return.

Historically they were developed from waste stabilization ponds in temperate climate where mechanical aeration was used to supplement the algal oxygen supply in winter.

It was found, however that soon after the aerations were put into operation the algal disappeared and the microbial flora resembled that of activated sludge.

Aerated lagoons were now usually design as completely mixed not-return activated sludge units.

Floating aerates are most commonly used to supply the necessary oxygen and mixing power.

Sludge Treatment:

Anaerobic sludge treatment cell Primary Sedimentation Tank and Secondary Sedimentation Tank are basically organic these can be treated to aerobic.

·      Anaerobic ponds and septic tank are for waste water treatment.

·      Sludge treatment = Anaerobic sludge treatment.

COLD DIGESTION:

·         Two stage digestion up

·         High rate digestion up

·         Fixed film processes. A swm zone

SLUDGE DIGESTION:

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

Digestion:

To decompose or breakdown by heat and moisture or chemical action. (to invent food equable forms)

Sludge treatment:

Anaerobic digestion it is defined as ‘it is the use of microbial organisms in the absence of oxygen for the stabilization of oxygen materials by conversion to mean and inure produce including CO₂.

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

Benefices of anaerobic digestion. Types of anabolic detectors. It’s of two types:

·      Conventional (stranded) or low-rate digester or cold digester.

·      High rate digesters / two stage digester are characterized by continuous miring except at time of sludge with draw.

Haseeb Jamal. I am a Civil Engineer, graduated from University of Engineering and Technology, Peshawar, Pakistan in 2010. I also have a PG-Diploma in Disaster Management and MS in Urban Infrastructure Engineering (In Progress). My expertise include civil related softwares like AutoCAD, SAP2000, MS Project, Primavera, MS Office and GIS. My technical skills include project management, monitoring and evaluation, structural assessment, disaster risk management, Quantity survey, land survey, material testing, site management and technical writing. I am trained in writing project progress reports as well as proposals and concept papers. I have also received advanced training on surveying, proposal writing, Monitoring and Evaluation of projects as well as organizations.I have worked as Project Engineer at National Research and Development Foundation, Peshawar and CENCON Associates. I also worked with Spectra Engineering Solutions as Senior Civil Engineer in monitoring of World Bank and UNDP funded projects all over Khyber Pakhtunkhwa and FATA. Currently, I am working as Deputy Manager Development at NayaTel, Peshawar.

https://www.aboutcivil.org/waste-water-technical-terms-definitions