The activated sludge process of sewage treatment is based on providing intimate contact between the sewage and activated sludge. The activated sludge is the sludge which is obtained by settling sewage in presence of abundant oxygen so as to be enriched with aerobic micro-organisms.
What is the purpose of Return Activated Sludge?
Process description
- Bioreactor and final clarifier. ...
- Sludge production. ...
- Process control. ...
- Package plants. ...
- Oxidation ditch. ...
- Deep shaft / Vertical treatment. ...
- Surface-aerated basins. ...
- Sequencing batch reactors (SBRs) Sequencing batch reactors (SBRs) treat wastewater in batches within the same vessel. ...
What is returned activated sludge?
return activated sludge (RAS) Settled activated sludge that is collected in the secondary clarifier or the membrane basin and returned to the aeration basin to mix with incoming raw or primary settled wastewater.
What is conventional activated sludge process?
Conventional Activated Sludge (CAS)
- Low installation cost (Cost effective)
- Good quality effluent
- Small land area requirement
- Loss of head is small
- Freedom from fly and odor nuisance high degree of treatment
- Easily maintained mechanical work
- Self-sustaining system Activated Sludge Principles
- Wastewater is aerated in a tank
- Bacteria are encouraged to grow by providing
- Oxygen
How does activated sludge work?
- The amount of undesired sludge is reduced.
- The sewage treatment plants re-seed themselves with beneficial bacteria.
- The activated sludge treatment process allows the emptying intervals to be longer.
- The process is very reliable.
- The process is more simple.
- Costs are reduced.
- The process can be odorless.
How is an activated sludge formed?
(a) As the BOD of sewage or waste water is reduced to about 10-15%, the effluent is passed into a settling tank where the bacterial flocs undergo sedimentation. The sediment is called activated sludge.
How is sewage sludge produced?
Primary sludge is generated from chemical precipitation, sedimentation, and other primary processes, whereas secondary sludge is the activated waste biomass resulting from biological treatments. Some sewage plants also receive septage or septic tank solids from household on-site wastewater treatment systems.
What is activated sludge and how is it made?
The activated sludge process is a means of treating both municipal and industrial wastewater. The activated sludge process is a multi-chamber reactor unit that uses highly concentrated microorganisms to degrade organics and remove nutrients from wastewater, producing quality effluent.
What is meant by activated sludge?
The activated sludge is a process with high concentration of microorganisms, basically bacteria, protozoa and fungi, which are present as loose clumped mass of fine particles that are kept in suspension by stirring, with the aim of removing organic matter from wastewater.
What are the 4 steps of sewage treatment?
4-Step Wastewater Sludge Treatment ProcessStep 1 – Sludge Thickening. The first step in the sewage sludge treatment plan is called thickening. ... Step 2 – Sludge Digestion. After amassing all the solids from the sewage sludge begins the sludge digestion process. ... Step 3 – Dewatering. ... Step 4 – Disposal.
What is sewage sludge made of?
Sewage sludge is produced from the treatment of wastewater in sewage treatment plants and consists of two basic forms — raw primary sludge and secondary sludge, also known as activated sludge in the case of the activated sludge process.
What type of fluid is sewage sludge?
It is known that suspensions of biological sewage sludge are non-Newtonian fluids [9]. However, from the rheological point of view very thin layers behave as Newtonian fluid. When the suspension is concentrated the sludge starts to behave as non-Newtonian fluid [6].
How much sewage sludge is produced?
Processed municipal sewage sludge (MSS) or biosolids are an abundant byproduct of wastewater treatment. About 6.5 million metric dry tonnes (7.18 million U.S. tons) of MSS is produced in the U.S. annually (NEBRA 2007).
What is septic sludge made of?
Sludge: Sludge is the solid material that settles at the bottom of your septic tank to form a thick layer. The sludge is made up of non-liquid materials like soil, bones, food particles, etc. There are anaerobic bacteria that thrive in the bottom of your tank that feed off of this sludge layer.
What is activated sludge?
The activated sludge is the sludge which is obtained by settling sewage in presence of abundant oxygen so as to be enriched with aero bic micro-organisms.
When was activated sludge developed?
The activated sludge process was developed in England in 1914 by Ardern and Lockett and was so named because it involved the production of an activated mass of micro-organisms capable of aerobically stabilizing a waste.
How long does it take for activated sludge to form?
Hence, when a new plant is put in operation, a period of about 4 weeks is required to form a suitable activated sludge, and during this period almost all the sludge from the secondary settling tank will be returned through the aeration tank.
Why is secondary settling important?
Secondary settling assumes considerable importance in the activated sludge process as the efficient separation of the biological sludge is necessary not only for ensuring final effluent quality but also for return of adequate sludge to maintain the MLSS level in the aeration tank.
How much of activated sludge is returned?
In the activated sludge process either raw sewage or the effluent from the primary settling tank is mixed with 20 to 50 percent of its own volume of returned activated sludge. The mixture enters an aeration tank where the organisms and sewage are mixed together with a large quantity of air.
Why is oxygen needed in activated sludge?
Oxygen is required in the activated sludge process for the oxidation of a part of the influent organic matter and also for the endogenous respiration of the micro-organisms in the system. The former is a function of BOD removal, while the latter is a function of MLVSS in the aeration tank.
What is the concentration of suspended solids in activated sludge?
The suspended-solids concentration maintained in the mixed liquor (MLSS) of a conventional activated sludge process ranges from 1000 to 4000 mg/l. The concentration of volatile suspended solids (VSS) in the mixed liquor is usually 60 to 85 percent of the total suspended solids.
What is activated sludge?
Activated sludge is also the name given to the active biological material produced by activated sludge plants. Excess sludge is called "surplus activated sludge" or "waste activated sludge" and is removed from the treatment process to keep the ratio of biomass to food supplied in the wastewater in balance. This sewage sludge is usually mixed with primary sludge from the primary clarifiers and undergoes further sludge treatment for example by anaerobic digestion, followed by thickening, dewatering, composting and land application.
What is the mechanism of mixing sewage and sludge?
As the sewage rises the oxygen forced into solution by the pressure at the base of the shaft breaks out as molecular oxygen providing a highly efficient source of oxygen for the activated sludge biota. The rising oxygen and injected return sludge provide the physical mechanism for mixing of the sewage and sludge.
What is pure oxygen sludge aeration?
Pure oxygen activated sludge aeration systems are sealed-tank reactor vessels with surface aerator type impellers mounted within the tanks at the oxygen carbon liquor surface interface . The amount of oxygen entrainment, or DO (Dissolved Oxygen), can be controlled by a weir adjusted level control, and a vent gas oxygen controlled oxygen feed valve. Oxygen is generated on site by cryogenic distillation of air, pressure swing adsorption, or other methods. These systems are used where wastewater plant space is at a premium and high sewage throughput is required as high energy costs are involved in purifying oxygen.
How to reduce space in sewage treatment plant?
The space required for a sewage treatment plant can be reduced by using a membrane bioreactor to remove some wastewater from the mixed liquor prior to treatment. This results in a more concentrated waste product that can then be treated using the activated sludge process.
What is brown floc?
This material, which in healthy sludge is a brown floc , is largely composed of Saprotrophic bacteria but also has an important protozoan flora component mainly composed of amoebae, Spirotrichs, Peritrichs including Vorticellids and a range of other filter-feeding species.
How is sewage treated in a short supply area?
Where land is in short supply sewage may be treated by injection of oxygen into a pressured return sludge stream which is injected into the base of a deep columnar tank buried in the ground. Such shafts may be up to 100 metres deep and are filled with sewage liquor.
How often is sludge blanket measured in a reactor?
In the reactor/aerator and clarifier system, the sludge blanket is measured from the bottom of the clarifier to the level of settled solids in the clarifier's water column; this, in large plants, can be done up to three times a day.
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