The process of active sludge is a type of wastewater treatment process for industrial waste or wastewater treatment using aeration and biological floc which consists of bacteria and protozoa.
Video Activated sludge
Destination
In sewage treatment plants (or industrial wastewater), active sludge processes are biological processes that can be used for one or more of the following purposes: oxidize the biological matter of carbon, oxidize nitrogenous materials: mainly ammonium and nitrogen in biological matter, eliminate nutrients (nitrogen and phosphorus ).
Maps Activated sludge
Description of process
This process utilizes aerobic micro-organisms that can digest organic matter in waste, and collect together (with flocculation) as they do so. It thus produces relatively free liquids from suspended solids and organic materials, and flocculated particles that will easily precipitate and can be removed.
The general arrangements of active sludge processes to remove carbon pollution include the following:
- Aeration tank where air (or oxygen) is injected into the liquor mixture.
- The settling tank (commonly referred to as the "final clarifier" or "secondary deposition tank") to allow biological flocs to settle, thus separating the biological mud from clearly treated water.
Treatment of nitrogen or phosphate materials involves additional steps in which the mixed liquid is left in an anoxic condition (meaning no residual dissolved oxygen).
Bioreactor and end explorer
This process involves air or oxygen being fed into the filtered waste mixture, and primary treated waste or industrial wastewater (wastewater) combined with organisms to develop biological flocs that reduce the organic content of the waste. This material, which in healthy mud is brown floc, is largely composed of saprotrophic bacteria but also has an important protozoan flora component consisting mainly of amoebae, Spirotrichs, Peritrichs including Vorticellids and various other filter-eating species. Other important constituents include the bathed and settled Rotifers. In poorly managed sludge, various mucilaginous filamentous bacteria can develop including Sphaerotilus natans that produce mud that is difficult to precipitate and can produce a mud blanket soaking up the weir in the storage tank until it is severe. contaminate the quality of final waste. This material is often described as a mushroom waste but a true mushroom community is relatively rare.
The combination of wastewater and biological mass is commonly known as mixed liquor. In all active sludge factories, after the waste water has received adequate treatment, excessive excess beverages are discharged into the treated sedimentation tank and supernatant removed to undergo further treatment before disposal. Part of the finished material, mud, is returned to the head of the aeration system to reproduce the new wastewater entering the tank. The fraction of this floc is called return active sludge (R.A.S.).
The space required for a sewage treatment plant can be reduced by using a membrane bioreactor to remove some of the waste water from the liquor mixture before treatment. This produces a more concentrated waste product which can then be processed using an active sludge process.
Many sewage plants use axial flow pumps to transfer the nitrification liquor mixture from the aeration zone to the anoxic zone for denitrification. This pump is often referred to as the internal mixed drink recycle pump (IMLR pump). Raw wastewater, RAS, and liquor mixes are mixed with a submersible mixer in the anoxic zone to achieve denitrification.
Production of mud
Active sludge is also the name given to the biologically active substances produced by active sludge plants. Excess mud is called "activated sludge surplus" or "active sludge waste" and discharged from the treatment process to maintain the ratio of biomass to food provided in wastewater in equilibrium. This waste sludge is usually mixed with primary sludge from the main clarifiers and undergoes further mud treatment eg with anaerobic digestion, followed by thickening, dewatering, composting and land application.
The amount of sludge waste generated from the active sludge process is directly proportional to the amount of wastewater treated. Total mud production comprises the amount of primary sludge from the main sedimentation tank as well as the active sludge waste from the bioreactor. The active sludge process produces about 70-100 kg/mL of active sludge waste (ie kg of dry solids produced per ML from treated wastewater; one mega liter (ML) is 10 3 m 3 ). A value of 80 kg/ml is considered typical. In addition, about 110-170 kg/ml of primary mud is produced in main sedimentary tanks that are mostly - but not all - of the active sludge process configuration used.
The variant of the active sludge process is the Nereda process in which granular aerobic sludge is developed by applying specific process conditions that support slow-growing organisms.
Process control
The general process control method is to monitor the level of mud blankets, SVI (Mud Volume Index), MCRT (Mean Cell Left), F/M (Food for Microorganisms), as well as active sludge biota and DO (dissolved oxygen) nitrogen, phosphate, BOD (Biochemical oxygen demand), and COD (Chemical oxygen demand). In the reactor/aerator and clarifier system, the sludge blanket is measured from the bottom of the clarifier to the level of solids that settle in the water column of the clarifier; This, in large plants, can be done up to three times a day.
SVI is the volume of silt sludge in milliliters occupied by 1 gram of dry mud solids after 30 minutes of precipitation in a 1000 milliliter graduation cylinder. MCRT is the total mass (lbs) of the suspended solid mixture of liquor in the aerator and the clarifier divided by the mass flow rate (lbs/day) of the suspended liquid mixture leaving as WAS and final waste. The F/M is the ratio of food fed to microorganisms daily to the mass of microorganisms held under aeration. Specifically, it is the amount of BOD fed to the aerator (lbs/day) divided by the amount (lbs) of the Liquor Volatile Suspended Solids (MLVSS) mixture under aeration. Note: Some references use MLSS (Liquor Suspended Solids mixture) for eligibility, but MLVSS is considered more accurate for the size of microorganisms. Again, due to feasibility, COD is commonly used, as a substitute for BOD, because BOD takes five days for results.
Based on this control method, the amount of dissolved solids in the liquor mixture can be varied by removing the active sludge (WAS) or restoring the active sludge (RAS).
Plant type
There are various types of active sludge plants. These include:
Plant Package
There are different types of plant packages, often serving small communities or industrial plants that may use hybrid processing often involving the use of aerobic sludge to treat incoming waste. In such plants, the main stage of treatment completion can be eliminated. In this plant, biotic flocs are made which provide the required substrate. Plant packages are designed and manufactured by specialized engineering firms in dimensions that allow to transport them to work sites on public highways, usually wide and 12 times 12 feet high. The length varies with capacity with larger plants being made-cut and welded on site. Steel is preferred over synthetic materials (eg, plastics) for durability.
Plant packages are generally extended aeration variants, to promote 'fit & amp; forget 'the approach needed for small communities without dedicated operational staff. There are various standards to help their design.
To use less space, treat difficult waste, and intermittent flow, a number of designs from hybrid processing plants have been produced. Such plants often combine at least two stages of the three major stages of treatment into a single stage of composite. In the UK, where a large number of wastewater treatment plants serve small populations, plant packages are an alternative to building large structures for each stage of the process. In the US, packaged plants are typically used in rural areas, highway rests, and trailer parks.
Oxidation channel
In some areas, where more land is available, sewage is treated in a large round or oval trench with one or more horizontal aerators usually called brush aerators or discs that drive mixed drinks around the trenches and provide aeration. This is an oxidation trench, often referred to by trade names of manufacturers such as Pasveer, Orbal, or Carrousel. They have the advantage that they are relatively easy to maintain and are resistant to shock loads that often occur in smaller communities (ie at breakfast and at night).
Ditch oxidation installed generally as' fit & amp; forgot 'technology, with typical design parameters of hydraulic retention time of 24-48 hours, and mud life of 12 - 20 days. This is compared to nitrifying active sludge plants that have an 8 hour retention time, and a mud lifespan of 8-12 days.
Deep shaft/Vertical Treatment
Where the land is in a limited supply of waste water can be treated by injection of oxygen into a depressed mud flow injected into the base of the deep columnar tank buried in the soil. Such axis can reach up to 100 meters deep and filled with sewage. As oxygen upflow is forced into the solution by pressure at the base of the shaft breaks out as molecular oxygen which provides a very efficient source of oxygen for active sludge biota. Increased oxygen and reinjected sludge provide a physical mechanism for mixing waste and sludge. Mud and dirt mixture is poured on the surface and separated into supernatant and sludge components. The efficiency of inner shaft care can be high.
The surface aerators are generally quoted to have aeration efficiency of 0.5 to 1.5 kg O 2 /kWh, the aeration is spread as 1.5 - 2.5 kg O 2 /KWh. Deep Shaft claims 5 - 8Ã, kg O 2 /kWh.
However, construction costs are high. Deep Shaft has seen the biggest uptake in Japan, due to land issues. Deep Shaft was developed by ICI, as a spin-off of their Pruteen process. In the UK it is found in three locations: Tilbury, Anglian water, treating wastewater with high industry contribution; Southport, United Utilities, due to land space problems; and Billingham, ICI, once again treating industrial waste, and building (after Tilbury shafts) by ICI to help agents sell more.
DeepShaft is a licensed, licensed process. The license has changed several times and currently (2015) Noram Engineering sells it.
Water-treated containers
Most of the biological oxidation processes for industrial wastewater treatment have a similar use of oxygen (or air) and microbial action. The surface aeration container reaches 80 to 90% BOD removal with a retention time of 1 to 10 days. Basins can range from 1.5 to 5.0 meters and utilize a motor-driven aerator that floats on the surface of waste water.
In the aeration basin system, the aerator provides two functions: they transfer the air into the basin required by biological oxidation reactions, and they provide the necessary mixing to disperse the air and to contact the reactants (ie oxygen, waste water and microbes). Typically, a floating surface aerator is rated to provide an air equivalent of 1.8 to 2.7 kg O 2 /kWh. However, they do not provide the best mixing normally achieved in active sludge systems and therefore aeration basins do not reach the same level of performance as active sludge units.
The biological oxidation process is sensitive to temperature and, between 0 Â ° C and 40 Â ° C, the rate of biological reactions increases with temperature. Most surface aeration vessels operate between 4 Ã, Â ° C and 32 Ã, Â ° C.
Sequencing batch reactors (SBRs) treat waste water in batches in the same vessel. This means that the bioreactor and the final clarifier are not separated in space but in the order of the time. The installation consists of at least two tanks which are identically identical to the common inlet, which can be switched between the two. While one tank in the other settle/decant mode is aerating and charging.
src: i.ytimg.com
Aeration method
Spreading aeration
Liquid waste flows into the inner tank with a diffuser system aeration system attached to the floor. It's like the scattered airstone used in tropical fish tanks but on a much larger scale. The air is pumped through blocks and the curtain of bubbles forms the oxygenate of liquor and also provides the necessary mixing action. If the limited capacity or waste is very strong or difficult to maintain, oxygen can be used instead of air. Normally, air is generated by some type of blower or compressor.
Aerator surface (cone)
Vertically mounted tubes up to 1 meter in diameter extend from just above the base of the concrete tank to just below the surface of the liquid waste. A typical shaft may be 10 meters. At the end of the surface, the tube is formed into a cone with helical blades attached to the inner surface. When the tube is turned, the vane spits liquid up and out of the cone which draws the new waste liquid from the bottom of the tank. In many works, each cone is located in a separate cell that can be isolated from the remaining cells if necessary for maintenance. Some works may have two cones to the cell and some large works may have 4 cones per cell.
Pure oxygen aeration
A pure activated oxygen sludge aeration system is a tank-covered reactor tank with a surface type aerator impeller mounted in the tank at the surface interface of the oxygen carbon liquid. The amount of oxygen entrainment, or DO (Dissolved Oxygen), can be controlled by adjustable adjustment rate control, and oxygen-controlled oxygen gas vent valve gas. Oxygen is generated on the site by air cryogenic distillation, swing pressure adsorption, or other methods. This system is used where waste water treatment plants are at the high and high waste throughput required because high energy costs are involved in oxygen purification.
src: www.aireo2.com
Recent developments
A new development of the activated sludge process is the Nereda process that produces a precipitated granular deposit very well (the mud volume index decreases from 200-300 to 40 mL/g). A new process reactor system was created to take advantage of this fast settling sludge and integrated into the aeration tank rather than having a separate unit outside. About 30 Nereda wastewater treatment plants around the world operate, under construction or under design, with sizes varying from 5,000 to 858,000 equivalent people.
src: i.ytimg.com
History
The active sludge process was discovered in 1913 in England by two engineers, Edward Ardern and W.T. Lockett, who conducted the research for the Department of River Corporation at Davyhulme Sewage Works. This development leads to one of the most significant improvements in public health and the environment during this century.
In 1912, Dr. Gilbert Fowler, a scientist at the University of Manchester, observed experiments conducted at Lawrence Experiment Station in Massachusetts that involved aerated waste in algae-covered bottles. Fowler's engineering colleagues, Ardern and Lockett, experimented on treating waste in a draw-and-fill reactor, which resulted in highly treatable waste. They aerated the waste water continuously for about a month and were able to achieve complete nitrification of the sample material. Believing that the mud has been activated (in the same way as activated carbon), the process is named active sludge . It soon became apparent that what really happened was a means of centralizing biological organisms, separating fluid retention time (ideally, low, for concise treatment systems) from solids retention time (ideally, high enough, for low waste in BOD 5 and ammonia.)
The results were published in a seminal paper in 1914, and the first full-scale sustainable flow system was installed in Worcester two years later. In the aftermath of the First World War new treatment methods spread rapidly, especially to the United States, Denmark, Germany and Canada. In the late 1930s, active sludge treatment became a well-known biological wastewater treatment process in countries where sewer systems and general sewage treatment plants.
src: c8.alamy.com
See also
- Active sludge model
- Aeration lagoon
- aerobic granulation
- Aerobic granular reactor
- Aerobic treatment system
- Industrial wastewater treatment
- List of wastewater treatment technologies
- Membrane bioreactor
- Play biological contactors
- Sludge bulking
src: www.ultrawaves.de
References
src: i.ytimg.com
External links
- Aerated, Partial Mix Lagoons (Factsheet Wastewater Technology by the U.S. Environmental Protection Agency)
- Aerated Lagoon Technology (Linvil G. Rich, Professor Emeritus, Department of Engineering and Environmental Science, Clemson University)
Source of the article : Wikipedia
0 Comments