Most use surface aeration. The operation is mainly to control the amount of activated sludge and oxygen supply. The concentration of activated sludge referred to as mixed liquid suspended solids in the aeration tank can be adjusted, that is, the amount and load rate of activated sludge can be adjusted. During operation, attention should be paid to adjusting according to specific conditions.
Activated sludge sewage treatment plant is prone to sludge swelling, that is, the sludge has a very high moisture content and is not easy to settle.
This will cause the sludge to flow out of the sedimentation tank with water and damage the water quality. At the same time, the loss of sludge will reduce the sludge in the aeration tank, and the entire process will gradually fail.
When the sludge is found to have a tendency to swell, the cause should be analyzed immediately and measures taken. In the biological treatment of wastewater, microorganisms are suspended in water. The suspended microbial community is named for its mud-flower state flocculation. Generally refers to the aerobic activated sludge process. When activated sludge comes into contact with wastewater in the basic process, it not only absorbs some pollutants as nutrients, but also absorbs and traps other pollutants such as colored substances and suspended solidswhich has a good treatment effect.
The basic mechanism is manifested in the biological treatment of water. The basic flow of the activated sludge process Figure 1 is as follows. The characteristics of activated water not only meet the basic requirements of national drinking water hygiene standards, but also have some special functions that are beneficial to human health.
According to different processing technologies and additional functions, the products currently on the market include mineralized water, magnetized water, electrolytic ion water, natural backwater and so on.
The wastewater in the aeration tank is fully mixed and contacted with the accumulated activated sludge, and the pollutants are transferred to the sludge. The microorganisms use the pollutants as nutrients and obtain oxygen from the water for growth and reproduction biomass. Some metabolites Such as carbon dioxide and ammonia are present in water to enter.
Then, the mixed liquid flows through the sedimentation tank, the mud and water are separated, the effluent is treated, the sludge flows back to the inlet of the aeration tank, and the process is repeated to enter. Organic matter that cannot be metabolized by microorganisms is more or less left in the water and cannot be removed. Due to lack of contact or time, some metabolizable soluble substances will also be left, and incomplete separation of mud and water will also reduce the quality of the effluent.
In order to reduce the load of the aeration tank, a primary clarifier is set up before the aeration tank, and the latter is usually called a secondary clarifier. The main factors affecting the working efficiency treatment efficiency and economic benefits of activated sludge process are the choice of treatment method and the design and operation of aeration tank and sedimentation tank.
Methods In addition to the ordinary activated sludge method, there are a multi-point water inlet method, an adsorption regeneration method, an extended aeration method, and a high-load activated sludge method. The first two methods are different from the basic process, and the amount and location of sewage entering the aeration tank are also different.
In the multi-point inflow activated sludge method, only a part of the wastewater and the returned sludge enter the pond together at the head end. The rest of the wastewater is divided into times at a distance of inlets the inlet spacing is generally equal from the head end into the aeration tank. From the point of view of the process, it can be said that the adsorption and regeneration of activated sludge method Figure 2 is only a deformation of the multi-point water intake process Figure 3.
Only the last of several wastewater inlets was used, the latter becoming the former. The development of method types is based on a process mechanism.
The main substances involved in this process are: organic matter, microorganisms and dissolved oxygen air. The first two are the main ones.The activated sludge AS process is a type of suspended growth biological wastewater treatment that is used for treating both municipal sewage and a variety of industrial wastewaters.
Economical modeling and cost estimation of activated sludge processes are crucial for designing, construction, and forecasting future economical requirements of wastewater treatment plants WWTPs. In this study, three configurations containing conventional activated sludge CASextended aeration activated sludge EAASand sequencing batch reactor SBR processes for a wastewater treatment plant in Tehran city were proposed and the total project construction, operation labor, maintenance, material, chemical, energy and amortization costs of these WWTPs were calculated and compared.
Wastewater treatment plants WWTPs are complex systems which include a large number of biological, physicochemical, and biochemical processes Sotomayor et al. Actually, activated sludge systems are a type of suspended growth biological wastewater treatment in which the degradation and removal of contaminants within the wastewater is performed by microorganisms [bacterial biomass suspension the activated sludge ] Evans Many researchers have modeled and simulated the activated sludge process Evans ; Jeppsson ; Chachuat et al.
A review on the historical evolution of the activated sludge process can be found in the work of Jeppsson A number of modifications to the design and operational conditions of the conventional activated sludge process have been developed for the specific purposes of domestic and industrial wastewater treatment.
The conventional activated sludge CAS process is designed with a plug flow reactor and continuous influent wastewater. A large number of variations of the conventional activated sludge process have been designed to improve system performance by modifying the reactor layout, aeration system, influent pattern, and operational conditions. Some of the more widely used modified activated sludge processes include completely mixed activated sludge, step-feed activated sludge, extended aeration activated sludge EAASsequencing batch reactor SBRoxidation ditch, membrane bioreactor MBR processes, etc.
Evans Sotomayor et al. Benedetti et al. It is, therefore, a flexible instrument to cope with the flexibility and complexity of integrated water management regulations. Lee et al. Dynamic optimization is a powerful tool for assisting engineers in determining optimal operations and designs for activated sludge processes.
Hreiz et al. Karpinska and Bridgeman reviewed computational fluid dynamics CFD -aided modeling of activated sludge systems in which the rationale behind the use of CFD to model aeration, facilitating enhancement of treatment efficiency and reduction of energy input were discussed. In the field of wastewater treatment, there is an increasing requirement to improve effluent quality for the benefit of receiving surface waters.Biological treatment process with high quality effluent, low maintenance, and low operations requirements.
Extended Aeration plants provide a low cost, odor and nuisance-free Sewage Treatment Plant that produces a high degree of treatment. Extended aeration treatment plants are used worldwide to provide simple and effective wastewater treatment. The Extended Aeration Process, a modification of the Activated Sludge Process, effectively treats the contaminants in wastewater.
The standard basis of design includes an aeration system, providing a hour detention time and a final settling tank, with an effective 4-hour detention time. Diffused air is introduced into the aeration tank, this provides the proper environment for the development of aerobic bacteria. These bacteria thrive on the materials contained in the wastewater.
The prolonged period of aeration, in addition, oxidizes a portion of the solids in the system. Oxygenation by diffused aeration provides operating flexibility and standby reserve to meet the demanding requirements of varied package plant applications.
Separation of the solids from the mixed liquor developed in the aeration tank takes place in the settling compartment. The clarified effluent is withdrawn for reuse or discharged into a receiving stream from the top of the settling tank.
The settled solids are rapidly pumped from the bottom of the settling tank back to the aeration system. Only minimal routine housekeeping and operational tasks are required of the plant operator. Extended Aeration Systems Biological treatment process with high quality effluent, low maintenance, and low operations requirements.Extended aeration is a method of sewage treatment using modified activated sludge procedures. It is preferred for relatively small waste loads, where lower operating efficiency is offset by mechanical simplicity.
Mechanized sewage treatment typically includes settling in a primary clarifierfollowed by biological treatment and a secondary clarifier. Both clarifiers produce waste sludge requiring sewage sludge treatment and disposal. Activated sludge agitates a portion of the secondary clarifier sludge in the primary clarifier effluent.
Remaining secondary sludge and all primary sludge typically require digestion prior to disposal. Extended aeration agitates all incoming waste in the sludge from a single clarifier.
The combined sludge starts with a higher concentration of inert solids than typical secondary sludge and the longer mixing time required for digestion of primary solids in addition to dissolved organics produces aged sludge requiring greater mixing energy input per unit of waste oxidized.
Extended aeration is typically used in prefabricated "package plants" intended to minimize design costs for waste disposal from small communities, tourist facilities, or schools.
In comparison to traditional activated sludge, longer mixing time with aged sludge offers a stable biological ecosystem better adapted for effectively treating waste load fluctuations from variable occupancy situations. Supplemental feeding with something like sugar is sometimes used to sustain sludge microbial populations during periods of low occupancy; but population response to variable food characteristics is unpredictable, and supplemental feeding increases waste sludge volumes.
Sludge may be periodically removed by septic tank pumping trucks as sludge volume approaches storage capacity. From Wikipedia, the free encyclopedia. Hammer, Mark J. Water and Waste-Water Technology. ISBN Wastewater Engineering. McGraw-Hill Book Company. Steel, E. Water Supply and Sewerage, 5th Edition.The extended aeration process is one of the modifications of the ASP. It is a complete mix system and provides biological treatment for the removal of biodegradable organic wastes under aerobic conditions.
Air may be supplied by mechanical or diffused aeration to provide the oxygen required to sustain the aerobic biological process.
Mixing must be provided by aeration to maintain the microbial organisms in contact with the dissolved organics. Since there is complete stabilization is occurred in the aeration tank, there is no need for separate sludge digester.
Further primary settling tank is also omitted and settleble organic solids are also allowed to settle in the aeration tank due to long detention time in the aeration tank. Process flow diagram of extended aeration system is furnished below.
Disadvantages of extended aeration system:. Related Topics: Advantages and disadvantage of aeration system Advantages of extended Aeration System: Plants are easy to operate, Cage Rotor Cage Rotor One or more mechanical surface aerators with horizontal We are the contracting co.
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June 3, at pm. March 30, at am. March 1, at pm. Leave a Reply Click here to cancel reply. Water Treatment Search. Water Treatment Related.Notice : This chapter includes some pics related to explanatory tables in accordance with the subject For a faster connecting, in the other words, for your convenience, tables were marked by the icon :instead of themselves You will find the content of the table just after this icon To access the table you want, just click on the explanatory item coloured in red In addition, all the other pics have thumbnails Just click on them for larger size A prefabricated package plant is to be used to treat the wastewater from a resort area consisting of individual family residences.
The average occupancy has been estimated to be 2. Use an hourly peaking factor of 4 for sizing the sedimentation facilities. Select the type of package plant and size the principal components of the plant. The total number of person : home 2. Design Example of SBR A sequencing batch reactor activated - sludge process is to be used to treat wastewater with the characteristics given below.
Determine the mass of suspended solids in the reactor over a 7 - day operating period. Determine also the depth of clear liquid measured from the top of the settled sludge to the lowest liquid level reached during the decant cycle.
Use the following design criteria and constraints. Calculation of Oxygen Requirement Calculate oxygen requirement of a complete - mix activated sludge process treating domestic wastewater having flowrate of 0.
The effluent soluble BOD 5 is 6. Design Example of Final Settling Tank A column analysis was run to determine the settling characteristics of an activated sludge suspension. The results of the analysis are shown below. Plot solids flux vs. MLSS concentration as shown below. The value of G at the intersection, 2. Determine total solids loading to the clarifier.
Introduction to Activated Sludge Process–Sewage Treatment
Determine the surface area of the clarifier. Calculate the diameter of the clarifier. Check clarification function. Because m 2 2the thickening function governs the design. Influent parameters.
Approximate tank size. Secondary clarifier. Sludge handling. Days storage in aeration tank.In IDEA process a period of aeration, sedimentation and a period of discharge occur repeatedly in a reactor and the inlet flow enters the bottom of the reactor, where it is slowly dispersed.
The treated wastewater is then discharged intermittently during the discharge period. The first phase: aeration, involves rapid surface mixing to mix the influent with the activated sludge. The mixing action aids in dissolving oxygen into the water whilst forcing the sludge into suspension from its settled state. Alum is added to bind the phosphorous present in the sewage, allowing it to settle out. Nitrification also occurs at this stage to convert ammonia to nitrite. The second phase: Settling occurs when the surface aerators are stopped, which allows solids to migrate to the bottom of the tank.
At this stage, anoxic conditions predominate in the sludge due to the lack of molecular oxygen, which cause the bacteria in the sludge to use oxygen the bound in nitrates NO3— for metabolism.
This results in the effusion of nitrogen as a gas. The third phase: During decanting, a trough is skimmed across the top layer of the tank, collecting the water to be sent off for further processing in downstream processes. Also, phosphorus removal is one of the benefits of this process. The biological reactors, i. Due to the above reasons, huge amount of inventory cost can also be saved. As such, the sludge generated is well stabilized and does not require further digestion in a sludge digester.
Save my name, email, and website in this browser for the next time I comment. Intermittently Decanted Extended Aeration IDEA In IDEA process a period of aeration, sedimentation and a period of discharge occur repeatedly in a reactor and the inlet flow enters the bottom of the reactor, where it is slowly dispersed. About the Author: aslani. Related Posts. March 27th, 0 Comments. Leave A Comment Cancel reply Comment. Go to Top.