What is the purpose of activated sludge in sewage treatment?
Civil Engineering. Civil Engineering questions and answers. 4. A conventional activated sludge process is used in the secondary treatment step of a municipal wastewater treatment plant treating a flow rate (Q) of 2,000 m3/d with an influent BOD concentration (S.) of 400 mg/L. a) The aeration tank is operated at an MLSS concentration of 3,500 mg TSS/L and a hydraulic …
What is the general arrangement of an activated sludge process?
The activated sludge process is a type of wastewater treatment process for treating sewage of industrial wastewaters using aeration and a biological floc composed of bacteria and protozoa. An activated sludge tank with dimensions of 30 m*30 m*200m (W x H x L), is designed as a plug-flow reactor and it receives an influent BOD of 200 mg/L with a ...
How is activated sludge used in biogas production?
Activated sludge is a biological process that utilizes microorganisms to convert organic and certain inorganic matter from wastewater into cell mass. The activated sludge is then separated from the liquid by clarification. The settled sludge is either returned (RAS) or wasted (WAS). Activated sludge is commonly used as a wastewater treatment process
Why are there bubbles in my activated sludge tank?
The activated sludge process is one of the most commonly used for secondary wastewater treatment. As a suspended-growth biological treatment process, activated sludge utilizes a dense microbial culture in suspension to biodegrade organic material under aerobic conditions and form a biological floc for solid separation in the settling units.
What stage is activated sludge used?
In a sewage (or industrial wastewater) treatment plant, the activated sludge process is a biological process that can be used for one or several of the following purposes: oxidizing carbonaceous biological matter, oxidizing nitrogenous matter: mainly ammonium and nitrogen in biological matter, removing nutrients ( ...
What is activated sludge in sewage treatment?
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 steps of activated sludge process?
Treatment StepsStep 1: Screening and Pumping. ... Step 2: Grit Removal. ... Step 3: Primary Settling. ... Step 4: Aeration / Activated Sludge. ... Step 5: Secondary Settling. ... Step 8: Oxygen Uptake. ... Sludge Treatment.
Where is activated sludge used?
In a sewage (or industrial wastewater) treatment plant, the activated sludge process can be used for one or several of the following purposes: oxidizing carbonaceous matter: biological matter. oxidizing nitrogeneous matter: mainly ammonium and nitrogen in biological materials. removing phosphate.
Why activated sludge process is used?
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. The goal is to maintain aerobic conditions and to keep the activated sludge suspended.Feb 10, 2021
What is sewage treatment?
Sewage Treatment refers to the process of removing contaminants, micro-organisms and other types of pollutants from wastewater. Wastewater, or raw sewage, is water that drains from toilets, sinks, showers, baths, dishwashers, washing machines and liquid industrial waste.
What are the 3 stages of sewage treatment?
There are three main stages of the wastewater treatment process, aptly known as primary, secondary and tertiary water treatment.Dec 6, 2018
Which step gives most of the sludge?
Answer: Secondary treatment stage of polluted water in sewage treatment plant gives most of the sludge.Feb 17, 2021
What are the 7 steps in wastewater treatment?
The Wastewater Treatment ProcessStage One — Bar Screening. ... Stage Two — Screening. ... Stage Three — Primary Clarifier. ... Stage Four — Aeration. ... Stage Five — Secondary Clarifier. ... Stage Six — Chlorination (Disinfection) ... Stage Seven — Water Analysis & Testing. ... Stage Eight — Effluent Disposal.Mar 5, 2021
How does activated sludge treatment help in secondary treatment?
Activated sludge is a common suspended-growth method of secondary treatment. Activated sludge plants encompass a variety of mechanisms and processes using dissolved oxygen to promote growth of biological floc that substantially removes organic material.
What are the different ways of treatment of sludge?
The most common treatment options include anaerobic digestion, aerobic digestion, and composting. Sludge digestion offers significant cost advantages by reducing sludge quantity by nearly 50% and providing biogas as a valuable energy source.
What is 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. From: Resource-Efficient Technologies, 2016.
How does activated sludge work?
The activated sludge process (Fig 12.4) uses microorganisms to feed organic contaminants that are in wastewater to produce a high-quality effluent. The basic principle behind all activated sludge processes is that as microorganisms grow, they form particles that clump together. These particles, which are referred to as floc, are allowed to settle to the bottom of the tank, which results in a relatively clear liquid free organic material and suspended solids. The screened wastewater is mixed with varying amounts of recycled liquid that contains a high proportion of organisms that are taken from a secondary tank, and it becomes a product that is called mixed liquor. The next step for the mixture is to stir and inject it with large quantities of air to provide oxygen and keep the solids in suspension. After a period of time, the mixed liquor flows to a clarifier where it is allowed to settle. During this settling a portion of the bacteria is removed and the partially cleaned water flows on for additional treatment. The settled solids that resulted, the activated sludge, are then returned to the first tank to begin the process again. The basic activated sludge process consists of several interrelated components:
What is the major phenomenon responsible for PPCPs elimination in activated sludge process?
Biodegradation is suggested as the major phenomenon responsible for PPCPs elimination in activated sludge process. Therefore, to improve the degradation of PPCPs, an effective strategy must be adapted to increase the decomposition.
Why do activated sludge plants foam?
Foaming in activated sludge plants is caused by high SRTs, warm temperatures, low F:M ratios and high MLSS levels, as well as oil and grease and/or surfactants in the influent. Abundance of actinomycetes such as Nocardia or Microthrix are commonly related to foaming in activated sludge plants, and have been identified in a full-scale MBR plant subject to variable OLRs ( Smith, 2006 ). However, foam in MBR plants has been observed in the absence of actinomycetes. The degree of foaming is reported as being related to the protein EPS concentrations (Nakajima and Mishima, 2005). Foaming sludges also appear to yield lower membrane permeabilities ( Chang and Lee, 1998 ), attributed to the higher hydrophobicity of foaming activated sludge ( Section 2.3.6.4 ). Foaming thus provides an indication of sludge fouling propensity.
How many Ascaris eggs are in activated sludge?
The concentration of parasites in activated sludge treated effluents is usually low at less than 5 eggs/l, though higher numbers of around 60 Ascaris eggs/l have been reported ( Bhaskaran et al., 1956 ). Numbers of protozoan (oo)cysts in activated sludge effluents can be high despite relatively high removal rates.
What is activated sludge?
Activated sludge is a sludge particles reduced in wastewater by the growth of organisms in aeration tanks. The term ‘activated’ comes from the fact that the particles teem with bacteria, fungi, and protozoa and is different from primary sludge in the sense that the sludge particles contain many living organisms that can feed on the incoming wastewater. Described simply, screened wastewater is mixed with varying amounts of recycled liquid containing a high proportion of organisms taken from a secondary clarifying tank, and it becomes a product called mixed liquor. This mixture is stirred and injected with large quantities of air, to provide oxygen and keep solids in suspension. After a period of time, mixed liquor flows to a clarifier where it is allowed to settle. A portion of the bacteria is removed as it settles, and the partially cleaned water flows on for further treatment. The resulting settled solids, the activated sludge, are returned to the first tank to begin the process again. Today a number of variations of the basic process have been developed. This issue of Pipeline includes descriptions of three of the most common variations: Extended aeration, sequencing batch reactors, and oxidation ditches. The activated sludge plant is the most popular biological treatment process for larger installations. A glossary of terms that are used in activated sludge process is reflected as under: Aerobic – a condition where oxygen is present BOD – biological oxygen demand. Measure of oxygen organic material in the water requires.
What is activated sludge treatment?
Activated sludge treatment process is widely used in the treatment of municipal sewage and industrial waste waters due to the fact that it’s economically viable and reasonably safe to operate. Such a system can be used in large installations. However it’s very important to have compatible design parameters to be infused while designing Activated Treatment Plant. Moreover, air requirement, MLSS, MLVSS, etc. are very important parameters to be maintained in the system. The present paper deals with these aspects to impart an over view of the conceptualization along with system design.
What is the oxygen requirement for activated sludge?
The total oxygen requirement of the process may be formulated as follows: O2 required (g/d) = Q(SO - S) - 1.42 QwXr
What are the considerations for design of activated sludge plant?
The items for consideration in the design of activated sludge plant are aeration tank capacity and dimensions, aeration facilities, secondary sludge settling and recycle and excess sludge wasting
How does a secondary settling tank work?
Secondary settling tanks, which receive the biologically treated flow undergo zone or compression settling. Zone settling occurs beyond a certain concentration when the particles are close enough together that interparticulate forces may hold the particles fixed relative to one another so that the whole mass tends to settle as a single layer or "blanket" of sludge. The rate at which a sludge blanket settles can be determined by timing its position in a settling column test whose results can be plotted as shown in figure. Compression settling may occur at the bottom of a tank if particles are in such a concentration as to be in physical contact with one another. The weight of particles is partly supported by the lower layers of particles, leading to progressively greater compression with depth and thickening of sludge. From the settling column test, the limiting solids flux required to reach any desired underflow concentration can be estimated, from which the required tank area can be computed.
How much oxygen can an aerator give?
Assume oxygenation capacity of aerators at field conditions is only 70% of the capacity at standard conditions and mechanical aerators are capable of giving 2 kg oxygen per kWh at standard conditions .
What is activated sludge treatment?
This process utilizes a multi-chamber reactor unit that uses microorganisms as a method to remove nutrients from the water. Oxygen is used to establish and regulate aerobic conditions and to suspend the sludge.
What is required to design and construct an activated sludge system?
Experts are required to design and construct the activated sludge system. Skilled personnel must operate and maintain the treatment of activated sludge. Electricity must be continuously used, increasing wastewater treatment energy consumption. Parts and materials may not be available on a local level.
How is wastewater mixed?
Wastewater is mixed and aerated in a special tank. This step in the process occurs by pumping air or oxygen into the activated sludge tank or using surface aerators. The process oxidizes organic matters in the wastewater, producing new cells, carbon dioxide, and water.
Why is oxygen used in wastewater treatment?
Oxygen is used to establish and regulate aerobic conditions and to suspend the sludge. The activated sludge wastewater treatment provides many advantages, but it may not be appropriate in all situations.
Where do bacteria settle in activated sludge?
Live bacteria settle to the bottom of the tank and dead bacteria float to the top. Clean water is discharged into a soakaway or watercourse while the live bacteria return to the digestion chamber. It is important to understand what activated sludge is to comprehend how the complete activated sludge system works.
Is activated sludge treatment good for all applications?
The activated sludge treatment process does have some drawbacks and may not be appropriate for all applications. Some disadvantages associated with activated sludge include: There are initial high capital and operating costs that may deter some facilities from utilizing this method.
Is activated sludge sewage treatment centralized?
Activated sludge sewage treatment is ideally completed in a centralized treatment facility. The treatment of activated sludge can occur in most climates. However, colder environments reduce the treatment capacity.
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.
When was activated sludge discovered?
The activated sludge process was discovered in 1913 in the United Kingdom by two engineers, Edward Ardern and W.T. Lockett, who were conducting research for the Manchester Corporation Rivers Department at Davyhulme Sewage Works. This development led to arguably the single most significant improvement in public health and the environment during ...
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.
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.
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 is complete mix activated sludge achieved?
In a rectangular tank, complete mixing is achieved by distributing the sewage and the return sludge uniformly along one side of the tank and withdrawing the aerated sewage, uniformly along the opposite side. In case of circular or square tank, complete mixing is achieved by mechanical aerator with adequate mixing capacity installed at the centre of the tank.
What is secondary sludge?
Secondary sludge is either returned and wasted within each stage, or sometimes the excess sludge from the second stage is recycled to the first stage and from there, both the sludge are disposed off. This process is most suited for treating the strong industrial sewage which has high value of B.O.D. Type # 5.
What is activated aeration?
Activated Aeration: It is a combination of two tapered activated sludge plants in parallel using the same settled sewage as influent. The excessive activated sludge of one plant is used as seeding for another plant, which is called activated aeration.
What happens when sewage is added to the returned sludge?
If the sewage is added to the returned sludge at more than two points along the aeration channel, the load coming on the returned sludge is changing. In the previous article, it has been stated that the B.O.D. of the mixed liquor is different at different points.
How long does it take for sewage to be aerated?
The sewage is aerated along with return sludge for a comparatively short period of 0.5 to 1.5 hrs, when the sludge absorbs the organic matter in the sewage.
What is the disadvantage of a two stage aeration system?
The main disadvantage is that the sludge becomes septic soon and requires early removal and disposal from the settling tanks. Type # 4. Two-Stage Aeration: In two-stage aeration the sewage is allowed to flow in a pair of aeration and sedimentation units.