To reiterate, RAS is needed to progress with the aeration digestion process. WAS is the excess micro organisms (more than that is needed) This matter is removed and may be gainfully used in another process viz.composting cured of bio-mass, Etc. A balance is maintained in all the anaerobic and aerobic processes of a treatment system.
What is the purpose of Ras in wastewater treatment system?
A balance is maintained in all the anaerobic and aerobic processes of a treatment system . Well wishes for nature's process. I agree Mohamed Hasnain Isa " The purpose of Return Activated Sludge (RAS) is to prevent loss of microorganisms from the aeration tank and maintain an adequate population for treatment of the wastewater.
What is Return Activated Sludge (RAS)?
The purpose of Return Activated Sludge (RAS) is to prevent loss of microorganisms from the aeration tank and maintain an adequate population for treatment of the wastewater. As microbes metabolize their substrate, they grow and multiply in number.
What is the difference between Ras and was?
This returned material is the return activated sludge (RAS). The material that is not returned, the waste activated sludge (WAS), is removed for treatment and disposal. The clarified wastewater then flows over a weir and into a collection channel before being diverted to the disinfection system.
What happens to wastewater in a treatment plant?
Most homes and businesses send their wastewater to a treatment plant where many pollutants are removed from the water. Wastewater treatment facilities in the United States process approximately 34 billion gallons of wastewater every day. Wastewater contains nitrogen and phosphorus from human waste, food and certain soaps and detergents.
Was and RAS in wastewater treatment?
Waste Activated Sludge (WAS) – The activated sludge (excess biomass or cell mass) removed from the secondary treatment process. For most treatment plants, this will be a portion of the Return Activated Sludge (RAS) flow stream.
What does RAS stand for in wastewater?
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 SAS and Ras?
The settled biomass, called Return Activated Sludge (RAS), is then returned to the beginning of the aeration process where it will absorb fresh sewage to start the process again. This enables the process to operate as a continuous cycle. Surplus Activated Sludge (SAS)
Was and Ras pumps?
It includes return activated sludge (RAS), which is continuously pumped back into the secondary biological treatment tank as part of the treatment process, and waste activated sludge (WAS), which is excess from settled sludge that is pumped to the sludge handling process.
What is the important of return activated sludge Ras in the treatment process?
The purpose of Return Activated Sludge (RAS) is to prevent loss of microorganisms from the aeration tank and maintain an adequate population for treatment of the wastewater. As microbes metabolize their substrate, they grow and multiply in number.
What is Ras flow?
(RAS) rate. Influent flow distribution/ splitting SLR is defined as the quantity of solids applied per unit of surface area of the secondary clarifiers in service.
Why is activated sludge called activated?
They aerated the waste-water continuously for about a month and were able to achieve a complete nitrification of the sample material. Believing that the sludge had been activated (in a similar manner to activated carbon) the process was named activated sludge.
What is the use of activated sludge?
The activated sludge system (aeration and sedimentation tanks) is the main representative of the suspended-growth aerobic system. The activated sludge is the most widely used method to bring about stabilization in wastewater having organic matter constituents.
What is the purpose of the secondary settling tank in an activated sludge plant?
These settling tanks are often termed clarifiers and are used in activated sludge systems for separating treated water from biomass, settling sludge and sufficiently thickening it so that when the sludge is returned to the tank inlet, it can maintain the biomass concentration levels required.
What causes sludge bulking?
Abstract. Sludge bulking is the most common solids settling problem in wastewater treatment plants, which is caused by the excessive growth of filamentous bacteria extending outside the flocs, resulting in decreasing the wastewater treatment efficiency and deteriorating the water quality in the effluent.
Why is the sludge aerated?
Why is the sludge aerated? Explanation: An activated-sludge reactor is a system in which pre-treated sewage (i.e. having passed through primary treatment) is aerated to promote the growth of bacteria (cells) that gradually consume the organics in the sewage.
What is SAS in wastewater treatment?
Excess or Surplus Activated Sludge (SAS) has to be regularly removed from the process to maintain the correct balance between the biomass and the wastewater entering the process.
Why Treat Wastewater?
It's a matter of caring for our environment and for our own health. There are a lot of good reasons why keeping our water clean is an important priority:
Wastewater treatment
The major aim of wastewater treatment is to remove as much of the suspended solids as possible before the remaining water, called effluent, is discharged back to the environment. As solid material decays, it uses up oxygen, which is needed by the plants and animals living in the water.
Where is the Aldie Wastewater Treatment Plant located?
The Aldie Wastewater Treatment Plant, located inAldie , Virginia, is an extended aeration facilitywhich treats an average of 0.0031 MGD with adesign flow of 0.015 MGD. This technology waschosen because it would allow the area to meetpermit requirements while minimizing land use.The plant consists of an influent chamber whichdirects the flow to two parallel aeration basins,parallel clarifiers, and a UV disinfection system.
What is extended aeration?
The extended aeration process is one modificationof the activated sludge process which providesbiological treatment for the removal ofbiodegradable organic wastes under aerobicconditions. Air may be supplied by mechanical ordiffused aeration to provide the oxygen required tosustain the aerobic biological process. Mixing mustbe provided by aeration or mechanical means tomaintain the microbial organisms in contact withthe dissolved organics. In addition, the pH must becontrolled to optimize the biological process andessential nutrients must be present to facilitatebiological growth and the continuation of biologicaldegradation.
What is sequencing batch reactor?
sequencing batch reactor (SBR) is a variation ofthe activated sludge process. As a fill and draw orbatch process, all biological treatment phases occurin a single tank. This differs from the conventionalflow through activated sludge process in that SBRsdo not require separate tanks for aeration andsedimentation (Kappe, 1999). SBR systems containeither two or more reactor tanks that are operated inparallel, or one equalization tank and one reactortank. The type of tank used depends on thewastewater flow characteristics (e.g. high or lowvolume). While this setup allows the system toaccommodate continuous influent flow, it does notprovide for disinfection or holding for aeratedsludge.
Where are package treatment plants used?
They are most often used inremote locations such as trailer parks, highway restareas, and rural areas.
What is an oxidation ditch?
Oxidation ditches are suitable for facilities thatrequire nutrient removal, have limitations due to thenature of the site, or want a biological system thatsaves energy with limited use of chemicals unlessrequired for further treatment. Oxidation ditchtechnology can be used to treat any type ofwastewater that is responsive to aerobicdegradation. In addition, systems can be designedfor denitrification and phosphorous removal.
What is tertiary wastewater treatment?
Tertiary (or advanced) treatment removes dissolved substances, such as colour, metals, organic chemicals and nutrients like phosphorus and nitrogen.
What are the different levels of wastewater treatment?
There are several levels of wastewater treatment; these are primary, secondary and tertiary levels of treatment. Most municipal wastewater treatment facilities use primary and secondary levels of treatment, and some also use tertiary treatments.
How to reduce pressure on septic system?
Following some water conservation practices can greatly reduce pressure on your septic system. For more information about conserving water, see the fact sheet about Water Consumption. Here are a few things that you can do to care for your septic system: 1 Do not use your drain or toilet as a garbage disposal; avoid putting dental floss, diapers, coffee grounds and paper towel down the drain, as they can clog up your septic system. 2 Spread your loads of laundry out over the week. When too much water is added to the septic tank, it does not have time to treat wastes, and you could be flooding your drainfield with wastewater. 3 Plant grass on your drainfield, but keep trees and shrubs away from it, because roots can clog the system and cause damage. 4 Do not drive on your drainfield, because this can compact the soil and damage the septic system components.
Why is oxygen important in wastewater treatment?
The oxygen helps the bacteria to digest the pollutants faster. The water is then taken to settling tanks where the sludge again settles, leaving the water 90 to 95 percent free of pollutants. The picture below shows the settling tanks in the Winnipeg Wastewater Treatment Plant.
What is the process of removing pollutants from water?
Another natural method is called rapid infiltration, which is a process where a basin is filled with wastewater, which has already gone through a pre-treatment. The ground acts as a filter and removes the pollutants from the water. This method is similar to what happens in a septic system.
What is the process of tertiary treatment?
One of the biological treatment processes is called Biological Nutrient Removal (BNR). This diagram shows the treatment steps that Saskatoon wastewater goes through. Biological Nutrient Removal Process.
What is the Canadian Environmental Protection Act?
The Canadian Environmental Protection Act governs the release of toxic substances into the environment and allows the federal government to develop regulations for the use of toxic substances. Most provincial and territorial governments have legislation regarding wastewater treatment standards and requirements.
Why upgrade wastewater treatment system?
Enhanced treatment systems enable some wastewater plants to produce discharges that contain less nitrogen than plants using conventional treatment methods . Upgrading wastewater treatment systems is often expensive for municipalities and rate payers, but upgrades can pay for themselves or end up saving a plant money.
How does a septic system contribute to nutrient pollution?
Septic systems can easily become a source of nutrient pollution if not properly maintained. Most homes and businesses send their wastewater to a treatment plant where many pollutants are removed from the water. Wastewater treatment facilities in the United States process approximately 34 billion gallons of wastewater every day.
What is the source of nitrogen and phosphorus in wastewater?
Wastewater contains nitrogen and phosphorus from human waste, food and certain soaps and detergents. Once the water is cleaned to standards set and monitored by state and federal officials, it is typically released into a local water body, where it can become a source of nitrogen and phosphorus pollution. Some wastewater treatment plants are able ...
How to maintain a septic system?
Homeowners are responsible for maintaining their septic systems in most cases. To protect and maintain their system, homeowners should: 1 Have their system inspected regularly and pump their tank as necessary 2 Use water efficiently 3 Not dispose of household hazardous waste in sinks or toilets 4 Avoid driving vehicles or placing heavy objects on their drainfield 5 Visit EPA's decentralized wastewater (septic) systems webpage to learn more about septic systems and EPA's SepticSmart Week Program 6 Consult EPA's guide on maintaining septic systems for more information: Homeowner's Guide to Septic Systems (PDF) (9 pp, 3 MB, About PDF)
What causes a septic system to fail?
Common causes of septic system failure include aging infrastructure, inappropriate design, overloading with too much wastewater in too short a period of time and poor maintenance.
Who is responsible for septic system maintenance?
Homeowners are responsible for maintaining their septic systems in most cases. To protect and maintain their system, homeowners should: Have their system inspected regularly and pump their tank as necessary. Use water efficiently. Not dispose of household hazardous waste in sinks or toilets.
What percentage of homes in the US have septic systems?
Septic Systems. Approximately 20 percent of homes in the United States use septic systems that locally treat their wastewater. When a septic system is improperly managed, elevated nitrogen and phosphorus levels can be released into local water bodies or ground water.
What causes cloudy effluent?
For any conventional activated-sludge process , the probable causes of cloudy effluent include that mixed-liquor suspended solid ...
How to solve a problem using guidelines and procedures?
To solve a problem using guidelines and procedures: 1) identify the problem, 2) determine the most likely cause and 3) consider suggested remedies or corrective measures. In identifying a problem, visual observation of the treatment process is essential and settle-ability tests are vital. Settling-test observations lead to appropriate remedies ...
Introduction
In this post I'm going to discuss how you can estimate the solids concentration in the return activated sludge (RAS) using the treatment plant influent flow rate, the RAS flow rate, and the mixed liquor suspended solids (MLSS) concentration. This approach is new for me, having read about it in a great, new textbook from Eric J.
Favorite Textbook
My new favorite wastewater textbook is “Activated Sludge Wastewater Treatment” (Process Control & Optimization for the Operations Professional) by Eric J. Wahlberg. The book is published by DEStech Publications, Inc. ( www.destechpub.com ), ISBN No. 978-1-60595-333-5.
Putting Equation 1 To The Test!
Let's use the aforementioned data set I have to test how well Equation 1 from above, as taken from Dr. Wahlberg's book (Equation 6.6 in the textbook), holds up. I stated I had a "good" data set, not an "excellent" data set. From one year of data I had to do some data cleaning, deleting duplicate values, obvious data entry errors, etc.
Hypothesis Testing
From Table 1 it is easy to see that the mean actual RAS TSS values vs the mean Wahlberg-Predicted RAS TSS values are similar.
The Careful Observer
The careful observer will note what seems to be very high TSS concentrations for the return activated sludge from the two clarifiers. Recall from Table 1 that the RAS from Clarifier A had a mean TSS concentration of 28,549 mg/L and Clarifier B had a mean TSS concentration of 22,433 mg/L.
MLSS Data
In Figure 8 you can see the concentration of MLSS for both aeration tanks. Not only are the concentrations on the high side, but you can also see how difficult it is to balance the MLSS concentrations between the two tanks without flow measurement available on the influent to each aeration tank.
Final Observations
The high total suspended solids concentration in the return activated sludge from both clarifiers can partially be explained by the presence of excessive inert material in both MLSS streams flowing to the clarifiers. In Figure 15 you can see that the mean MLVSS/MLSS ratio is 59% for both tanks. This is low.
What is activated sludge?
The activated sludge process is a biological process ( Read blog post: How to Control Activated Sludge with Online Process Control) that relies on the development of a mixed culture of microorganisms to metabolize pollutants in wastewater. It was originally developed to remove organic pollution from municipal wastewater but has been proven for nutrient removal. Design innovations have produced configurations that can remove nitrogen and phosphorus. Dissolved oxygen (DO), sludge recirculation, and sludge wasting are the three controllable operating parameters once the aeration tanks and settling tanks are in the ground. Automation of DO control is presently the subject of intense interest because of the energy required for injecting it into the process. However, SRT, controlled through sludge wasting, is the single most important design and operating parameter affecting the performance of activated sludge systems (Metcalf & Eddy, 2004).
What is SRT in sludge?
Solids Retention Time (SRT) is a critical activated sludge design and operating parameter. The selection of an SRT has many consequences related to process performance, sludge production, and oxygen requirements. The traditional method for controlling SRT is to manually adjust the sludge wasting rate based on the food-to-microorganism (F/M) ratio or mixed liquor suspended solids (MLSS) concentration. The effectiveness of closed-loop control of SRT has been demonstrated in many locations.