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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 return activated sludge?
Return Activated Sludge (RAS) – The settled activated sludge (biomass) that is collected in a secondary clarifier and returned to the secondary treatment process to mix with incoming wastewater. This returns a concentrated population of microorganisms back into the aeration basin.
What is the purpose of activated sludge?
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.
What are the advantages of recycle sludge to aeration tank?
Advantages of Activated Sludge Process Low installation cost. Good quality effluent. Low land requirement. Loss of head is small. Freedom from fly and odor nuisance high degree of treatment.
What is complete mix activated sludge?
Complete mixing activated sludge systems are those activated sludge systems where the incoming wastes are uniformly mixed with the activated sludge to maintain all suspended solids in suspension with a uniform oxygen uptake rate throughout the entire aeration tank and a mini- mum dissolved oxygen concentration of 0.5
How does a sludge judge work?
The sampling device enables you to take accurate readings on settled solids in a variety of liquids, to any depth. Lower the Sludge Judge to the bottom of the tank. When the bottom has been reached and the pipe has filled to the surface level, tug slightly on the rope as the unit is raised.
How do you remove sludge from water?
Dewatering aims to reduce the water content further so that the solids content of the sludge remains about 20 %. It can then be handled like a solid material. Dewatering can either be done mechanically using a filter press or by using drying beds. Sludge drying beds, however, provide the simplest method of dewatering.
How is sludge treated?
Many sludges are treated using a variety of digestion techniques, the purpose of which is to reduce the amount of organic matter and the number of disease-causing microorganisms present in the solids. The most common treatment options include anaerobic digestion, aerobic digestion, and composting.
Is provided after activated sludge process?
The combination of wastewater and biological mass is commonly known as mixed liquor. In all activated sludge plants, once the wastewater has received sufficient treatment, excess mixed liquor is discharged into settling tanks and the treated supernatant is run off to undergo further treatment before discharge.
What is not required in the activated sludge process?
3. What is required to keep the activated sludge suspended? Explanation: To maintain the aerobic conditions and to keep the activated sludge suspended, a continuous and well-timed supply of oxygen is required. Flocs of bacteria, which are suspended and mixed with wastewater is used for the process.
How do you determine sludge age?
The sludge age of an activated sludge process can be calculated by dividing the pounds of suspended solids or MLSS in the aeration tanks by the pounds of suspended solids that enter the aeration tanks (Equation I.
What are the steps of activated sludge process?
The sludge treatment process involves four steps as described here.Treatment Steps Step 1: Screening and Pumping. Step 2: Grit Removal. Step 3: Primary Settling. Step 4: Aeration / Activated Sludge. Step 5: Secondary Settling. Step 6: Filtration. Step 7: Disinfection. Step 8: Oxygen Uptake.
What happens to sewage sludge?
Sewage sludge is a product of wastewater treatment. Once treated, sewage sludge is then dried and added to a landfill, applied to agricultural cropland as fertilizer, or bagged with other materials and marketed as “biosolid compost” for use in agriculture and landscaping.
What is the substrate for the activated sludge process?
Active sludge is the sum of the remaining substrate(organic + inorganic)(soluble + insoluble) plus the viable microorganisms(active biomass), plus non viable microorganism(inactive biomass) product of the microorganisms lysis and other species, like phytoplankton.
Which is used to remove sludge?
Dewatering decreases sludge liquid volume as much as 90 percent. Digested sludge is put through large centrifuges that work in the same fashion as a washing machine spin cycle. The spinning centrifuge produces a force that separates the majority of the water from the sludge solid, creating a biosolid substance.
How can you improve settling in activated sludge?
Excess organic load can be remedied by reducing the waste-activated sludge rate by an amount less than 10 percent per day, to return to proper loading parameters and increase the returned activated sludge rates. About a 30 percent level of settled solids in the clarifier should be established and maintained.
How does activated sludge appear?
In activated sludge process wastewater containing organic matter is aerated in an aeration basin in which micro-organisms metabolize the suspended and soluble organic matter. A part of this settled biomass, described as activated sludge is returned to the aeration tank and the remaining forms waste or excess sludge.
Which are the three ingredient in activated sludge system?
Which are the three ingredients in activated sludge systems? Explanation: The cells need oxygen for their metabolism, air is injected from the bottom of the aerator. The water is well agitated by the rising bubbles and creates good contact between the three ingredients: cells, sewage and oxygen.
How does a return activated sludge plant work?
The activated sludge is aerated to dissolve oxygen which allows the organic matter (BOD) to be utilised by the bugs. The organic matter, or food, sticks to the activated sludge. The oxygen dissolved in the water allows the bugs to use the food (BOD) and also to change the ammonia to nitrate.
What is required to keep the activated sludge?
To maintain aerobic conditions and to keep the activated sludge suspended, a continuous and well-timed supply of oxygen is required. It consists of flocs of bacteria, which are suspended and mixed with wastewater in an aerated tank.
Which is the first step in the sludge treatment process?
Thickening is usually the first step in sludge treatment because it is impractical to handle thin sludge, a slurry of solids suspended in water. Thickening is usually accomplished in a tank called a gravity thickener. A thickener can reduce the total volume of sludge to less than half the original volume.
