 Good morning friends, my name is Mahirubali, I am an assistant professor in WIT. We are today going to study about activated sludge process, so let's begin. So in this session, we are going to learn about the concept of activated sludge process in wastewater treatment plant. So where do we stand till now? We had completed the primary sedimentation tank in the flow sheet of wastewater treatment plant. Now we are going to study about the secondary treatment of wastewater. Now we have to focus on the carbonaceous, the nitrogenous part of wastewater. So in the secondary treatment plant which involves aeration and clarification, we will remove all this carbonaceous matter or biological matter which are present in wastewater in this secondary plant. So the activated sludge process is basically a part of secondary treatment plant. Now what is activated sludge process? Basically activated sludge process is a suspended growth biological treatment. It means that whatever the biological matter which is present in the wastewater will be in the suspension form in the secondary plant. Now how we can treat that non-carbonaceous matter? Basically we add some microorganisms which are aerobic or facultative in nature. Now aerobic means the microorganisms require oxygen for their own growth. And what is facultative means? Those microorganisms which can be sustained themselves with or without oxygen. Now these microorganisms will stabilize the material in wastewater. Now what basically they will do? Microorganisms basically consume the organic matter from the wastewater using oxygen for respiration. Mostly we use aerobic microorganisms for activated sludge process. So if you see in this diagram the microorganisms consume oxygen to take up this food and reproduce themselves, sustain themselves, grow into themselves. So let's see at which stage we mostly use activated sludge process. So before that we have to understand if we are putting microorganisms at food. Food means basically the carbonaceous matter which are present in the wastewater. If we are putting in the secondary clarifier or secondary treatment plant what should be the growth of microorganisms and how the food or the MLSS or the carbonaceous matter going to decline. So what we study? We study about growth phases of biological system. In which we take a graph of growth rate of food and microorganisms with respect to time. So with respect to time how they are going to grow or how they are going to decline. So first in the plant or in a typical plant food is always present in abundant. And the microorganisms which we have added are very much small. Okay, such phase we call it as lack growth. It means the microorganisms will just start to increase themselves by taking a lot of food which is present in the plant. Now in the secondary what will happen slowly slowly the food is going to decline. Why? Because these food will be consumed by microorganisms and simultaneously the growth of microorganisms will increase very much faster. Such kind of a phase we will call it as log growth. Fine. Now what will happen after that? There will be a time when the microorganisms will be at a higher stage, at the peak stage. And the food will be at a very much lower stage, a relatively lower stage. At such condition microorganisms, content of microorganisms will be very much higher relative to food. So there will be a very much lesser food available at the time where the microorganism content is too much higher. Such kind of a phase we will call it as declining growth. Why declining growth? Because after a peak stage both the food and the microorganisms are going to decline. They are going to reduce. What will happen after that? As the food is simultaneously going to decrease the microorganisms will also start to decrease. Now we have to understand for their own survival what they will do? They will start to eat themselves. Because there is a very lack of food present in the plant. So at that particular time what will happen? From this stage they will start to eat themselves. So there will be a higher reduction of microorganisms in the plant. So what will happen? Whatever the microorganisms which are sustained themselves by eating to each other, they will be very much active in their own. What does it mean? If you assume that in a particular room if any organism is present and he is too much hungry. What will happen? He will start to eat whatever present in that room. It means that he is very much activated. He can eat anything whatever he is given to. So whatever the organisms which are present at this stage are highly activated. What we do? We use these organisms in our activated sludge process. And these overall growth of microorganisms we will call it as endogenous respiration or endogenous growth. Now let us study how the flow sheet of activated sludge process is present. There are total two plants in activated sludge process. One is biological reactor or in simple words we say aeration tank. And the second one is secondary clarifier or the sedimentation tank. What will happen first? The influent will come into the aeration tank or the biological reactor. Here what we do? We put a lot of aeration pipes at the bottom of the tank. And we use aeration for proper mixing of whatever the influent which is coming and the organisms which are present. And they are highly facultative or they require oxygen. They will take this oxygen from this aeration and they will grow themselves. As the influent is containing a lot of BOD or the carbonaceous matter. So food oxygen is highly present in this tank. So the microorganisms will take oxygen and food and they will reproduce themselves. After all the aeration these microorganisms will come into this sedimentation tank. And flocculation and sedimentation happen simultaneously. What happens? Whatever the sludge which has been collected or settled down in the sedimentation tank is taken. And of some proportion of this sludge is again mixed with the influent and is taken back. If we had remember in the earlier slide we use activated sludge. So here all this sludge is happening is the activated sludge. How it is happening? How what is the mechanism? We will see in the next slide. But first we have to understand the some portion of the sludge is mixed with the influent and again taken back to aeration tank. And the surplus amount of sludge is taken out from whole this system. So whatever the effluent or whatever the clean water which is present above the sedimentation tank is taken out as a effluent. Okay it's very much simple. Now let's see what is the mechanism how it is happening. First in the in this aeration tank the influent is adding MLSS which is carbonaceous matter and microorganisms. And mostly microorganisms that is MLSS and MLVSS. This is oxygen is present because we are providing aeration into it. And the organic material in the form of carbonaceous or phosphates or nitrogenous material which are present in the wastewater. What happen? They will react and new microorganisms will reproduce and simultaneously carbon dioxide is also removed off. In the with carbon dioxide there is ammonia, there is a hydro gas, there is S2S gas which is also coming out. Okay so all the hazardous gases are also getting removed by this process. Now what will happen? These microorganisms will come into the secondary clarifier and these microorganisms will start to eat each other and the endogenous respiration will happen. When this process is going up the carbon dioxide is also getting evolved and whatever the oxygen which are required by these organisms will be taken up by the atmosphere. Okay and after the endogenous respiration the activated sludge will produce. Why we are calling activated sludge? Because they are highly activated microorganisms which are ready to eat anything. Some of the activated sludge will be taken again and added and the MLSS will be created and the surplus sludge will be taken out. Now let's see review questions. First is ASP is a suspended growth process. True or false? ASP works with the biological growth phase. In which biological growth phase ASP is working? Black phase, endogenous growth phase, log phase, decline phase. Third one is MLSS is maintained in the aeration tank by adding activated sludge, carbonaceous matter present in the influent, both A and B or none of the above. Let's see the answers. ASP is always a suspended growth process. The carbonaceous matter which are present in the wastewater are always in the suspension form. ASP is always worked in endogenous growth phase. And the third one is MLSS is maintained in aeration tank by activated sludge also and carbonaceous matter present in the influent also. So this whole PPT taking by reference of Metcalphate D, B.C. Panmyan, P.V. Rubo. Thank you.