 Welcome back to a new session on dentistry and more. So today we have a water purification on a large scale and small scale. So we know how we drink water on a out setup if we don't have a well or above well setup. We depend on the municipal or corporation water supply. So how we get this from municipal water supply means we get a pipe connection or there will be a centralized pipe connection which goes through every lane or every road and it goes to the every house thereby we get water. So it is very important to maintain the quality of water because it is a centralized supply if anything goes wrong it will affect a lot of people. So let's see how a large scale water is getting purified. So commonly if we have a centralized supply the first process will be purification of water. So let's see in detail about the purification of water on a large scale. So we know there is no water, no life, no blue, no green and we have a water pollution low which was came into existence in 1974. So that was just part of introduction. So today we are seeing both large scale and small scale. So small scale is a very simple household purification or disinfection of well. But the important one, the complex, the more laborious thing is large scale water purification. It has basically three steps that is the storage, second one the filtration and the third part is disinfection. So the storage part is like we collect water from the river or a lake or any common sources we collect through pipe system and we collect at a common area where this water is getting purified or we say water treatment plant. The second part is filtration. So we have two types of filters that is slow sand filters and rapid sand filters. Slow sand filters where primitive types nowadays it is not commonly used because it needs a large area. It requires a very large area because it is working by a principle of biological action. We don't add any chemicals in slow sand filters. So the gravity type action is having filters through the water bed or the filter bed and get purified. So it requires a very large amount of area because we are dealing with water purification for a very big population. So nowadays we use rapid sand filters that involves chemical actions because it doesn't need a storage. Basically this storage works with slow sand filters and rapid sand there is no need of storage. We can directly treat the raw water from the river or lake or pond or whatever. So nowadays rapid sand filters are very common because it can work 24 7 but slow sand filters need to be stopped once the filter bed is clogged or if it loses its efficiency. And the last part is disinfection we usually do with chlorine. So let's see what is small scale purification will deal it later. That is like boiling chemical disinfection using bleaching powder or chlorine or HTH tablets add in potassium per magnet and how to disinfect a well that is by using bleaching powder and double port method. This commonly we do at our house. So let's see about storage. So storage we can use a natural or artificial reservoirs. So what is the effect of storage? It has physical chemical and biological action. Physical means 90% of its impurities will be settled. There will be oxidizing action and biological the 10% of bacteria remains at the end of one week. But the optimum period is two weeks. If we keep more than two weeks there will be production of algae. So that will be a problem. So maximum we can keep it for two weeks. So it is commonly seen in biological filters. So the first part is storage. So now we are moving to filtration. Okay, so how water is getting filtered filter. We have slow sand and rapid sand. This is biological and mechanical. So slow sand filters are started in 19th century in Scotland. So basically it has a filter box and a filter control valves. Filter box has supernatant water, sand pit and under drainage system. Looks like this. This is a filter box, a cross-sectional or diagrammatic picture. So there is raw water inlet. So water goes through here. So this is biological air or schmutz-tec formation. So water will be here and it will get filtered through here. This is a sand pit and there will be filter controlling valves at the bottom. So it goes out through here. Okay, so this is a diagrammatic representation of biological filters. So this is a vital part schmutz-tec or biological air. So it forms biologically. We are not creating it. Once the sand pit is laid, it forms automatically at one or two weeks. So that biological air is the part which actually do the filtration process. Okay, so this is what I was saying. It needs a very large area. You can see how big it is, the slow sand or biological filters. So it needs very big area. So each one is a filter bed. So it has a filter bed. Yes, you can see this is a water filter bed. All these were similar ones. So these sands were like after a few weeks, it will go useless. So we need to remove the top layer of the sand and we need to replace it with new sand. Then we have to keep it for one or two weeks to get formation of that particular biological or zoogli layer. So we need to have many similar types at the same time because once efficiency is lost, we need to drain the water and we need to replace the sand bed. But water has to be filtered because it has to go for the central supply and to houses. So we need to keep many similar plants at the same time. So it requires very large area. But in rapid sand, there is no need of storage or this type of big land area. So let's see more detail about the, filter bed or the biological filters. There is a water, there is sand bed, then there will be gravels. There is perforated pipes through which the water is collected and it goes to the main central supply. So it is a cross section. The top layer will be very minute sand, then there will be co-sat, then there will be fine gravel and there will be co-scrable and between these pipes. So since it is a cross section, it looked like this. So water collected through these pipes to the outer. Okay, so we have supernatant water, sand bed, under drainage system and walls. So these are the four components of a filter bed. So this is, I was talking about after a period of time, this entire plant will go useless because it loses its efficiency. This, the heaps of sand, what you're seeing is the top layer of unused or the not used plants because after a while it loses its efficiency. So what we do is we scrape off the top layer and remove it off because it was biological layer and it can't be used for a very long time. So after few weeks it has to be replaced because it loses its efficiency. So meanwhile you have to drain the water and you have to keep, remove this and you have to keep in new sand because it already loses its height. So we have to add new sand and wait for this top layer to become biological layer because it forms biological layer by growing algae and plankton over it. So that acts as a filter in biological filters. So basically the supernatant water will be one to 1.5 meter. So this is a waterless plant. So this is a water plant. So I was talking about this height. If water was there, how would it be look like? So this is 1.15 meter. Then it is always promotes water to the downward direction and there will be a waiting time of three to 12 hours for water undergo partial purification by sedimentation and oxidation. So there will be three to 12 hours. The water will be there three to 12 hours for actual or a good purification if good purification to happen. So what happens in the sand that is the sedimentation and mechanical straining. The supernatant water act as a settling reservoir and settleable particles sink to the sand surface, this part, then mechanical straining. Particles too big to pass through the gap between the sand grains are retained. So it will be retained here. So this filter is known as biological because there will be a formation of slimy gelatinous layer over the sand bit, which contains algae, bacteria and atoms and that is known as zooglial, vital or schmutz take layer or biological layer. So that is the part which actually does the filtration. There is no chemical we are adding. We are just using biological action of this water and sand reaction. So we know we keep a sand in a water for a while. There'll be algae formation over the top layer of sand. The same principle is applied for here for the purification of water. So this is known as heart of the slow sand filter. So there'll be a formation of white layer if we keep water for a period of time. So these particles will be retained by this biological layer which removes organic matter and holds back bacteria and also oxidizes ammoniacal nitrogen into nitrates. So this is the vital part or the most important part in slow sand filter or the biological sand filter. So the filtration and storage is most vital part in slow sand filter. So storage is not very important in rapid sand filter. So I'll explain you. So this is known as schmutz take or vital layer or biological layer. So there'll be under drainage system. So which is very shorter that is 0.15 meter. It is always at the bottom of filter bed. So this is under drainage system. So through this, the water drained and goes to the central supply. There'll be porous pipe which I shown just now and rate of filtration is 0.1 to 0.4. There'll be walls to regulate the flow of water. We can control the outlet of water after the purification. Then we need to do the filter cleaning. That is, that was I was showing this picture. This is a filter cleaning process, okay? So in slow sand filters, filter cleaning is done by a process known as scraping. So we know what is scraping. So we scrape off the top layer once it becomes useless. Okay, so filter cleaning. If the bed resistance is very high, then we need to open the walls fully, drain the water and scrape the top portion of sand up to two centimeter depth. Then we need to replace it. So after three to four years, new filter bed is constructed. So this picture you can see, this is after three to four years of usage. We remove this two to three centimeter of top layer. Then we keep a new layer for the next usage. So advantages is very effective. It is the most effective compared to the rapid sand. And simple to construct, there is no chemical action. There is no need of energy or electrical or other forms of energy. We need to just wait for the purification process. Construction is basically cheaper, but it requires very large area. Next, we see the rapid sand filters. So that is the most commonly used. And there are two types. It started in USA 1885. Gravity or open type and use type, pressure type, potassium and candies. So this is how it look like if the water is drained completely. This part is a filter part. So this is a structure of, for a flow diagram of this rapid sand filter. So first, there's no storage. If we are storage or we are taking with the raw water, we need to mix it with alum or coagulant. So there'll be first process is rapid mixing for 30 seconds. Then there'll be flocculation for 15 to 30 minutes. Then we keep it for sedimentation one to four minutes. So there'll be coagulant, it will be settled. Then we send it for filtration, then disinfection. Okay, so this part is much more complicated than rapid sand, storage, raw sand. There was no coagulant, it was only gravity action. Here we act, coagulant act as a first part of purification because all the particles will be coagulated because we are adding a coagulant. It becomes floc after flocculation. It is a slow circling or slow rotation of the paddles which causes flocc formation and flocc will be sedimented. So a part of purification is done here because we are doing it a very rapid phase. We need to pump it for a very shorter period. We can't wait for a very longer time. We have no waiting time. Usually in slow sand, there is three tutorials waiting hour. Here is there is no waiting hour. We just wait for 15 to 30 minutes rapid mixing 30 seconds, 15 minutes or 30 minutes flocculation then max one for sedimentation. There it was 10 hours waiting period was there. So here it is done very fastly. Then we remove the coagulants then we send it for filtration. Filtration bed is same as what we seen earlier. Only thing is it is just mechanical straining. There is no biological layer formation because already most of the particles and impurities, bacteria is already removed at this process. So here the part of filtration is done at filter table. So rapid sand filter is almost similar as our slow sand. Only thing is it is working at a very slow, sorry, very shorter period of time. And really there is no need for really big land. Can do it at a very close space or a shorter space. So this was the first part aeration. So first part the raw water from the river or on will be done a process of aeration. So it will get oxidized. So the first step was coagulation. So we add alum to the water by five to 40 milligram per liter. So you can see this process coagulation. So coagulant will be added. So there will be rapid mixing. That is in mixing chamber, violent mixing will be done. So this coagulant will be coagulating the impurities. So it becomes flow and it will be settled or sedimented. So that is known as flocculation. So after this rapid mixing, so it will be sent to the flocculation chamber. So there will be slow stirring of water by paddles maybe for 30 minutes. So flocculant alumina hydroxide, what it does is it entangles all particulate suspended matter along with bacteria. Then it will be sedimented at the sedimentation chamber and it will be removed. So that was a difference between biological and rapid sand filters because this process was not there in rapid sand filters. So the next part was filtration. Okay, so the first part was absent in rapid slow sand, the flocculation sedimentation coagulation, rapid mixing, flocculation was not there. Sedimentation was there, but it was along with the filtration, but here it was separate. So after sedimentation, we sent this water to filtration bed. In slow sand, it was all along in a simple chamber where the sedimentation and filtration happens. So filtration is like filter bit, how we seen the slow sand. The difference I have a one table in next slides. So there'll be sand particle 0.4 to 0.7, graded gravel 30 to 40 centimeter, then there'll be one to 1.5 water on the top and rate of filtration, this is 5 to 15. And remaining alum flocs from a slimy layer over sand bit, it holds back the bacteria, oxidizes, organic matter. So this alum floc will be there. So it act as a very slimy layer over the sand bit. So it act as a filter unit or you can say similar to the biological layer, but actually it is a mechanical process, mechanical straining happening, but still there'll be a alum floc over the sand bit. So the scraping process was done in slow sand filters for cleaning the bed once its efficiency is lost, but the back washing is done in rapid sand filters. So what is back washing? So it is by air bubbles or water. He's pumped in a reverse direction from the under. When floc layer becomes very thick and about 15 minutes. So if the floc layer, the alum floc layer over the top becomes very thick so that it holds back the water, it is no longer doing the filtration. What we have to do is we have to remove it. So how we remove it? We pump air or water, mostly air from underneath so that it creates pressure and the top layer will be outflowed and it removes the, all of this alum floc. So it takes maybe 15 minutes, but you can see the slow sand filtration, we have to remove the entire big area. So we need to rebuild it. We need to recreate a sand bit. We need to put new sand and wait for it to become biological air. So this is a very simple process. We can do back washing in 15 minutes. So this is a cross section we already seen. So advantages is the fastness is very fast actually. You can do the raw water directly. There is no need of storage. The filter bed occupy very less space compared to the big land area which requires for the slow sand. Filtration is almost 40 to 50 times faster than slow sand filter. And washing of the filter is very, very easy compared to the slow sand there. It was scraping and a lot of replacement. Here it is only 15 minutes of back washing and there is more flexibility. So just compare the slow and rapid sand area, rapid sand very lateral space, very large area. The rate of filtration is very high 200 where it is just two to three. Sand size was 0.4 to 0.7. It is lesser. Retreatment in rapid sand we need coagulant. We need to sediment it first before treating it to filter bed. But there is only sedimentation happening in the slow sand because it is totally biological action. Filter cleaning here we have seen back washing through air or water. Here it is scraping. Operation we need more workers, more energy, more people because it requires more skill adding of alum operating this back washing because it is less skilled. Once it starts it will go like that. Only thing after two to three years we need to remove the sand bed or scraping of sand bed. Removal of color is very good in rapid. It was better. Slow sand was actually better. Removal of bacteria was good in slow sand compared to rapid sand. This was a summary of the slow and rapid sand filters. So I can just show you the comparison here. There is only biological layer but here you can see there is coagulant flocculation. Then sedimentation is there both places. But this spot is not there in conventional slow sand because this is the part where the purities are removed. And also filtration is also there. So next part is disinfection that was the last part. So disinfection usually done by chlorine. So why we are doing disinfection? Like what are the criterias that is, should not be influenced from properties of water within short time, should not be toxic and color imparting or leave water importable. Importable means drinkable. Should be available cheap and easy to use. There should not be any residual concentration to deal with contamination. Easily detectable. Simple techniques. So what chlorination is done? It kill pathogenic bacteria, oxidizes iron, reduces taste order, controls algae. So these are the actions. Water and chlorine it become hypochlorate and hydrochloric acid. So hypochlorate it will become H plus and this ion. And this ammonia is combined with chlorine. So this chemical reactions happen when we add chlorine to the water. So these are the principles of chlorination. Water should be clear, free from turbidity. And we need to find out the chlorine demand that is how much chlorine is needed to destroy the bacteria or organizing, sorry, organic matter and to neutralize ammonia. So free residual chlorine for a contact period of one hour we need to keep. And there is a break point that is a point when chlorine demand of water is met and free residual chlorine appears. So if we take one liter of water, we keep adding chlorine at one point of time because we keep on adding chlorine so it will get dissolved at one point of time it will start appearing because it dissolved completely. The remaining portion will be become residual chlorine. So that point is break point chlorine. So principle of break point chlorine is to add sufficient chlorine so that there should be a 0.5 milligram per every liter free residual chlorine should be present in water. So that means if it is very contaminated the break point chlorination will be high. If one liter of water we take and we add two milligram per liter of chlorine and another very contaminated water it might require maybe five milligram per liter. It depends on the contamination of water. Okay, so finally we have to decide the dose of chlorine that is chlorine demand plus free residual chlorine. The chlorine demand is the break point chlorination at the amount of chlorine where this free residual chlorine appears. So minimum recommended concentration of free chlorine is 0.5 milligram per liter for one hour. So that amount of free chlorine should be present. So how to calculate it? It's suppose if we are taking one liter we add two milligram per liter so it start showing free residual chlorine. So we add a 0.5 milligram per liter so it retains 0.5 milligram. If it is very contaminated five or six or seven it will be dissolved. So we add a 0.5 milligram per liter extra. So this 0.5 milligram per liter will be there for the chlorination action or the disinfection. So we can use it by chlorine gas, chloramine or perchlorone. So commonly used chlorine gas. So how do we do a small scale water purification we can do boiling chlorine tablets add in potassium permanganate. So well cleaning by two methods that is one adding bleaching border. So how much bleaching border we should add then we can calculate with this pi D square H by four. This D is the diameter of the well achieves the depth of the water and pi 3.14 and we can calculate it. So that much amount we need to add. So double port method was a simple method invented by NERY that is National Engineering Environmental Engineering Research Institute in Nagpur. So the same institute who developed our Nalgonda Technique for Fluorine Deflugation. So we keep a cylindrical board there will be two boards. So one port will be inside and one port will be outside the smaller port will be this much dimension that is height 28 centimeter and diameter 16 centimeter and all at the upper portion. So what we mix we keep one kilogram bleaching border and two kilogram co-sand and the bigger one will be having a height 30 centimeter diameter 25 centimeter all at the lower portion. Okay, so this will be immersed in the well and we keep when we do disinfect of a well. So this is repeat after every three weeks this is known as double port because it has two ports. So that's all about water purification. The basic difference between slow and rapid sun was important. In slow sun there was no chemical we are adding it was biologically happening with the formation of a biological air sedimentation was there and biological action. So water is getting filtered but whereas in rapid sun filters there'll be a chemical alum we adding we do it does the coagulation and flocculation so flocs will be removed that was a part of filtration and again it will go to the filtration bit. So that's all about purification of water on a large scale and a small scale. The important part was rapid sun and slow sun and this principles of chlorination like dose of chlorine how much chlorine we need to add that is chlorine demand. That is a break point chlorination the point at which the residual chlorine appears. So always we should have a 0.5 milligram per liter of residual chlorine per hour contact time for a water we should say if it is portable. So this is the mechanism of portable water portable means drinkable without drinkable water without any pathogens. So that's all about water purification. I'll come up with a new session on dentistry and more. Thank you.