 Greetings students, my name is Mahiro Balai, I am an assistant professor in civil department WIT, Sallapur. Today we are going to learn about the topic that is duckweed ponds. So what is the learning outcome? At the end of the session, student will be able to understand the concept of duckweed ponds. Basically, duckweed ponds are the system in which lot of duckweed is present inside that lake. Okay? So duckweed is a tiny floating plant. If you see, if you can see in the picture, they are the small plants which are continuously floating on the pond. It usually grows on the surface of ponds or lakes in a or in a slow moving streams. Duckweed can easily multiply very much rapidly and form the lush carpet on the top of the water. Duckweed is a favorite food for ducks, which is how it got its name. That is duckweed. Fish and snails eat duckweed too. So healthy duckweed is having a bright yellow-green color. It is an unusual plant because it has no leaves or stems. Instead, it is having the leaf-like fronts that are attached at the center. From each front, the single root hangs down. If you can see on the diagram in the overhead view, that is the plant, you will get to understand the plants are having kind of a front-like leaves. If the production goes on, if the increase of duckweed starts to happen, small bud fronts is also going to be coming out from the fronts. If you look at the side view, you will get to understand every leaf or every front is having a separate root. That is continuously inside the water. Duckweed birds to form new fronts. Each front grows its own root and it becomes an independent plant. There are various types of duckweeds which are present in the pond. They are typically small, fragile and free-floating aquatic plants. There are total four types of genera. First one is Sparadella. Second one is Lamna, which is mostly used for the treatment of waste water. Third one is Wolfea. And the fourth one is Wolfeala. So basically, lamnacea family that is a part of lamna is a worldwide but most diverse species appear in the subtropical or tropical areas. Another condition for which the duckweed grows is always between 6 to 33 degree Celsius. Water having the pH in which the duckweed survives should be in between 5 to 9. But it can easily grow at a faster rate when the pH is having the temperature range of 6.5 to 7.5. So how the duckweed ponds are usually used for the treatment of waste water? If you can see, this is the duckweed pond or this is a cylindrical shaped duckweed pond in which the upper layer is continuously in aerobic. Why I am saying it is in aerobic? Because it is continuously exposed to atmosphere and also sunlight. By which large amount of oxygen can come inside that pond. So we can say the upper 10 cm thick layer of the pond is always in the aerobic. In that what is going to happen when the waste water is coming inside that treatment unit or in that cylindrical pond easily whatever the duckweed ponds which have been grown on the upper layer of the pond they will easily take whatever the carbon dioxide which is present in the atmosphere and they will throw out large amount of oxygen inside that pond. So it will automatically large amount of surface aeration and carbon dioxide is also made to push inside the pond. The carbon dioxide is converted by the duckweed mat which is the mat of continuous duckweed plants and the oxygen is made to come in. In this way large amount of oxygen is made to pass inside the treatment unit. Using that treatment unit large amount of bacteria which are present in that pond or in that waste water will start to grow. And automatically bacteria are exposed to lot of oxygen and lot of organic matter is present in the waste water so easily they will degrade the organic matter and easily the decomposition of organic matter take place. Using that large amount of chances of formation of algae is also can be there because algae needs lot of carbon dioxide, they need lot of oxygen and they need lot of sunlight. So automatically on the upper layer of the duckweed pond there are chances algae can easily form. When the algae is also going to useful for the decomposition of organic matter they are also going to throw out the dead cells or suspended solids that is what we need. In typical biological treatment units what we say the dead cells are basically sludge but the duckweed ponds the dead cells are also kind of a sludge only. So this upper layer is always acting as a aerobic. Now at the bottom of the aerobic zone you will get to understand very less amount of oxygen will be there. So whatever the organic nitrogen which is present in the waste water is made to eaten up by the bacteria as they are getting a lot of content of bacterial culture which has been formed out in the aerobic zone. These type of bacteria will eat out the organic nitrogen and they will throw out the ammonium and phosphate contents. These ammonium or phosphate contents can be converted into the nitrates or nitrates and they will go out or that that can be also be taken up by duckweed ponds. Similarly the phosphates can also be eaten up by the aerobic bacteria and automatically the dead cells can be formed. So in this fashion the nitrates and phosphates can go above the anoxic zone. If that ammonium or phosphate is still remaining in the anoxic zone they will be converted by the nitrates with the help of oxygen which is given out by the duckweed ponds or it is coming through the aerobic zone. So automatically that nitrates again they will convert to the nitrates using the same oxygen and that nitrates will be converted into the nitrogen gas. And that nitrogen gas which is having a very much lesser density will be go out. In this fashion the anoxic zone is typically used to treat the organic nitrogen and the phosphates. The next one is anaerobic zone. If you can see at the bottom this is the anaerobic zone in which whatever the organic waste which is still remaining in the wastewater that will be converted into the organic acids and that organic acids will be eaten up by anaerobic bacteria with the help of bacterial formation, then acetogenesis, then acetogenesis and then methanogenesis. So in this fashion the organic acids will be converted into carbon dioxide, it will be converted into the ammonia, it will be converted into the sulphide gas and large amount of methane. As these kind of gases are very much lesser in density they will be again exposed and taken out from the duckweed ponds. So in this fashion all type of treatment will be done in the duckweed ponds. So in the duckweed ponds what is going to happen with respect to various types of pollutant removals. The phosphorus removal, the plant uptake and sedimentation are quantitatively relevant for phosphorus removal in duckweed systems. Talking about the organic matter and BOD removal, BOD is aerobically digested by microorganisms attached to duckweed fronds. Anaerobic processes are responsible for BOD removal in the sediment that is at the downside. How the nitrogen removal is going to happen? Besides the plant uptake, denitrification and volatization of ammonia are quantitatively relevant processes for nitrogen removal in the duckweed system. TSS are majorly extend removed by the sedimentation. A minor fraction is adsorbed on the roots of the fronds where the microorganisms degrade apart and a part of the degraded product is made to assimilate at the bottom of the plants. How the pathogens can be removed? Basically pathogen removal takes place through natural die off. It means whatever the pathogens or whatever the harmful bacteria which are present in the duckweed, they are exposed and they are made open and they can directly die themselves naturally. Therefore, long detention time is necessary for the duckweed ponds. How toxins can be removed? Basically toxins are the lypophilic that is hydrophilic get greatly accumulated in the lipids of the cell membrane from where they are exerted to the inner side of the lamanance cell. So let us see the advantages. Typically traditional rudimentary and it is easy to implement and it is very much ideal for the rural areas. Duckweed ponds are also easy to build. See it is very much simple to operate and it requires very much little or no maintenance. It also requires relatively smaller land areas. It also reduces the nutrition contamination of natural systems. Heavy materials can also be absorbed by the plants and they are not returned back to the water which is very much good part. Duckweed based ponds are basically produces plant biomass that can be used as a fertilizer also. Even aluminum filled supplement can be also one of the advantage of duckweed plants and that can also be the source of methane. Duckweed also produces more protein per square meter than soybeans. Duckweed is easier to harvest than algae or other aquatic plants. So let us have few review questions. Duckweed is a dash plant. It is whether it is floating or submerged or both A and B or none of the above. In duckweed ponds pathogens can be removed if long detention time is provided whether this statement is true or false. Following nutrients can be removed by duckweed ponds, phosphorus, BOD, toxic materials or all of the above. So let us see their answers. Duckweed is always a floating plant. In a duckweed ponds pathogens are always removed if long detention time is given. Lot of nutrients can be removed in the duckweed ponds which we had seen earlier in which phosphorus is there, BOD is there and toxic materials are also there. These are the references I have used to make this video. Thank you.