 Today we will learn the topic water technology and a particular beat from the topic domestic treatment of water disinfection. This is the learning outcome for today's session. At the end of this session students will be able to describe one of the domestic treatment of water and students will be able to explain disinfection of water with suitable chemical reactions. This is the content we are going to learn in this session. First we will learn what do you mean by water quality parameters. Then we will learn what are the causes of infection in water, how water becomes infected and third we will see how infection from a water can be removed by using different disinfectants that is disinfection of water with chemical reactions. So first we will learn what are water quality parameters. Water quality is determined by physical, chemical and microbiological properties of water. These water quality characteristics throughout the world are characterized with wide variability. Therefore the quality of natural water sources used for different purposes should be established in terms of the specific water quality parameters that most affect the possible use of water. That is why the aim of this chapter is to provide an overview of water quality characteristics such as physical, chemical, microbiological and biological characteristics. First order the physical parameters of water which mainly includes pH, color, order, temperature and test. So water gets contaminated either by change in pH of the water, color of the water, it may acquire the objectionable order, it may acquire the temperature and it may acquire the objectionable test. So such kind of contamination of water is known as the physical parameters of water. It has been also suggested that the physical parameters of water can be learned at the site only because with due course of time there is a possibility of change in results of this parameter because pH, color, order, temperature and test may get affect with respect to time also. So the second type of parameter is known as the chemical parameters of water which mainly include acidity, alkalinity, chlorides, nitrates, dissolved oxygen, biological oxygen demand, chemical oxygen demand, oil and grease, hardness, metals, carcinogenic and hazardous chemicals, radioactive materials etc. So this is a big area, water gets contaminated with the help of varieties of chemical and then the water may acquire acidity, alkalinity, hardness, it may show the lower levels of the dissolved oxygen, it may become hard, it may become contaminated with the carcinogenic and hazardous chemical. So this is known as the chemical parameters of water which decides how the water become contaminated with the help of the varieties of chemical. And the third type is known as biological parameters of water which mainly includes varieties of microorganisms, bacterias, fungi and etc. Now how the biological parameter or how the biological causes are there, why water becomes contaminated with microorganisms, bacteria, fungi etc., what is the reason behind that and the reason is that when the water consist of a suitable quantity, a suitable and substantial quantity of organic type of waste such as oil, grease, cellulose, carbohydrates, proteins, fat etc. So such type of waste will act as a food for microorganism and in such circumstances inside that particular water, the several colonies of microorganisms grows tremendously. So these are the physical, chemical and biological parameters of water. Now particularly we will move to our point that is disinfection of water but before that we will go for learning you have to mean how the water becomes infected. So near about 80% of diseases are known as water bond diseases. Water becomes infected due to the discharge of organic type of waste coming from food, petroleum, pharmaceutical, agrochemical industries. Such industrial effluent is rich in fat, protein, carbohydrates etc. Therefore such organic type of waste will be a food for microorganisms and large number of microorganisms grow under such conditions. Thus contamination of water with varieties of microorganisms is known as infection of water. So what we have learnt here is how the good quality of water becomes infected and what is the cause behind that whenever certain organic compounds coming from different sources into a water resource that organic matter will act as a food and therefore large number of microorganisms grow in that particular water and that whole process is known as infection of water. Now here I would like to ask you one question which of the following type of waste causes infection of water? So it is a question which of the following type of waste causes infection of water? Option A carcinogenic and hazardous chemicals, option B oil and grease, option C organic type of waste and option D metallic type of waste. So think for a moment the correct answer is option C that is organic type of waste because organic type of waste will act as a food for microorganism and then that is the main cause how water becomes infected. Now we will come to our main point how to remove the infection from a water that is known as disinfection process of a water. The infected water causes several ill effects on human health. The effects varies from acute to chronic which depends on the type and concentration of infection of water. In order to maintain good quality of water it is needed to remove infection from water by using different disinfectants. So the process of destroying or killing the disease producing microorganisms from water and making it safe for mainly drinking purpose and other uses is called as disinfection of water. So what is this process? This process mainly includes killing the disease causing organisms from water and making it safe for mainly drinking purpose and other uses is known as disinfection of water. So first we will learn how the disinfection of water is carried out by using one of the disinfectant that is chlorine. Here we can use chlorine solution or we can use the chlorine gas. So the chlorine can be used directly as a gas or its concentrated solution. The chemical action of chlorine is production of hypochlorous acid and nation oxygen which kills the germs from water as shown in the below reaction. So see the reaction this is the infected water in which either we are passing the chlorine gas or we are adding the concentrated solution of chlorine and the reaction is that it form the HCl and hypochlorous acid that is very unstable. In next step what happen this hypochlorous acid molecule again dissociate in a molecule of HCl and the nation oxygen and we know that nation oxygen is a very active species of oxygen which kills the microorganism and it is known as the microorganisms oxidize and this is the process how we are doing the disinfection by using chlorine gas. Now here we will learn the second method that is disinfection of water by using chloramines. The monochloramine and dichloramine are used for disinfection of water. Chloramines are quite stable and do not impart any desegreeable taste or order to water. The hypochlorous acid and nation oxygen produced both are powerful germicide. The same we are shown with the help of reaction this is the monochloramine this is the infected water as a reaction it produces the ammonia gas and the hypochlorous acid which is unstable. In next step what happen this hypochlorous acid dissociate as HCl and the nation oxygen and nation oxygen is actively killing the microorganism. In this way the microorganism gets removed from the water. This is the second method we have learned which is carried out by using chloramines. Now the third one is that disinfection of water by using bleaching powder. After removing organic matter and suspended impurities water is mixed with adequate amount of bleaching powder and mixture is allowed to stand for several hours for the completion of following reaction. So this is the bleaching powder that is calcium hypochlorite that is a molecule which is mixed with the infected water which form calcium hydroxide and which evolve the chlorine gas. The evolved chlorine gas again react with the infected water it form the HCl and hypochlorous acid which is unstable molecule which in next step form the nation oxygen and the nation oxygen kills the microorganism and this is also one of the effective method for removing the infection of a water. So here we have learned the three method one is disinfection of water by using chlorine gas or concentrated solution second by using chloramines and third by using bleaching powder. Now how this process is called carried out and the process is carried out by using a chlorinator. Water and adequate quantity of suitable disinfectant is added from the top of the chlorinator during their downward journey through the tower it get mixed thoroughly with infected water. The waste water is kept with disinfectant for several hours to complete disinfection process. Then the treated water is taken out from the outlet at the bottom generally for moderately infected water 0.3 to 0.5 ppm of chlorinated compound is adequate. Disinfection of water is carried out by using chlorinator as shown in below figure. So this is the simple figure this is a container in which the provision of mixer is there to mix the content from one end we are taking the chlorinated compound from another end we are taking the infected water. Here the reactions occur and then we are taking out treated water and then it is collected in one big tank it is stored there and the killed organisms floats on the surface of the water which can be removed with the help of the scrappers. What are the advantages of disinfection? It is effective and economical it requires very little space for storage it can be used at low and high temperature and no salt impurities are incorporated in the treated water. Now what are the disadvantages of this process? Access of chlorine may cause the unpleasant taste and odor and excess of chlorine may cause irritation to the mucous membrane. So these are the two disadvantages of this process and these are mainly related with the quantity of the chlorinated compound. All these slides are prepared by using a textbook of engineering chemistry written by Jain and Jain thank you.