Need of water
We need water to survive on this planet. Water is an important and necessary component. It is absolutely necessary for the body's various metabolic processes and for the production of hemoglobin.
One gallon per person per day is sufficient for drinking and cooking. A bullock, mule, or horse can consume approximately 11 gallons at once. Standing up, a man should have an average of 5 gallons, while a horse or camel should have 10 gallons. An elephant consumes 25 gallons, a mule or ox consumes 6-8 gallons, and a sheep or pig consumes 6-8 pints. These are the bare necessities.
6 gallons (or 10 pounds) of water are contained in one cubic foot.
Water must be purified and supplied in a systematic and orderly manner to meet such a large demand.
However, as the world's population has grown, so has the demand for potable water. As a result, it is critical to identify water resources from which we can obtain potable water. There are numerous sources of water that do not contain it in a drinkable form. The water is either too high in calcium, magnesium, or any other organic impurity, or it just has foreign particles that make it unfit for drinking.
Water Purification
Boiling
filtration
bleaching powder treatment
SODIS (Solar Water Disinfection) is just a few example.
The most common method for purifying water currently in use is probably boiling. In typical households, it is an effective method; It is not suitable for use in large-scale industrial settings. The reason for this is that the amount of water that needs to be purified in typical homes is very small, making the amount of water lost through evaporation almost nonexistent. However, industrial or large-scale water purification will result in a much lower amount of purified water and a much higher water loss from evaporation.
Water contaminants can also be removed through filtration. This method of purification lacks the ability to remove foreign chemicals and impurities that are soluble in water, which is a major drawback.
The United Nations recommends SODIS, or Solar Water Disinfection, for disinfecting water with soft drink bottles, sunlight, and a black surface—at least in hot countries with frequently intense sunlight.
The water-filled transparent bottles can be sterilized by exposing them to intense sunlight for approximately five hours in a horizontal position atop a flat surface. If the bottom half of the bottle or the surface it is lying on is blackened, or if the flat surface is made of plastic or metal, the process is even safer and more effective. The organisms are destroyed by the combination of heat and ultraviolet light.
This method of purification cannot be utilized in countries with cold climates, which is its primary drawback. Additionally, the purification process takes longer and requires a "blackened" surface, similar to solar cookers.
Need for a stable method of purification
As a result, we require a method of purification that can be utilized at any time and from any location, does not require the use of any content from a third party, and is also economically viable on both small and large scales.
Therefore, we examine the process of treating water with bleaching powder, also known as "Chlorination," to purify it.
THEORY
The theory of how water was cleaned in different parts of the world in the past.
A cholera epidemic was found to have spread through water in 1854. In locations where sand filters were installed, the outbreak appeared to be less severe. John Snow, a British scientist, discovered that sewage water contamination at water pumps was the primary cause of the outbreak. He disinfected the water by adding chlorine to it to make it clean. The conclusion that good taste and smell alone do not guarantee safe drinking water was reached after the pump's water had normal tastes and smells. Because of this discovery, governments began installing chlorination and sand filters in their municipal water supplies, which resulted in the first government regulation of public water.
In order to safeguard the health of the general public, the United States of America began manufacturing substantial sand filters in the 1890s. These proved to be successful. Rapid sand filtration was now used in place of slow sand filtration. The capacity of the filter was increased by cleaning it with strong jet steam. Dr. Fuller then discovered that coagulation and sedimentation techniques preceded rapid sand filtration to improve its effectiveness. In the meantime, water-borne diseases like cholera and typhoid decreased as the chlorination of water spread worldwide.
However, chlorination's victory did not last for very long. The undesirable effects of this component were eventually discovered. Since chlorine vaporizes much more quickly than water, it was linked to respiratory disease aggravation and development. Experts in the water started looking for new ways to disinfect water. In Belgium's drinking water supply in 1902, ferric chloride and calcium hypochlorite were combined, causing coagulation and disinfection.
One of the greatest achievements of the twentieth century was the safe distribution and treatment of water. Thousands of people in the United States died annually from cholera, typhoid fever, dysentery, and hepatitis A before chlorine was used to treat drinking water on a regular basis in cities (Chicago and Jersey City in the United States were the first to do so in 1908).
In the United States and other developed nations, chlorination and filtration of drinking water have substantially reduced the prevalence of these diseases. To achieve clean, safe drinking water, a multi-barrier strategy that includes: safeguarding the safe distribution of treated water to consumers' taps, appropriately treating raw water, and protecting source water from contamination. Chlorine is added to drinking water as elemental chlorine (chlorine gas), sodium hypochlorite solution, or dry calcium hypochlorite during the treatment process.
Each of these forms "free chlorine" when applied to water
which kills pathogenic (disease-causing) organisms.
Almost all water disinfection systems employ a method based on chlorine
either alone or in conjunction with other disinfectants.
Chlorination has a number of advantages, including the control of pathogens that cause disease:
Including
Reduces numerous unpleasant tastes and odors;
Eliminates slime bacteria, molds, and algae that commonly grow in storage tanks, water main walls, and water supply reservoirs;
removes chemical compounds that hinder disinfection and have a bad taste; and aids in the removal of manganese and iron from raw water.
Importantly, only chlorine-based chemicals provide "residual disinfectant" levels that help safeguard treated water throughout the distribution system and prevent microbial regrowth.
Bleaching powder has significantly improved the safety of drinking water supplies for more than a century. By disinfecting our drinking water, we ensure that it is free of microorganisms that are capable of causing diseases like cholera and typhoid fever, which can be fatal. Bleaching powder continues to be the disinfectant that is used the most frequently in drinking water and for which we have the most scientific data. As part of the process of treating the water for drinking, bleaching powder is added. However, bleaching powder also reacts with decaying leaves and other organic matter found naturally in water. Disinfection by-products are a group of chemicals produced by this chemical reaction.
The benefits of bleaching our drinking water (less disease) outweigh any health risks from THMs and other byproducts, according to current scientific data. Experts in water treatment continue to use bleaching powder, despite the availability of other disinfectants. Chlorine is effective against virtually all microorganisms when used in conjunction with current water filtration techniques. This level of effectiveness ensures that microorganisms cannot recontaminate the water after it leaves the treatment facility because bleaching powder is simple to apply and small amounts of the chemical remain in the water as it travels through the distribution system from the treatment plant to the consumer's tap.
What exactly is bleaching powder and how is it made?
Calcium hypochlorite, also known as bleach, is a chemical compound with the formula Ca(ClO) 2. It is frequently used as a bleaching agent and for treating water. In comparison to sodium hypochlorite (liquid bleach), this chemical is thought to be relatively stable and has more chlorine available.
It is prepared by either the calcium process or the sodium process. Calcium Process
2 Ca(OH)2 + 2 Cl2 Ca(ClO)2 + CaCl2 + 2 H2O Sodium Process
2 Ca(OH)2 + 3 Cl2 + 2 NaOH Ca(ClO)2 + CaCl2 + 2 H2O + 2 NaCl
But how can this chemical be used to sterilize water?
This chemical can be used for sterilizing water by Using 5 drops of bleach per each half gallon of water to be purified and allowing it to sit undisturbed for half an hour to make it safe for drinking. Letting it sit for several hours more will help reduce the chlorine taste, as the chlorine will slowly evaporate out. A different reference advises when using household bleach for purification; add a single drop of bleach per quart of water that is visibly clear or three drops per quart of water where the water is NOT visibly clear. Then allow the water to sit undisturbed for half an hour.
What are the actual processes involved in disinfecting and purifying water?
The combination of the following processes is used for municipal drinking water treatment worldwide:
Pre-chlorination – for algae control and arresting any biological growth
Aeration – along with pre-chlorination for removal of dissolved iron and manganese
Coagulation – for flocculation
Coagulant aids also known as polyelectrolytes – to improve coagulation and for thicker floc formation
Sedimentation – for solids separation, that is, removal of suspended solids trapped in the floc
Filtration – for removal of carried-over floc
Disinfection – for killing bacteria
Out of these processes, the role of Bleaching powder is only in the last step i.e. for the Disinfection of water.
EXPERIMENT
Aim:
To Determine the dosage of bleaching powder required for sterilization or disinfection of different samples of water.
Requirements:
Burette, titration flask, 100ml graduated cylinder, 250ml measuring flask, weight box, glazed tile, glass wool.
Bleaching Powder, Glass wool, 0.1 N Na2S2O3 solution, 10% KI solution, different samples of water, and starch solution.
Pre-Requisite Knowledge:
1. A known mass of the given sample of bleaching powder is dissolved in water to
prepare a solution of known concentration. This solution contains dissolved chlorine,
liberated by the action of bleaching powder with water.
CaOCl2+H20 I >> Ca(OH)2+Cl2
2. The amount of Chlorine present in the above solution is determined by treating a
a known volume of the above solution with an excess of 10% potassium iodide solution,
when an equivalent amount of Iodine is liberated. The Iodine, thus liberated is then
estimated by titrating it against a standard solution of Sodium thiosulphate, using
the starch solution as an indicator.
Cl2+2KI i > 2KCl+I2 I2+2Na2S2O3 i > Na2S4O6+2NaI
A known Volume of one of the given samples of water is treated with a known volume of bleaching powder solution. The amount of residual chlorine is determined by adding excess potassium iodide solution and then titrating it against standard sodium thiosulphate solution.
From the readings in 2 and 3, the amount of chlorine and hence bleaching powder required for the disinfection of a given volume of the given sample of water can be calculated.
Procedure:
Preparation of bleaching powder solution. Weigh accurately 2.5g of the given sample of bleaching powder and transfer it to a 250ml conical flask. Add about 100-150ml of distilled water. Stopper the flask and shake it vigorously. The suspension thus obtained is filtered through glass wool and the filtrate is diluted with water (in a measuring flask) to make the volume 250ml. The solution obtained is a 1% bleaching powder solution.
Take 20ml of the bleaching powder solution in a stoppered conical flask and add it to 20ml of the 10% KI solution. Stopper the flask and shake it vigorously. Titrate this solution against 0.1N Na2S2O3 solution taken in the burette. When the solution in the conical flask becomes light yellow in color, add about 2ml of starch solution. The solution now becomes blue in color. Continue titrating till the blue color just disappears. Repeat the titration to get a set of three concordant readings.
Take 100ml of the water sample in a 250ml stoppered conical flask and add it to 10ml of bleaching powder solution. Then add 20ml of KI solution and stopper the flask. Shake vigorously and titrate against 0.1N Na2S2O3 solution using starch solution as an indicator as described in step 2.
By Chanchal Sailani | January 21, 2023, | Editor at Gurugrah_Blogs.
