Chlorine is one of the most practical and widely used disinfectants for wastewater. Chlorination is commonly used because it can kill disease-causing bacteria and control nuisance organisms such as iron-reducing bacteria, slime, and sulfate-reducing bacteria. Chlorine destroys target organisms by oxidizing the cellular material of bacteria.
How does chlorination work in wastewater treatment?
Nearly every wastewater treatment facility uses chlorination to disinfect wastewater before the water is sent back out into the environment. The primary goal of chlorination is to disinfect the wastewater and remove any harmful pathogens that are present in the water.
How does chlorination kill bacteria in water?
Chlorination involves adding a measured amount of chlorine to water to produce a residual sufficient to kill bacteria, viruses, and cysts. The killing effect of chlorine depends on the pH of the water, temperature, chlorine level and contact time (i.e., the time the chlorine is in the water before consumption).
When should I add chlorine to my water treatment system?
Chlorination can be done at any time/point throughout the water treatment process - there is not one specific time when chlorine must be added.
Why do we chlorinate our water?
Today, chlorination is the most popular method of disinfection and is used for water treatment all over the world. Why do we Chlorinate our water? A large amount of research and many studies have been conducted to ensure success in new treatment plants using chlorine as a disinfectant.
Why is wastewater treated with chlorine?
Chlorine is the most widely used disinfectant for municipal wastewater because it destroys target organisms by oxidizing cellular material. Chlorine can be supplied in many forms, which include chlorine gas, hypochlorite solutions, and other chlorine compounds in solid or liquid form.
Why is chlorine such as important part of the treatment?
Chlorine's use has seen it help to virtually eliminate waterborne diseases, such as cholera, typhoid and dysentery in developed countries. It also eliminates slime bacteria, molds and algae that commonly grow in water supply areas, on the walls of water mains and in storage tanks.
Why chlorination is most preferred method for disinfection?
Chlorine kills pathogens such as bacteria and viruses by breaking the chemical bonds in their molecules. Disinfectants that are used for this purpose consist of chlorine compounds which can exchange atoms with other compounds, such as enzymes in bacteria and other cells.
Why do we use chlorination?
This method is used to kill bacteria, viruses and other microbes in water. In particular, chlorination is used to prevent the spread of waterborne diseases such as cholera, dysentery, and typhoid.
Is chlorination the best solution for disinfection for our water systems?
Disinfection, a chemical process whose objective is to control disease-causing microorganisms by killing or inactivating them, is unquestionably the most important step in drinking water treatment. By far, the most common method of disinfection in North America is chlorination.
Why is chlorination of waste water not desirable?
Wastewater Disinfection While a chlorine residual is desirable in drinking water treatment, it is not desirable in wastewater treatment where chlorine discharged to the natural environment may adversely impact wildlife. Chlorine is able to achieve disinfection goals through bacteria and virus inactivation.
Why is chlorine added to wastewater 7?
Sedimentation tank Impurities are settle in the bottom of tank. Sand and gravel and sand filter Remove the dirt from the water. Chlorinating tank Chlorine is mixed in water to disinfect the eater and to kill the germs.
What is the effect of chlorine in water?
Drinking water chlorination is the addition of chlorine to drinking water systems. It is the most common type of drinking water disinfection. Disinfection kills bacteria, viruses, and other microorganisms that cause disease and immediate illness.
What is chlorination very short answer?
Chlorination is the process of adding chlorine to drinking water to disinfect it and kill germs. Different processes can be used to achieve safe levels of chlorine in drinking water. Chlorine is available as compressed elemental gas, sodium hypochlorite solution (NaOCl) or solid calcium hypochlorite (Ca(OCl)2.
Chlorination
The STP treats the wastewater coming from agriculture, sewage and industrial plants. The treatment process has four stages (pretreatment, primary, secondary and tertiary treatment).
Chlorine Compounds as Disinfectant
We can add chlorine into the tertiary system via chemical feed inlets. Three standard formulations of chlorine are available for chlorination:
Why is chlorination needed in wastewater?
Chlorine needs to be put into wastewater to treat it and oxidize any contaminants it once held when in the sewage system. The chlorination wastewater treatment procedure creates byproducts in treated water.
Why is wastewater chlorination important?
The process of wastewater chlorination achieves one important goal: it disinfects the water and frees it of the harmful pathogens. This must be done, and it happens before the water runs off naturally into oceans, rivers and streams.
Why is chlorination important in water treatment?
In order to combat waterborne diseases, different disinfection methods are used to inactivate pathogens. Along with other water treatment processes such as coagulation, sedimentation, and filtration, chlorination creates water that is safe for public consumption.
What is the purpose of adding chlorine to water?
The main objective of this chlorine addition is to disinfect the water and maintain chlorine residuals that will remain in the water as it travels through the distribution system.
What is the combination of free chorine and hypochlorite?
At lower pH levels, the hypochlorous acid will dominate. The combination of hypochlorous acid and hypochlorite ions makes up what is called ‘free chorine.’. Free chlorine has a high oxidation potential and is a more effective disinfectant than other forms of chlorine, such as chloramines.
What is chlorine breakpoint?
Residual Chlorine, Breakpoint. Any type of chlorine that is added to water during the treatment process will result in the formation of hypochlorous acid (HOCl) and hypochlorite ions (OCl-), which are the main disinfecting compounds in chlorinated water. More detail is provided later on in this fact sheet.
How is calcium hypochlorite made?
Calcium hypochlorite (CaOCl) is made up of the calcium salts of hypochlorous acid. It is produced by dissolving chlorine gas (Cl 2) into a solution of calcium oxide (CaO) and sodium hydroxide (NaOH). Calcium hypochlorite is a white, corrosive solid that comes either in tablet form or as a granular powder. Calcium hypochlorite is very stable, and when packaged properly, large amounts can be purchased and stored until needed. The chemical is very corrosive however, and thus requires proper handling when being used to treat water. Calcium hypochlorite needs to be stored in a dry area and kept away from organic materials. It cannot be stored near wood, cloth or petrol because the combination of calcium hypochlorite and organic material can create enough heat for an explosion. It must also be kept away from moisture because the tablets/granular powder readily adsorb moisture and will form (toxic) chlorine gas as a result. Calcium hypochlorite has a very strong chlorine odour – something that should be kept in mind when placing them in storage.
What happens after chlorine demand is met?
After the breakpoint, any additional chlorine added will result in a free chlorine residual proportional to the amount of chlorine added.
How much calcium hypochlorite is needed for water treatment?
Compared to the 1-16 mg/L required with chlorine gas, only 0.5-5 mg/L of calcium hypochlorite is required. When calcium hypochlorite is added to water, hypochlorite and calcium ions are produced.
What is the process of adding chlorine to water?
Chlorination. Chlorination involves adding a measured amount of chlorine to water to produce a residual sufficient to kill bacteria, viruses, and cysts.
What is the final step in chlorine treatment?
Typically, chlorine is added to public drinking water as the final stage of treatment, often following an upstream filtration step which removes sediment that can tie up chlorine and shield organisms from its effect .
What are the reactions between free chlorine and these acids?
Reactions between free chlorine and these acids may produce a class of compounds called trihalomethanes. Strategies to reduce these in public water supplies include enhanced filtration for better organic removal and use of ammonia together with chlorine to produce chloramines for use in lieu of chlorine.
What is the chemical that is added to water to make trihalomethanes?
Chloramines have longer half-life in the water and are less likely to produce trihalomethanes. Chlorine is typically added to water using chemical feed systems to inject liquid sodium hypochlorite (bleach) solution or added as gaseous chlorine (typical of larger public water treatment plants).
Can chlorine be used in water?
Chlorine cannot be used in most high purity water loops without contaminating the process or interfering with the end use of the water. These systems often rely on ultraviolet disinfection as an alternative to water chlorination.
Does chlorine react with organic compounds?
Unfortunately, chlorine reacts with many organic compounds to form chlorine disinfection by-products that are recognized as potent carcinogens at low levels of concentrations. Such organic compounds include humic and fulvic acids, which derive from rotting vegetation common in surface waters.
What is chlorine used for?
Chlorine is a powerful oxidizer that is commonly used in wastewater treatment for disinfection and odor control, bulking control, and other applications. When chlorine is added to a unit process, we want to ensure that a measured amount is added. Chlorine dose depends on two considerations - the chlorine demand and the desired chlorine residual.
How is chlorine dose determined?
It may be determined by adding excess chlorine to water and then by measuring the difference between the added amount of chlorine and the residual chlorine after a specified time period. The chlorine requirement, or chlorine dosage, is the sum of the chlorine demand and the desired chlorine residual.
What is the solubility of water?
A water solution is a homogenous liquid consisting of the solvent (the substance that dissolves another substance) and the solute (the substance that dissolves in the solvent). Water is the solvent. The solute, whatever it may be, may dissolve up to a certain point. This is called its solubility - that is, the solubility of the solute in the particular solvent (water) at a particular temperature and pressure. Remember, in chemical solutions, the substance being dissolved is the solute, and the liquid present in the greatest amount in a solution (and that does the dissolving) is the solvent. We should also be familiar with another term - concentration, which is the amount of solute dissolved in a given amount of solvent. Concentration is measured as:
What are the diseases that are associated with wastewater?
Wastewater contains many types of human enteric organisms that are associated with various waterborne diseases. Typhoid, cholera, paratyphoid, and bacillary dysentery are caused by bacteria, and amebic dysentery is caused by protozoa. Common viral diseases include poliomyelitis and infectious hepatitis. Disinfection refers to selective destruction of disease-causing organisms in the wastewater effluent. The term sterilization denotes the complete destruction of all organisms. Pasteurization is selective destruction of undesired organisms by heat.
Is chlorine a gas?
Chlorine is yellow-green in the gas form and amber colored in liquid form. It is 2.5 times heavier than air, non-flammable and a very strong oxidizing agent. The pressurized containers normally contain approximately 80% liquid chlorine and 20% gas. Although chlorine can be fed directly into the wastewater, most facilities dissolve the chlorine gas in water to reduce safety risks and facilitate movement to the point of application.
Is hypochlorite a substitute for chlorine?
Hypochlorite is less hazardous than chlorine; therefore, it is often used as a substitute chemical for elemental chlorine. Hypochlorite is similar to strong bleach and comes in two forms: dry calcium hypochlorite, often referred to as HTH, and liquid sodium hypochlorite. Calcium hypochlorite contains about 65% available chlorine; sodium hypochlorite contains about 12 to 15% available chlorine, in industrial strengths.