The acceptable water hardness range is between 60120 mgl as caco 3. Lime is used to remove chemicals that cause carbonate hardness. The deep bed filter is implemented in the oil removal step orf, prior to the lime softening process, and the softening step after filter, post lime softening. The precipitated caco 3 and mgoh 2 are filtered off. Sep 27, 2016 ionexchange resins method remove hardness of water demineralised or deionised water duration. Magnesium carbonate mgco 3, unlike calcium carbonate, does not precipitate in cold water. Softeners may also remove as much as 510 ppm parts per. A lime dosage range of 30180% of the stoichiometric amount. Soda lime is a process used in water treatment to remove hardness from water. Lime soda process is one of the water softener systems. Water softening is usually achieved using lime softening. Addition of lime cao and soda na 2 co 3 to the hard water precipitates calcium as the carbonate, and magnesium as its hydroxide.
The three most common precipitative softening alternatives include lime softening, limesoda ash softening, and caustic softening. Despite all the benefits of lime softening there are also some adverse effects. Depending on the type of water softening process used, softening may also aid in other water treatment processes. This process is now obsolete but was very useful for the treatment of. When lime and soda ash are added to water, hardness causing minerals such as calcium and magnesium are precipitated out. Limesoda water softening process and its advantages notes.
A water softening experiment was conducted in replicate to observe the changes in parameters such as total hardness, calcium hardness, magnesium hardness, alkalinity and ph with varying dosages of lime. Water softening is an important process, because it can extend the lifespan of household appliances and pipelines, as well as improve function and lifespan of solar heating systems, air conditioning units and many other water based applications. Lime cannot remove the calcium permanent hardness which. Lime softening is typically used for water containing low concentrations of noncarbonate hardness. The chemistry of limesoda ash precipitation water softening. Hardness is the term often used to characterize a water that. Water treatment plant operation chapter 14 softening. Well water in the northern parts in sri lanka is encountering with the problem of water hardness. The precipitation reactions with lime and soda are very slow. Water resources engineering civil engineering engc 6305. Addition of lime cao and soda na2co3 to the hard water precipitates calcium as the carbonate, and magnesium as its hydroxide. However, added magnesium oxide and good sludge contact will improve results. For municipal water supply softening is used to reduce the total hardness in the raw water to. Same way cooling water should be free from temporary water hardness.
Lime soda a batch process b continuous process cold limesoda hot limesoda 2. A cost effective technique for chemical wastes reduction. As a result precipitation becomes almost complete very quickly. Limesoda ash softening process 10 when lime and soda ash are added, hardnesscausing minerals form nearly insoluble precipitates. The unique features of our lime softeners allow this equipment to treat the hot produced water in the sagd process. Limesoda softening reactions by adding hydrated lime, the following reactions results in the precipitation of solid calcium carbonate and magnesium hydroxide 4.
Introduction lime soda process is a method of softening hard water. Hot process softeners increase the rate of chemical reactions and give better quality water. Ion exchange is accomplished by passing the water through columns of a natural or synthetic resin that trades sodium ions for calcium and magnesium ions. Oct 09, 2018 water softening is a process through which calcium, magnesium and certain other metal cations in hard water are removed. This article first covers how gravity clarifiers work, some of the chemicals used in clarification, proper chemical feeding procedures, and clarifier equipment designs. The water chemist distinguishes between cold process lime softening, usually carried out in the range of 40 to 9o0f 4 to 320c, and hot process, at 215 to 23o0f 102 to 11o0c. Chemical precipitation is one of the more common methods used to soften water. Lime soda ash softening process 10 when lime and soda ash are added, hardnesscausing minerals form nearly insoluble precipitates. A water softening process in which water is treated with hydrated lime sometimes in combination with soda ash, which reacts with dissolved calcium and magnesium compounds to form precipitates that can be removed as sludge. What is the hot lime soda process of water treatment.
In five of these plants, little or no calcium car bonate was present. This helps prepare water for direct use as cooling tower makeup or as a firststage treatment followed by ion exchange for boiler makeup or ro reject recycle. The selection of one of these alternatives is based on cost, water quality and owner and operator preferences. It also explains how cold lime softening works, and provides guidance on maintaining system reliability. Lime soda softening may also be classified as hot or cold, depending on the temperature of the water. At the site, the oil removal filter influent is between 100 ppm and 300 ppm with an effluent less the 3 ppm oil and solids. In this system calcium hydroxide and soda ash are used as reagents.
The resulting soft water requires less soap for the same cleaning effort, as soap is not wasted bonding with calcium ions. Produced specifically for water treatment operator training, this new video from awwa illustrates and explains lime softening processes, chemistry, and feed calculations. Zeolite softeners can be used to remove residual hardness in the effluent from a hot process lime or lime soda softener. Advantages and disadvantages of lime softening biotech. Once water hardness is known, you have two options.
Apr 25, 2017 lime soda process is one of the water softener systems. Chemicals normally used are lime calcium hydroxide, caoh 2 and soda ash sodium carbonate, na 2co 3. The hot lime soda process, by using hot water, is invariably used for boiler feed water. The most common gravityclarification process is cold lime softening. Only calculated amounts of lime and soda are to be added. In this process it is possible to remove magnesium water hardness nearly completely but calcium hardness may be remains more than 40ppm. Awwa shows lime softening techniques for water operators.
This article will discuss lime softening through a new perspective, instead of going through the detailed chemical equations. The high ph associated with lime softening can aid in disinfection. The equipment and operation of a hot zeolite softener is identical to that of an ambient. Would anyone be able to recommend a source for hot lime softener modeling software to help calculate lime, soda ash and mgo feed rates for treatment of a given water. Know the differences among the three lime soda softening process alternatives described be able to recommend the choice of the three lime soda softening process alternatives to use for a water sample with a known value of magnesium hardness and knowledge of whether the water is from a groundwater source or from a surface water source. Lime softening, also known as clarks process, is a type of water treatment used for water softening which uses the addition of limewater calcium hydroxide to remove hardness calcium and magnesium ions by precipitation. Limesoda softening may also be classified as hot or cold, depending on the temperature of the water.
Apr 03, 2017 lime and soda process is used for water softening in this video i explain how it works suggested books for chemistry engineering chemistry b. Lime softening lime softening is an operation which has been used for the past 150 years to remove hardness and soften the water. The process decreases the acidity that is associated with the minerals in the hard water. Ion exchange process for water softening hindi youtube. In small systems, lime softening is typically practiced by adding hydrated lime to raw water to. Lime softening, also known as clark s process, is a type of water treatment used for water softening which uses the addition of limewater calcium hydroxide to remove hardness calcium and magnesium ions by precipitation. Cold limesoda process article about cold limesoda process. The limesoda method of water softening must be followed by sedimentation and filtration in order to remove the precipitates. Determination of the bicarbonate concentration in moles per liter alkalinity is assumed to be in the bicarbonate form since the ph is 7. Water treatments softener water treatment waste water. The process is also effective at removing a variety of microorganisms and dissolved organic matter by flocculation. The aim of the limesoda process is to convert calcium and magnesium compounds to the virtually insoluble forms, calcium carbonate caco 3 and magnesium hydroxide mgoh 2. Pdf process optimization for lime soda water softening. Process for softening of water by zeolite process,hard water is percolated at a specified rate through a bed of zeolite, kept in a cylinder.
Currently i am working on hot lime softening project. Zeolite softeners can be used to remove residual hardness in the effluent from a hot process lime or limesoda softener. Lime softening is a very viable way of water softening because when it is added to the hard water, it dissolves all the minerals in the hard water. Ionexchange resins method remove hardness of water demineralised or deionised water duration. According to the sri lanka standards for potable water sls 614, the highest desirable level of total hardness is 250 ppm. Predicted analyses of a typical raw water treated by various lime and lime soda softening processes are presented in table 61. Effectiveness 80100 mgl as caco3 is usually considered acceptable result of limesoda ash softening, as long as mg is limesoda method chemistry britannica. Jan 22, 2014 hot lime soda process in the hot lime soda process the reactions take place at higher temperature near about boiling point of water.
Effectiveness 80100 mgl as caco3 is usually considered acceptable result of lime soda ash softening, as long as mg is lime and soda ash to remove a meq of x initially present x lime soda ash co2 cahco32 mghco32 mgco3 mgso4 caso4 water softening. For municipal water supply softening is used to reduce the total hardness in the raw water to than 40 mg1 optionally 1 as caco 3. Limesoda water softening process limitation of soda. The chemical mixing process is same as the cold lime soda process, but steam is applied in mixture tank. The effluent from the hot process is reasonably soft and has a hardness of about 2025 ppm only. Modern day processes for water softening usually treat the water in four steps to make is acceptable for human use. For waters with high calcium, high magnesium, and carbonate and noncarbonate hardness. Soda ash is used to remove chemicals that cause noncarbonate. Lime soda water softening method is one of the most traditional chemical methods in water purification process used for reducing the hardness of well water. The use of lime to soften water originated around 1841 when the thames river was treated for its bicarbonate hardness. These must be softened by other methods, including lime soda or, more frequently, ion exchange softening described below. Water supply and pollution control mit opencourseware. In one plant, mag nesium hydroxide, as well as calcium carbonate, was found in a coldwater line deposit table 2.
This process is now obsolete but was very useful for the treatment of large volumes of hard water. Water softening is the removal of calcium, magnesium, and certain other metal cations in hard water. Cold lime softening process is used to reduce raw water hardness, alkalinity, silica, and other constituents. Hot lime soda process in the hot lime soda process the reactions take place at higher temperature near about boiling point of water. The three most common precipitative softening alternatives include lime softening, lime soda ash softening, and caustic softening. Lime softening water treatment lime softening process. Lime soda a batch process b continuous process cold limesoda. Since 1976, ecodyne has supplied hot lime softeners for the removal of hardness, alkalinity, turbidity, oxygen, silica removal and other contaminants in otsgs and boilers. Limesoda ash softening is a well established water treatment process. The hot process effluent flows through filters and then through a bed of strong acid cation resin in the sodium form figure 87. The ion exchange water softening process can remove nearly all calcium and magnesium from source water.
In the lime softening process, the ph of the water being treated is raised sufficiently to precipitate calcium carbonate and, if necessary, magnesium hydroxide. Cold lime softening sewage treatment reverse osmosis. Calculations are presented for daily chemical requirements and solids production rates. Limesoda water softening process limitation of soda lime. Is a process in which carbon dioxide is bubbled into the water being treated to lower the ph. You can live with the hardness level, recognizing that levels below 7. Soft water also extends the lifetime of plumbing by reducing or eliminating scale buildup in pipes and fittings. Advantages and disadvantages of water softening water. There is also information about three lime soda water softening process alternatives two stage excess lime water softening, split treatment, and selective calcium removal, along with calculation of the dosages needed for lime, soda ash, and carbon dioxide. Lime reacts with temporary hardness, co 2, acids, bicarbonates and alums. In the limesoftening process, the ph of the water being treated is raised sufficiently to precipitate calcium carbonate and, if necessary, magnesium hydroxide. Mar 03, 2014 lime soda process softening of water 1.
By this process soluble magnesium and calcium salts are removed as calcium carbonate and magnesium hydroxide precipitated. Cold or warm process softening is not as effective as hot process softening for silica reduction. Conventional water softening is most often based a process known as ion exchange, utilizing a synthetic polymeric plastic material in the form of very small beads called ion exchange resin. Perhaps just an excel spreadsheet program to share and perhaps build upon. The coagulant may be supplemented by an anionic or a nonionic flocculant. Pravendra tomar pt sir iitjee, neet 68,347 views 8.