Water Properties and Treatment PDF

# WATER - Water is one of the basic materials of life on the Earth. - It is of prime importance for the preservation of all human activities - domestic, agricultural, and industrial demand of water. - Only 71% of the Earth is composed of water, but only less than 1% of world's water resources are a...

# WATER - Water is one of the basic materials of life on the Earth. - It is of prime importance for the preservation of all human activities - domestic, agricultural, and industrial demand of water. - Only 71% of the Earth is composed of water, but only less than 1% of world's water resources are available for ready use. - It is known as the universal solvent. - Pure water is composed of parts of hydrogen and dissolved oxygen. - By volume, it is 1 part of oxygen, and 2 parts of hydrogen. - These dissolved salts are the impurities of water. - As engineering material water is used for producing steam in boilers to generate hydroelectric power, furnishing steam for engines, for refrigeration, and A/C. - It is used for construction of concrete structures for manufacturing purposes. # Impurities Of Water | Impurities | Description | |---|---| | **Suspended** | - Not soluble in H₂O. - Particle form (big). - Dispersed in H₂O. | | **Colloidal** | - Colloidal in nature. - Particle size small. - Humic Acid. - Finely divided silica. - Clay, organic matter. | | **Dissolved** | - Dissolved gases (CO₂, O₂, NH₃, SO₂, H₂S, gas) | | **Pathogenic** | - Contain bacteria, fungi, virus, etc.. - Causes diseases such as cholera, dysentery, etc. | **Impurities in Water** - **Suspended** - Not soluble in H₂O - Particle form (big) - Dispersed in H₂O - **Colloidal** - Colloidal in nature - Particle size small - Humic acid - Finely divided silica - Clay, organic matter - Organic (amino acid) - **Dissolved** - Inorganic - Dissolved gases (CO₂, O₂, NH₃, SO₂, H₂S Gas) - Anion - Negative Charge - F^-, Na⁺, Ca⁺², Mg⁺², SO₄^-2, NO₃^- - Cation - Positive charge - Cl^-, Na⁺, Ca⁺², Mg⁺², SO₄^-2, NO₃^- - Makes the H₂O corrosive in nature - Makes the water turbid - Makes the water - Turbid - Coloured - Bad smell - Makes the water hard - **Dissolved Organic Matter** - Urea, thiourea, pesticides # Hardness Of Water - It is a measure of the total concentration of calcium and magnesium ions expressed as calcium carbonate. - The nominal amount of heavy metals like Fe (as Fe⁺²) may be dissolved too. - It is a property which prevents the leathering of soap. - Soaps are sodium or potassium salts of higher fatty acid like oleic acid C₁₇H₃₃COONa and stearic acid C₁₇H₃₅COONa. - Hard water does not give lather with soap. - When soap comes in contact with soft water, leather is produced due to sodium stearate: - C₁₇H₃₅COONa + H₂O -> C₁₇H₃₅COOH + NaOH - (Sodium stearate) -> (Stearic Acid) # Soap With Hard Water ## Reactions: - When soap comes in contact with hard water, sodium stearate will react with dissolved calcium and magnesium salts and produce calcium stearate and magnesium stearate which is an insoluble white ppt. Thus, the insoluble white ppt prevents leathering of soap. - 2C₁₇H₃₅COONa + CaCl₂ -> (C₁₇H₃₅COO)₂Ca + 2NaCl - (Sodium stearate) -> (Insoluble scum / ppt) - 2C₁₇H₃₅COONa + MgSO₄ -> (C₁₇H₃₅COO)₂Mg + Na₂SO₄ - (Sodium stearate) -> (Insoluble scum / ppt) - Different types of water have different degrees of hardness. These are classified on the basic of degree of hardness as follows: | Hardness | Name of Water | |---|---| | 0-70 mg/L | Soft water | | 70-150 mg/L | Moderate hard water | | 150-300 mg/L | Hard water | | 300 mg/L & above | Very hard water | # Degree Of Hardness - The total hardness of water is caused by dissolved calcium and magnesium salts of Ca(HCO₃)₂, MgCl₂, Mg(HCO₃)₂, CaSO₄, MgSO₄, Ca(NO₃)₂, etc. - Hardness of water is expressed in terms of calcium carbonate equivalents. - The weight of different hardness salts causing hardness are converted to weight equivalent to that of calcium carbonate. - CaCO₃ is selected for the expression of hardness because the molecular weight of CaCO₃ is 100, which is easy for calculation & it is the most insoluble salt of all and dissolved salts of calcium are precipitated as CaCO₃. | Name of Salt | Molecular Wt. | |---|---| | Ca(HCO₃)₂ | 162 | | Mg(HCO₃)₂ | 146 | | CaCl₂ | 111 | | CaSO₄ | 95 | | MgSO₄ | 136 | | CaCO₃ | 100 | - The method for calculating degree of hardness will be clear from the following formula: Hardness of water = Amount of hardness using salt x 100 in terms of CaCO₃ / Mol. wt. of hardness causing salt equivalents Here, 100 = molecular wt. of CaCO₃. # Expression Of Hardness ## Units: - **1 ppm (parts per million)** - Parts per million of CaCO₃ equivalent hardness per 10⁶ parts of water. - 1 ppm → 1 part of CaCO₃ equivalent hardness present in 10⁶ parts of water. - **mg per litre** - No of milligrams of calcium carbonate equivalent hardness in 1 litre of water. - 1 mg/L = 1 mg of CaCO₃ equivalent hardness in 1 litre of H₂O. - 1L = 1 kg = 1000 g = 1000 x 1000 mg = 10⁶ mg - 1 mg/L = 1 mg of CaCO₃ eq. per 10⁶ mg of H₂O = 1 ppm. - **Degree Clark (°Cl)** - No. of grains (1/7000 lb) of CaCO₃ equivalent hardness per 70,000 parts of H₂O. - 1 Clark = 1 grain of CaCO₃ equivalent hardness per gallon of H₂O. - 1 part of CaCO₃ of hardness per 70,000 parts of H₂O. - **Degree French (°Fr)** - Parts of CaCO₃ equivalent hardness per 10⁵ parts of water. - 1 °French = 1 part of CaCO₃ per 10⁵ parts of water. - **Milliequivalent per litre** - No. of milliequivalents of hardness tat per litre of H₂O. - 1 meq/L = 1 meq of CaCO₃ per litre of H₂O. So, 1 mg/L of CaCO₃ eq. = 50 ppm. # Relation Between Various Units Of Hardness - 1 ppm = 1 mg/L = 0.1 °Fr = 0.07 °Cl = 0.02 meq/L - Suppose total hardness of water sample = 121 ppm. - 121 ppm = 121 mg/L - 121 x 0.07 = 8.47 °Cl & 121 x 0.1 = 12.1 °Fr - Permanent hardness = 101 mg/L, 101 ppm, 7.07 °Cl, 10.1 °Fr - Temporary hardness = 20 mg/L, 20 ppm, 1.4 °Cl, 2.0 °Fr # Types Of Hardness - There are two types of hardness. - **1) Temporary Hardness** - It is caused mainly due to the presence of dissolved bicarbonates of calcium and other heavy metals. - The salts mainly responsible for temporary hardness are Ca(HCO₃)₂ and Mg(HCO₃)₂. - When bicarbonates are decomposed, yielding insoluble carbonates (by boiling), that can be removed by filtration. - **2) Permanent Hardness** - It is due to the presence of dissolved chlorides and sulphates of Ca, Mg, Fe & other metals. - The salts are responsible for permanent hardness are CaCl₂, MgCl₂, CaSO₄, MgSO₄, FeSO₄, Al₂(SO₄)₃. - Permanent hardness can’t be removed by boiling but it can be removed by the use of chemical agents. - Total hardness of water = T.H + P.H - T.H = Temporary Hardness - P.H = Permanent Hardness # Determination Of Hardness By Clark's Test - This method of test in for removal of temporary hardness. - This impurities of Ca(HCO₃)₂, Mg(HCO₃)₂ present. - Slaked lime (Ca(OH)₂) is added with hard water, then insoluble CaCO₃ is formed which is removed by filtration. - Ca(HCO₃)₂ + Ca(OH)₂ -> 2CaCO₃ + 2H₂O - Mg(HCO₃)₂ + Ca(OH)₂ -> CaCO₃ + MgCO₃ + 2H₂O # Estimation Of Hardness Of Water By EDTA Method (Complexometric Titration) - Hardness in water is due to the presence of dissolved salts of Ca & Mg. It is unfit for drinking and bathing. It also forms scales in boilers. - Hence, it is necessary to estimate the amount of the hardness producing substance that is in the water sample. - The estimation of hardness is based on complexometric titration. - Hardness of H₂O is determined by titrating with a standard solution of ethylene diamine tetra acetic acid (EDTA), which is a complexing agent. - EDTA is a reagent that forms EDTA-metal complexes with many metal ions. - In alkaline condition (PH ≥ 9), it forms stable complexes with the alkaline earth metal ions Ca⁺² & Mg⁺². - EDTA is insoluble in water. Its disodium salt is used as a complexing agent. # Basic Principle: - Total hardness is due to the presence of bicarbonates, chlorides and sulphates of Ca & Mg ions. - The total hardness of water in sample is estimated by titrating the water against EDTA using Eriochrome Black-T (EBT) indicator. - Initially EBT forms a weak EBT-Ca⁺² or Mg⁺² wine red coloured complex with Ca⁺² / Mg⁺² ions that is in hard water. - On addition of EDTA solution, Ca⁺²/Mg⁺² ions will preferably make a stable EDTA - Ca/Mg complex with EDTA leaving the free EBT indicator in solution which is steel blue in colour in the end. - Thus, the buffer point is the change of colour from wine red to blue. | Ca⁺² / Mg⁺² | EBT (Blue) Buffer sol (PH 9-10) | Ca-EBT / Mg-EBT Wine-red Colour | EDTA | Ca-EDTA / Mg-EDTA (Blue) Colourless stable complex | |---|---|---|---|---| | Hard water | | | | | | | Unstable complex | | | | - So, EDTA methods, the known water sample is titrated against standard EDTA solution using EBT as indicator in solⁿ (PH = 10) in presence of basic buffer solⁿ. - At the end point, the wine red colour changes to blue. - Chemical formula of EBT - C₂₀H₁₂N₃O₇Na₂SO₃ # NUMERICALS - **Q.1) How many grams of FeSO₄ dissolved per litre give 210.5 ppm of hardness? (Fe = 56, S = 32, O = 16, Ca = 40, C = 12)?** - - FeSO₄ = CaCO₃ - 56 + 16 + 32 + (16 * 3) = 100 g - 100 ppm of hardness = 152 g (ppm) of FeSO₄ - 210.5 ppm of hardness = 152 * 210.5 / 100 - = 319.96 ppm of FeSO₄ - = 319.96 mg/L - = 0.31996 g/L of FeSO₄ - Hence, 0.31996 g of FeSO₄ dissolved per litre gives 210.5 ppm of hardness. - **Q.2) Calculate the temporary hardness & permanent hardness, of a sample of water containing Mg(HCO₃)₂ = 7.3 mg/L, Ca(HCO₃)₂ = 16.2 mg/L, MgCl₂ = 9.5 mg/L, CaSO₄ = 13.6 mg/L (Atomic mass of Mg & Ca are 24 & 40 respectively).** - **Sol:** - Mg(HCO₃)₂ = 7.3 * 100 / 146 = 5 mg/L - Ca(HCO₃)₂ = 16.2 * 100 / 162 = 10 mg/L - MgCl₂ = 9.5 * 100 / 95 = 10 mg/L - CaSO₄ = 13.6 * 100 /136 = 10 mg/L - Temporary hardness due to Mg(HCO₃)₂ & Ca(HCO₃)₂ = (5 +10) mg/L = 15 ppm - Permanent hardness due to MgCl₂ & CaSO₄ = (10 + 10) mg/L = 20 ppm # Municipal Water Supply - **Requisite (Requirements) for potable water:** - It should be sparking clear and odourless. - It should be pleasant in taste. - It should be perfectly cool. - Turbidity should not exceed 10 ppm. - It should be free from objectionable dissolved gases like hydrogen sulphide. - It should be free from objectionable minerals such as Pb, arsenic, Cu, & Mg salts. - Alkalinity should not be high. - pH should be about 8.0. - It should be reasonably soft. - Total dissolved solids should be less than 500 ppm. - It should be free from disease-producing micro-organisms. # Steps Involved In Purification Of Water - Natural water from rivers, canals, etc. does not confirm to all the required specifications of drinking H₂O. - For removing various types of impurities the following treatment processes are employed: - **1) Sedimentation** - It is a process of allowing water to stand undisturbed in big tanks, about 5 m deep, when most of the suspended particles settle down at the bottom due to force of gravity. - The clear supernatant water is then drawn from tank with the help of pumps. - The relation period in a sedimentation tank ranges from 2-6 hours. - **2) Coagulation** - The process of removing colloidal impurities by the addition of required amount of certain chemical (called coagulants). - Coagulant, when added to water which an insoluble, gelatinous substance and entangles very fine suspended impurities forming bigger floct flock, which settle down easily. - Coagulants like alum or ferrous sulphate neutralize charge on colloidal particles like Al⁺³ or Fe⁺³ ions with OH^- ions. - After losing their charge, the tiny clay particles come nearer to one another and combine to form bigger particles which settle down fully properly. - For proper mining of coagulants, with water, mixers are employed. - **Chemical Coagulants:** - **1) Alum (K₂SO₄. Al₂(SO₄)₃. 24 H₂O)** - Al₂(SO₄)₃ + Ca(HCO₃)₂ -> 2Al(OH)₃↓ + 3CaSO₄ + 6CO₂ - (Coagulant) (Impurity) (Flocculant) + 6CO₂ - **2) Sodium aluminate (NaAlO₂)** - NaAlO₂ + 2H₂O -> Al(OH)₃↓ + NaOH - (Gelatinous floc of aluminium hydroxide) - The aluminium hydroxide floc causes sedimentation. The NaOH thus produced, ppt the Mg(OH)₂ salt - - MgSO₄ + 2NaOH - > Mg(OH)₂ + Na₂SO₄ - **iii) Ferrous Sulphate (FeSO₄. 7H₂O)** - It gives good result above pH value of 8.5. - It reacts in the presence of alkalinity. - If alkalinity is not that sufficient, lime is also added. - FeSO₄ + Mg(HCO₃)₂ -> Fe(OH)₂↓ + MgCO₃ + CO₂ + H₂O - 4Fe(OH)₃↓ + O₂ + H₂O -> 4Fe(OH)₃↓ - (Heavy floc) - **3) Filtration** - It is the process of removing colloidal matter & most of the bacterias, micro-organisms by passing H₂O through a bed of fine sand & other proper shred granular material. - It is carried out by using sand filter. - **Sand filter consists of a thick top layer of fine sand placed over coarse sand layer and granules of sand are provided with an inlet for water and underdrain channel for filtered water entering the sand. Sediment is uniformly distributed over coarse fine sand and sand pores get clogging due to bad retention of impurities in pores. When rate of filtration become slow, about 2-3 cm of top fine sand layer is scrapped off & replaced with clean sand & filter is put back into sand again. The scrapped sand is washed with H₂O, dried & stored for future use at time of next scrapping operation.** - **4) Sterilization** - It is a process that kills, eliminates all forms of microorganisms in the water. - The process of killing disease-producing bacteria, microbes, organism from water is called disinfection. - The chemicals which are added to H₂O for killing bacteria are called disinfectants. - **(i) By boiling:** - By boiling for 10-15 min., all the disease-producing bacteria are killed. - **(ii) By adding bleaching powder:** - About 1 kg of bleaching powder per 1000 kilolitres of H₂O is mixed. H₂O allowed to stand undisturbed for several hours. The chemical action produces hypochlorous acid (powerful germicide). - Ca(OCl)₂ + H₂O -> Ca(OH)₂ + Cl₂ - Cl₂ + H₂O -> HCl + HOCl (Hypochlorous acid) - Germs + HOCl -> Germs are killed. - **(iii) By Chlorination.** - Cl (either gas or in concⁿ form) produces hypochlorous acid. - Cl₂ + H₂O -> HOCl + HCl (Hypochlorous acid) - Bacteria + HOCl -> Bacteria are killed. - **(iv) Disinfection by Ozone.** - Ozone (O₃) is excellent disinfectant, which is produced by passing cold & dry oxygen through silent electric discharge. - 3O₂ Silent electric discharge -> 2O₃ (Ozone) - Ozone is highly unstable & breaks down, liberating nascent oxygen. - O₃ -> O₂ + [O] (Nascent oxygen) - The nascent oxygen is very powerful oxidizing agent. It kills the bacteria, as well as, oxidises the organic matter in H₂O & thus Ozone is injected into the H₂O & the sterilizing tank is removed from the disinfected water. - The contact period about 10-15 min. - The usual dose strength = 2-3 ppm - **5) Break-point Chlorination (or free-residual Chlorination)** - It involves addition of sufficient amount of chlorine to water. - (a) Organic matter - Oxidation to dioxide. - (b) Reducing substances - Free ammonia is free in raw water, leaving behind mainly ammonia, which possesses disinfectant action against disease-producing bacteria. - The added Cl at the dip or break point is called Break Point Chlorination. - This indicates the point at which free residual Cl begins to appear. - The residual odours disappear. - Break-point chlorination in appearance of H₂O tastes free from bad tastes & odour. - **Advantages:** - It oxidises completely organic compounds, NH₃ & other reducing compounds. - It removes colour in H₂O due to organic matter. - It destroys 100% all disease-producing bacterias. - It removes both odour & taste from the H₂O. - It prevents growth of any weeds in H₂O. - **Disadvantages:** - The equipment is costly & more expensive chemicals are needed. - Output of H₂O contain turbidity. - The process is reduced. Turbidity must be below 10 ppm of it is not by coagulation & filtration. # Softening Methods - **1) Lime - Soda Process** - Cold lime soda - Hot lime soda - ** 2) Zeolite or Permutit Process** - Ion exchange/de-ionization/de-mineralisation process - **3) Lime - Soda Process** - Water used for industrial purpose (such as steam generation) should be sufficient pure. It should be free from hardness-producing salt before put to use. - The process of removing hardness-producing salts from water is known as softening of water. - In Lime-soda process. - The soluble Ca⁺² and Mg⁺² salts in H₂O are chemically converted into insoluble compounds by adding calculated amount of lime (Ca(OH)₂) & soda (Na₂CO₃). - CaCO₃ and Mg(OH)₂ are precipitated, filtered off. - It is a slow process. - For accelerating process, hot lime soda process is used. - Substance that bring down fine particles of ppt called accelerators like activated charcoal are added. - 100 parts by mass of CaCO₃ are equivalent to: - 74 parts of Ca(OH)₂ - 106 parts of Na₂CO₃ - **Lime requirement for softening** - **74/100 [Temp. {Ca⁺² + 2x Temp. (Mg⁺²) + Perm. (Mg⁺²+ Fe⁺² + Al⁺³)} + CO₂ + NT (HCL or H₂SO₄) + HCO₃ - NaAlO₂ ] all in terms of CaCO₃ eq.** - **Soda requirement for softening** - **106/100 [Perm. (Ca⁺² + Mg⁺² + Al⁺³ + Fe⁺²) + H⁺ (HCl or H₂SO₄) + MgSO₄ + HCO₃ - all in terms of CaCO₃ eq.** - **(i) Cold Line - Soda Process:** - Calculated amount of chemicals (lime & soda) are mixed with H₂O at room temp. - The ppt formed are finely divided, so they do not settle down easily & can't be filtered easily. - It is essential to add small amount of coagulants (like alum. aluminium sulphate, sod. aluminate) which forms ppt (flocs), gelatinous ppt of Al(OH)₃ & entraps the fine ppt. - It provides H₂O containing a residual hardness of 50-60 ppm. - NaAlO₂ + H₂O -> NaOH + Al(OH)₃↓ - (sod. aluminate) - Al₂(SO₄)₃ + 3Ca(HCO₃)2 -> 2Al(OH)₃↓ + 3CaCO₃ + 6CO₂ - (Coagulant) (Hardness in H₂O) - **Method:** - Raw water & calculated quantity of chemicals (lime + soda + coagulant) are fed from top into a vertical circular chamber, fitted inside vertical rotating shaft carrying a number of paddles. - As the raw water & chemicals flow down, there is a vigorous mixing & stirring whereby softening of H₂O takes place. - The softened H₂O comes into outer chamber, it rises upward. - The heavy sludge (ppt) settle down in outer chamber by time softened H₂O reaches up. - The softened H₂O then passes through a filtering media (made up of wood fibre) to ensure complete removal of sludge. - Filtered soft H₂O finally flow our through outlet at the top. - Sludge settling at the top bottom of outer chamber is drawn off. - **(ii) Hot Lime - Soda Process:** - It involves treating H₂O softening chemicals at temp. of 80 - 150^oC. - Hot process is operated at a temp. close to the B.P of solⁿ, so process proceed faster. - Softening capacity is high. - ppt / sludge settle down easily, thence no coagulants are added. - Any dissolved gases (such as CO₂ & air) driven out. - Viscosity of softened H₂O is low, so filtration of H₂O become much easier. It has filtering capacity of filters. - It produces H₂O with low residual hardness of 15-30 ppm. - It consists of 3 parts: - Chemicals, steam in mixed raw H₂O, a 'relaxation tank'. - A 'conical sedimentation vessel' in which sludge settle down. - A 'sand filter' which ensures complete removal of sludge from softened H₂O. - **Advantages of Lime - Soda Process** - It is very economical. - The process combined with coagulation, in lesser amount of coagulant shall be needed. - The process, pH value of treated H₂O so corrosion of pipe is reduced. - Besides the removal of hardness, quantity of minerals in H₂O are reduced. - To certain extent Fe, Mn also removed. - Due to alkaline nature of H₂O, amount of pathogenic bacteria is also reduced. - **Disadvantages of Lime - Soda Process:** - For efficient & economical softening careful operations & skilled supervision is required. - Disposal of large amount of sludge poses a problem. - Sludge may be disposed off in raising beds, by drying off the city. - This can remove hardness only upto 15 ppm, which is not good for boilers. - **2) Zeolite or Permutit Process:** - Chemical formula of Zeolite is Na₂Al₂Si₂O₈. - (Crystalline aluminosilicate) - It is hydrated sodium aluminosilicate capable of exchanging reversibly by ion Na⁺ ion for Ca⁺², Mg⁺² producing salt in H₂O (Na₂Al₂Si₂O₈. H₂O) - It is also known as Permutite. - **Zeolites are of two types:** - **a) Natural zeolite:** are non-porous e.g. - natrolite Na₂O. Al₂O₃. 4SiO₂. 2H₂O - **b) Synthetic zeolite:** are porous & powers gel structure. They are prepared by heating china clay, feldspar & soda ash. e.g. - Beta (BEA), Linde type F (EDI). - **Process:** - Hard H₂O is percolated at a specified rate through a bed of zeolite kept in a cylinder. - The hardness causing ions (Ca⁺², Mg⁺², etc) are retained by zeolite as CaZe & MgZe, while outgoing H₂O contains no salts. - **Rxn takes place are as follows:** - Na₂Ze + Ca(HCO₃)₂ -> CaZe + 2NaHCO₃ - Na₂Ze + Mg(HCO₃)₂ -> MgZe + 2NaHCO₃ - Na₂Ze + CaCl₂ (or CaSO₄) -> CaZe + 2NaCl (or Na₂SO₄) - Na₂Ze + MgCl₂ (or MgSO₄) -> MgZe + 2NaCl (or Na₂SO₄) - (Zeolite) (Hardness) - **Regeneration:** - After some time, zeolite is completely converted into Ca & Mg zeolite & it gets exhausted to soften H₂O, ie it is stopped, exhausted. - At this stage, zeolite is reclaimed by treating the bed with a concⁿ of 10% brine (NaCl 10%). - CaZe (MgZe) + 2NaCl → Na₂Ze + CaCl₂ (or MgCl₂) - (exhausted zeolite) (Brine) (Reclaimed zeolite) (washings) - The washing are led to drain & the regenerated zeolite bed thus obtained is used again for softening purpose. - **Limitations of Zeolite Process:** - If the supply of H₂O is turbid, the suspended matter must be removed by the coagulation, filtration before the H₂O is admitted to Zeolite bed, otherwise the turbidity will clog up the pores of zeolite bed making it inactive. - If H₂O contain large quantities of colored ions such as Fe⁺², Mn⁺² & Ba⁺², they must be removed first, because these ions can't be easily regenerated. - Zeolite can't produce Manganese ion. - If that acids like HCl, HF, HBr, H₂SO₄ are in H₂O, they destroy Zeolite bed. So they must be neutralized with soda before admitting H₂O to Zeolite bed. - **Advantages:** - It removes hardness of 10 ppm completely. - The equipment used is compact & occupying small space. - No impurities are precipitated as there is no danger of sludge formation. - The process automatically adjusts itself for variation in hardness of H₂O. - It is quite clean. - It requires less time for softening. - It requires less skill for maintenance as well as operations. - **Disadvantages:** - Water contain more Na salt than in Lime Soda process. - It only replaces Ca⁺² & Mg⁺² ions but by Na⁺ ions, but leaves all acidic ions like HCO₃ & CO₃^-2 as such in softened H₂O. - High turbidity H₂O can't be treated efficiently by this method. Because impurities ger deposited on zeolite bed creating problem for its working. # Comparison of Permutit process with Lime - Soda process | Permutit Method | Lime - Soda Method | |---|---| | 1) H₂O of 10-15 ppm hardness is obtained. | 1) H₂O of 15-50 ppm hardness is obtained. | | 2) Treated H₂O contain larger amount of Na⁺ salts than in original raw water. | 2) Treated H₂O contain lesser amount of Na⁺ salts. | | 3) Cost of plant & material is higher. | 3) Capital cost is lower. | | 4) Operation expenses are lower. | 4) These are higher. | | 5) It can't be used for treating acidic H₂O, because permutit material undergoes disintegration. | 5) There is no such limitation. | | 6) Plant occupies less space. | 6) Plant occupies more space. | | 7) The raw water to be softened must be free from suspended matter, otherwise pores of permutit material are blocked & bed looses its exchange capacity. | 7) There are no such limitation. | | 8) It can operate under pressure & can be made fully automatic. | 8) It can't operate under pressure. | | 9) It involves no problem of setting, coagulation, filtration & removal of sludge. | 9) It involves difficulty in setting, coagulation. filtration & removal of ppt. | | 10) Treated H₂O contains more dissolved salts. | 10) Contain lesser dissolved salts. | # Ion Exchange / De-Ionisation / De-mineralisation Process - Resin are solid viscous substances that are convertible to polymers. - Ion-exchange resins are insoluble cross-linked long chain organic polymers & a microporous structure e.g. - styrene- divinyl benzene or amine-formaldehyde copolymers with contain amino or quaternary ammonium or quaternary phosphonium or tertiary sulphonium groups as an integral part of their resin matrix. - After treatment with dil. NaOH solⁿ, it become capable to exchange their OH^- ions in H₂O for other anions - CH₂-CH-CH₂-CH-CH₂-CH₂-CH₂- - - CH₂-NMeOH - Basic / Anion exchange resin (hydroxide form) - - CH₂-CH-CH₂-CH-CH₂- - - CH₂-NMeOH - **Process:** Hard H₂O is passed through cation exchange column which removes all cations (Ca⁺², Mg⁺²) from it & equivalent amount of H⁺ ions are released from this column to H₂O -