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1st Sem Hotel Engg. Notes

Hardness of water, water softening, Base Exchange Method

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Last updated: 4 July 2023

Total hardness is a test for overall water quality. There is no health concern associated with it. The degree of hardness is generally defined as calcium carbonate, equivalent of calcium and magnesium ions, present in water and is expressed in mg/L. In simple terms, hardness is a measure of how much calcium (and to a much lesser extent, magnesium) is in the water. Water hardness industry measures it in grains per litre, where 1 grain/litre = 64.72 mg/L.

 Hardness of water

The hardness of water is mainly due to the presence of dissolved bicarbonate (HCO3–), chloride (Cl–), and sulphate (SO42-), salts of calcium (Ca), magnesium (Mg), and iron (Fe). Sodium (Na) salts do not cause any hardness. All these salts that causes hardness come from the rocks, get dissolved in the groundwater by way of rainwater percolating through the rock.

Ordinary soaps are mainly sodium and potassium salts of organic fatty acids such as stearic acid, palmitic acid, and oleic acid. When soap is added to hard water, calcium and magnesium salts dissolved in water reacts with the salts in the soap and form insoluble scum. The reaction occurs-

Na/K stearate/palmitate + Ca/Mg salt → Ca/Mg stearate/palmitate + Na salt

           (soap salt)          (hard water salt)             (insoluble scum)

No soap in the mixture (mixture of hard water and soap) will form lather till all the salts present in the hard water are removed as scum. Thus soap is consumed without producing lather needed for cleaning clothes, resulting in a great wastage of costly soap. Synthetic detergents can overcome this problem as they form soluble salts of Ca and Mg and do not form a scum or soap curd.

Types of hardness

Depending upon the nature of the dissolved salts, hardness may be

  1. Temporary or carbonate hardness
  2. Permanent or noncarbonate hardness

Temporary hardness–        It is caused by the presence of dissolved bi-carbonates of calcium    [Ca (HCO3)2].

Permanent hardness– It is caused by the presence of chloride and sulphate salts of calcium and magnesium like, calcium chloride (CaCl2), calcium sulphate (CaSO4), magnesium chloride (MgCl2) and magnesium sulphate (MgSO4)

The reduction or removal of hardness from water is known as water softening. It is done mainly for the reduction in soap consumption, lowering the maintenance cost of plumbing fixture, boiler tubes, and to improve the taste of food, etc. and saving energy.

The permissible hardness for public supplies normally ranges 75 to 115 mg/L (14.25 mg/L is equivalent to one degree of hardness. Different methods for removal of hardness are shown below:-

                                                          Removal of hardness

           1.  Temporary hardness            2.    Both temporary and                      3. Permanent hardness

        ( Boiling        Clarke’s process )            ( permanent hardness)                    (  Washing soda)

                                         ↓ 

       Zeolite or Permutit        Lime          Caustic soda           Ion exchange            Calgon

        (base exchange)           soda                                             (by resin)                 (process)

                                                                         Process

 

The temporary hardness of water can be removed either by boiling or by adding lime to the water. The chemical reaction takes place (in boiling process) as

Ca(HCO3)2    +    Heat  →  CaCO3 ↓       + CO2 ↓      + H2O

(Calcium                           (Calcium

bicarbonate)                    carbonate, insoluble)

Mg(HCO3)2    +    Heat  →  MgCO3 ↓       + CO2 ↓      + H2O

(Magnesium  bicarbonate, insoluble)

The chemical reaction takes place (in addition of lime or Clarke’s process) as

Ca(HCO3)2          +         Ca(OH)2          →        2CaCO3  ↓    +     2H2O

(Calcium                      (Hydrated lime)              (Calcium

bicarbonate)                                                         carbonate, insoluble)

Mg(HCO3)2          +         2Ca(OH)2          →      Mg(OH)2 ↓   +    2CaCO3  ↓    +     2H2O

There are six methods for removing permanent hardness like,

  1. Washing soda process
  2. Base exchange process (or Zeolite process)
  3. Lime soda process
  4. Caustic soda process
  5. Ion-exchange process or demineralization(DM) process
  6. Calgon process

 

  1. The chemical formula of washing soda is Na2CO3. The reaction takes place when washing soda is added to hard water is

         Na2CO3    +      CaSO4             →              CaCO3 ↓    +        Na2SO4

         Na2CO3    +      MgCl2              →              MgCO3 ↓    +        2NaCl

  1. Hardness can be very effectively and economically removed by using a chemical called zeolite. A zeolite softener resembles a sand filter. The hard water enters the softener from top react with the zeolite and the softened water is collected through the strainer at the base. The reaction takes place as

      Na2Z              +        Ca or Mg salt       →           Na2 salt     +     Ca or Mg zeolite

(Sodium zeolite/            (Hard water salt)                                        (Exchanged or used

  Or active zeolite)                                                                                  zeolite)

  • 6  –

After a few days of operation, all the active sodium zeolite changes to used calcium and magnesium zeolite. These can be converted back to the active sodium zeolite by reacting it with 10 per cent solution of sodium chloride (common table salt solution). This process is known as regeneration. The reaction takes place as

CaZ / MgZ        +          2NaCl              →           Na2Z              +         CaCl2 / MgCl2

 (used zeolite)          (sodium chloride              (regenerated              (dissolved salt removed by

                                          Solution)                    zeolite)                     flushing water)

Advantages of zeolite process- * Zero hardness can be obtained and have specific uses in textile industries, boilers, etc. * The plants are compact, automatic, and easy to operate. * The running ,maintenance and operation (RMO) cost is quite less. * It also removes iron and manganese from water. * There is no problem in treating water of varying quality.

  1. In lime soda process, in addition to washing soda lime is added to remove temporary hardness. Hydrated lime reacts with bicarbonates of Ca and Mg.
  2. Caustic soda can be used to remove both carbonate (temporary) and non-carbonate (permanent) hardness. This process is very efficient for low alkalinity water. Calcium and magnesium hydrogen carbonates react with caustic soda to produce insoluble calcium carbonate and magnesium hydroxide. The reactions are-

2NaOH         +        MgSO4           →         Mg (OH)2   ↓        +      Na2SO4       

            2NaOH         +         CaCl2            →          Ca (OH)2   ↓         +      2NaCl  

            4NaOH         +        Mg (HCO3)2   →         Mg (OH)2   ↓        +      2Na2CO3    + 2H2O      

            2NaOH         +        Ca (HCO3)2   →         CaCO3   ↓       +      2Na2CO3    +   H2O 

  1. There are many types of equipment in industry like water boiler, other process equipment and scientific apparatus water boiler and other  to produce insoluble calcium carbonate and magnesium hydroxid  which need water free of minerals. The process by which the minerals are removed is known as demineralization (DM) and the plant is known as DM plant. It is very suitable for producing water of any desired hardness or even mineral free water. The demineralized water is sometimes called deionized water and is as pure as distilled water.

The process consists of passing the water through cat ion exchange resins, which produce almost similar effects as are produced in the zeolite process, except that hydrogen (instead of sodium) is exchanged for the basic metallic ions. The cat ion exchange resins

 

  • 7  –

in fact are phenol aldehyde condensation products whose chemical formula is H2R (H represents hydrogen ion and R represents the organic part of the substance).  The reaction takes place as below:-

Ca (HCO3)2         +         H2R              →            CaR           +       2H2O       +    2CO2   ↑

                                   (fresh cat ion                (exchanged or

                                     exchange resin)            used resin)

Na2CO3           +         H2R              →              Na2R          +          H2O        +      CO2   ↑

  1. Calgon is the trade name of a complex salt, sodium hexametaphosphate (NaPO3)6. Calgon ionizes to give a complex anion, which subsequently combines with Ca and Mg ions in hard water.

(NaPO3)6   or   Na2 (Na4P6O18)         →         2Na+        +          Na4P6O182

(complex anion)

In addition of Calgon to hard water causes the calcium and magnesium ions of hard water to displace sodium ions from the anion of Calgon according to the following reaction:

CaSO4        +       Na2 (Na4P6O18)      →        Na2SO4        +        Ca (Na4P6O18)

This result in the removal of calcium and magnesium ions from hard water in the form of a complex compound with Calgon and thus the water softened. Sodium salts are released into water without causing any hardness. It is being dosed into water used for washing machine, dyeing work, etc.

 

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Syllabus BHM106

01 Maintenance

  1. Introduction
  2. Preventive and breakdown maintenance, comparisons
  3. Role & Importance of maintenance department in the hotel industry with emphasis on its relation with other departments of the hotel.
  4. Organization chart of maintenance department, duties and responsibilities of maintenance department

02 Fuels used in the catering industry

  1. Introduction
  2. Types of fuel used in catering industry; calorific value; comparative study of different fuels
  3. Calculation of amount of fuel required and cost.

03 Gas

  1. Introduction
  2. Heat terms and units; method of transfer
  3. LPG and its properties; principles of Bunsen burner, precautions to be taken while handling gas; low and high-pressure burners and their corresponding heat output
  4. Gas bank, location, different types of manifolds

04 Electricity

  1. Introduction
  2. Fundamentals of electricity, insulators, conductors, current, potential difference resistance, power, energy concepts; definitions, their units and relationships, AC and DC; single phase and three phases and its importance on equipment specifications
  3. Electric circuits, open circuits and close circuits, symbols of circuit elements, series and parallel connections, short circuits, fuses; MCB, earthing, the reason for placing switches on the live wire side.
  4. Electric wires and types of wiring
  5. Calculation of electric energy consumption of equipment, and safety precautions to be observed while using electric appliances.
  6. Types of lighting, different lighting devices, incandescent lamps, fluorescent lamps, other gas-discharged lamps, illumination, and units of illumination.
  7. External lighting
  8. Safety in handling electrical equipment

05 Water systems

  1. Introduction
  2. Water distribution system in a hotel
  3. Cold water systems in India
  4. Hardness of water, water softening, base exchange method
  5. Cold water cistern swimming pools
  6. Hot water supply system in hotels
  7. Flushing system, water taps, traps and closets.

06 Refrigeration & Air-conditioning

  1. Basic principles, latent heat, boiling point and its dependence on pressure, vapour compressor system of refrigeration and refrigerants.
  2. Vapour absorption system, care and maintenance of refrigerators, defrosting, types of refrigerant units, their care and maintenance.
  3. Conditions for comfort, relative humidity, humidification, dehumidifying, due point control, unit of air conditioning
  4. Window type air conditioner, central air conditioning, preventive maintenance
  5. Vertical transportation, elevators, escalators

07 Fire prevention and fire fighting system

  1. Classes of fire, methods of extinguishing fires (Demonstration)
  2.  Fire extinguishers, portable and stationery
  3.  Fire detectors and alarm
  4. Automatic fire detectors cum extinguishing devices
  5. Structural protection
  6. Legal requirements

08 Waste disposal and pollution control

  1. Solid and liquid waste, sullage and sewage, disposal of solid waste
  2.  Sewage treatment
  3. Pollution related to the hotel industry
  4. Water pollution, sewage pollution
  5. Air pollution, noise pollution, thermal pollution
  6. Legal Requirements

09 Safety

  1. Accident prevention
  2. Slips and falls
  3. Other safety topics

10 Security

11 Equipment replacement policy

  1. Introduction
  2. Circumstances under which equipment are replaced.
  3. Replacement policy of items which gradually deteriorates
  4. Replacement when the average annual cost is minimum
  5. Replacement when the present cost is minimum
  6. The economic replacement cycle for suddenly failing equipment

12 Audio-visual equipment

  1. Various audio-visual equipment used in hotel
  2. Care and cleaning of an overhead projector, slide projector, LCD and PowerPoint presentation units
  3. Maintenance of computers
  4. Care and cleaning of PC, CPU, Modem, UPS, Printer, Laptops
  5. Sensors – Various sensors used in different locations of a hotel – type, uses and cost-effectiveness

13 Contract maintenance

  1. Introduction
  2. The necessity of contract maintenance, advantages and disadvantages of contract maintenance
  3. Essential requirements of a contract, types of contract, their comparative advantages and disadvantages.
  4. Procedure for inviting and processing tenders, negotiating and finalizing