By Shukla Dhaval
Introduction
The hardness of water and its quality affect many industrial operations. Water supports life and serves many technical uses. Industries depend on clean water for reliable processes.Water quality shapes equipment life and product standards. Poor quality water creates scaling, corrosion, and process issues. Engineers study water properties before using it.Natural water contains dissolved salts, gases, and particles. These materials influence chemical behavior and usability. Careful analysis helps improve industrial performance.This article explains water sources, impurities, and the hardness of water in detail. It also explains industrial applications and treatment needs. Clear knowledge supports efficient water use.
Importance of Water
Water supports biological systems and many human activities. Living organisms depend on it for survival and health. Agriculture and industry also rely on steady water supply.About eighty percent of the earth surface contains water. Only a small portion remains suitable for direct human use. This limited share must support homes and industries.Industrial growth increases demand for reliable water sources. Clean water improves equipment life and process stability. Efficient management protects resources and supports sustainability.
Sources of Water
Natural water appears in several forms across the environment. Each source contains different mineral and chemical properties. Engineers study these sources during water treatment planning.Surface water remains the most visible source of water. Rivers, lakes, and reservoirs store large water volumes. Seasonal rain controls their supply.Underground water flows through soil layers and rock formations. Wells and springs provide access to this stored resource. Groundwater often contains dissolved minerals.
Rainwater forms through the natural water cycle. It offers low mineral content before contact with soil. Storage systems collect rain for domestic and industrial use.Sea water and estuarine water cover large parts of the planet. High salt concentration limits direct industrial use. Desalination plants treat this water for special purposes.
Types of Impurities Found in Water
Natural water always contains impurities from soil and atmosphere. These impurities influence taste, color, and chemical behavior. Treatment methods remove unwanted materials.
Dissolved Impurities
Dissolved impurities consist mainly of inorganic salts and gases. Minerals dissolve in water during underground movement. These dissolved ions create hardness and chemical changes.
(a) Inorganic salts e.g.,
(i)Cations:
`left(Caright)^{2+}`,`left(Mgright)^{2+}`,`left(Naright)^{+}`,`left(Kright)^{+}`,`left(Feright)^{2+}` `left(AIright)^{3+}`
and sometimes traces of
`left(Znright)^{2+}`,`left(Curight)^{2+}`
(ii) Anions:
`left(Clright)^-`,`left(So_4right)^{-2}`,`left(No_3right)^-`,`left(HCo_3right)^-`
and sometimes
`left(No_3right)^-`,`left(Fright)^-`
(b) Gases e.g.,`Co_2`,`O_2`,`N_2` oxides of `N_2` and sometimes `NH_3`,`H_2S`
(c) Organic salts
Suspended Impurities
Suspended impurities include visible particles carried by water flow. Clay, sand, and silt often appear in surface water. Industrial treatment removes these particles through filtration.Organic particles may include plant matter and oil droplets. These substances create turbidity and odor. Treatment plants remove them through settling and filtration.
Colloidal Impurities
Colloidal particles remain suspended due to small particle size. Clay and silica commonly appear in colloidal form. Coagulation helps remove them from water.Organic acids and proteins also form colloidal substances. These materials affect water color and taste. Chemical treatment improves clarity.
Bacterial Impurities
Natural water often carries microorganisms and bacteria. Some organisms affect water safety and hygiene. Disinfection removes harmful microbes.
Industrial Water Quality Requirements
| Purpose | Specifications and Remark |
|---|---|
| Paper Industry | (a) Free from alkalinity (alkaline water consumes more alum, thereby increasing the cost of production). |
| (b) Free from hardness: (Calcium and magnesium salts increase the ash content of the paper produced). | |
| (c) Free from colour, turbidity and salts of Fe and Mn : (colour and brightness of the paper are affected by the above impurities). | |
| (d) Free from Silica : (Silica causes cracks in the paper). | |
| Textile industry | (a) Free from turbidity : (turbidity causes uneven dyeing). |
| (b) Free from colour, and salts of Fe and Mn : (these impurities cause stains on the fabric). | |
| (c) Free from hardness and organic matter : (Hard water reduces the solubility of acidic dyes and causes precipitation of basic dyes. They also render the dyeing non-uniform. Organic matter may cause foul smell of the product). | |
| Thermal Power Generation industry | (a) Boiler feed Water : Free from hardness : (hard water causes scaleformation on boiler metal surface, thereby reducing heat transfer efficiency and causing shut-down or even accidents). |
| (b) Cooling water : The water should be non-scale forming, non-corrosive, and should not permit the growth of algae. Scale and algae reduce the heat transfer efficiency and interfere with free flow of water. | |
| Dairy industry | The water should be colourless, odourless, and tasteless. It should be free from pathogenic organisms. |
| Beverage industry | The water should be pure. It should not be alkaline, because alkalinity in water tends to neutralise the fruit acids and distorts the taste. |
| Laundry | The water should be free from colour, hardness and salts of Fe and Mn : (Hardness of water increases the consumption of soaps and detergents. Fe and Mn salts impart undesirable colour to the fabric. |
| Ice making, brewing, canning and distillery industry | Free from hardness and bacteria. |
Hardness of Water
The hardness of water refers to the presence of dissolved mineral salts. Calcium and magnesium ions mainly cause this property. Hard water forms little lather with soap.Soft water produces rich foam when mixed with soap. Hard water reacts with soap and forms insoluble scum. This reaction reduces cleaning efficiency.
`2C_{17}H_{35}COONa+CaCl_2rightarrowleft(C_{17}H_{35}COOright)_2Ca+2NaCl`
Metal ions such as `Fe^{+2}`, `Mn^{+2}` and `Al^{+3}` also react with soap. These ions may exist in smaller quantities in natural water. Their presence still contributes to hardness.
Degree of Hardness
Hardness is expressed as calcium carbonate equivalent concentration. Calcium carbonate provides a convenient standard reference. Engineers compare water quality using this unit.Hardness level indicates mineral content of water. High hardness values require treatment before industrial use. Boilers and cooling systems require low hardness water.
Types of Hardness
Temporary Hardness
Temporary hardness arises from calcium and magnesium bicarbonates. Heating water breaks these compounds into insoluble materials. Solid particles separate during boiling.
`\left(C_aHC_o3\right)\rightarrow\left(\triangle C_aCO_3+H_2O+CO_2M_gHCO_{32}\right)\rightarrow\left(\triangle M_gOH_2\right)`
Boiling water converts bicarbonates into carbonate deposits. Filtration removes these deposits easily. This treatment reduces hardness effectively.
Permanent Hardness
Permanent hardness arises from chlorides and sulphates of calcium and magnesium. These salts remain stable during heating. Boiling cannot remove them.Chemical softening methods remove permanent hardness. Treatment uses lime, soda ash, or ion exchange methods. Industrial plants apply these techniques widely.
Total Hardness = Temporary Hardness + Permanent Hardness
Units of Hardness
Water hardness uses several measurement units across engineering fields. These units express mineral concentration clearly. Scientists compare water samples through these units.
1. Parts per million (ppm)
2. Milligrams per liter (mg/L)
3. Degree french (°Fr)
4. Degree Clark (°Cl)
Parts per million (ppm)
It represents calcium carbonate equivalent in one million parts of water. Engineers commonly use this unit for water testing.
∴1 ppm = 1 part of `CaCo_3` equivalent hardness of `10^6` parts of `H_2O`
Milligrams per litre (mg/L)
It expresses milligrams of calcium carbonate equivalent per litre of water.
∴1 mg/L = 1 mg of `CaCo_3` equivalent per `10^6` mg of water
= 1 part of `CaCo_3` equivalent per `10^6` parts of water
= 1 ppm
Degree French (°Fr)
It expresses calcium carbonate equivalent in one hundred thousand parts of water.
∴1°Fr = 1 part of `CaCo_3` equivalent hardness per `10^5` parts of water
Degree Clark (°Cl)
This unit measures grains of calcium carbonate equivalent per gallon of water.
∴1°Cl = 1 parts of `CaCo_3` equivalent hardness per 70,000 parts of water.
Industrial Applications of Water
Industries rely on water for many technical processes. Water serves as coolant, solvent, and cleaning medium. Process efficiency depends on water quality.
Power Generation
- Used for steam production in thermal power plants
- Drives turbines to generate electricity
- Supports cooling systems
Chemical Industry
- Acts as reaction medium
- Supports dilution and purification
- Used in manufacturing chemicals
Construction Industry
- Used in mixing concrete and cement
- Essential for curing structures
- Controls dust during construction
Pharmaceutical Industry
- Used in drug preparation
- Cleaning equipment
- Production of purified water
Textile Industry
- Dyeing fabrics
- Bleaching materials
- Steam generation
Automotive and Metal Industries
- Cooling heavy machinery
- Metal quenching
- Surface cleaning
Conclusion
The hardness of water influences many industrial processes and equipment life. Proper water treatment improves operational efficiency. Engineers study water chemistry before industrial use.Knowledge of water sources, impurities, and hardness supports better process design. Careful water management protects equipment and environment. Industries depend on responsible water usage.