Chapter 1


Q:-What is Water Treatment?
Ans:-Water treatment is any process that makes water more acceptable for a specific end-use. The end use may be drinking, industrial water supply, irrigation, river flow maintenance, water recreation or many other uses, including being safely returned to the environment.

Introduction:-The more common processes used in potable water treatment are the chemical and physical processes. Biological processes are primarily used for treatment of wastewater. ... The biological activated carbon (BAC) process is also a biological process that is used to remove organic contaminants from potable water.

Characteristics imparted by impurities in water:-The temperature of water affects some of the important physical properties and characteristics of water: thermal capacity, density, specific weight, viscosity,surface tension, specific conductivity, salinity and solubility of dissolved gases and etc..Water impurities include dissolved and suspended solids. Calcium bicarbonate is a soluble salt. A solution of calcium bicarbonate is clear, because the calcium and bicarbonate are present as atomic sized ions which are not large enough to reflect light. Some soluble minerals impart a color to the solution. Soluble iron salts produce pale yellow or green solutions; some copper salts form intensely blue solutions. Although colored, these solutions are clear.

Q:-What is Hardness Of Water?

Ans:-Water Hardness The amount of dissolved calcium and magnesium in the water. The simple definition of water hardness is the amount of dissolved calcium and magnesium in the water. Hard water is high in dissolved minerals, both calcium and magnesium.

Types of Hardness of Water

Temporary hardness:

Hardness of water caused by the bicarbonates of calcium and magnesium is called temporary hardness. It can be removed by boiling the water. When water is boiled, the bicarbonates of calcium and magnesium decompose to form carbonates. These are insoluble and collect on the sides of the vessel as fur or scale. When calcium and magnesium bicarbonates are removed from the water, it becomes soft.

Permanent hardness:

Hardness caused by the sulphates and chlorides of calcium and magnesium is called permanent hardness, because it cannot be removed by boiling. To remove permanent hardness we have to resort to other methods such as treating the water with sodium carbonate or by passing hard water through ion exchangers, (you shall study about these in higher classes). Distilling the water removes both types of hardness. Distilled water is the purest form of water and the most expensive one!

Key Concept:-

  • Calcium and magnesium salts dissolved in water cause water hardness.
  • Water hardness can be measured using a titration with ethylenediaminetetraacetic acid (EDTA).

    The ionised form of EDTA is shown on the right.
    EDTA dissolved in water forms a colourless solution.

  • At pH 10, calcium and magnesium ions form colourless, water soluble, complexes with EDTA:

    calcium ion complexed by EDTA : CaEDTA2-
    magnesium ion complexed by EDTA : MgEDTA2-

  • An indicator, known as a metal ion indicator, is required for the titration.

    Eriochromshwartz-T (Erio T) is a suitable indicator.
    Eriochromshwartz-T is wine-red in hard water, but turns sky blue in the presence of free EDTA ions in the solution.

  • Endpoint of the titration is when all the Ca2+ and Mg2+ ions have been complexed by the EDTA.

    Before the endpoint, Ca2+ and Mg2+ are in excess, there is no free EDTA in solution.
    Immediately after the endpoint, there is an excess of EDTA.

  • It is essential that deionised water (water in which ions have been removed) is used in preparing all solutions, and in rinsing the conical flask.

    Ca2+ and Mg2+ ions must NOT be present in the water used to prepare the solutions, or in rinsing.

Q:-What is the main cause of hard water?

Ans:-Calcium and magnesium dissolved in water are the two most common minerals that make water "hard." The degree of hardness becomes greater as the calcium and magnesium content increases and is related to the concentration of multivalent cations dissolved in the water.

Q:-What is the total hardness of water?Ans:-Calcium and magnesium dissolved in water are the two most common minerals that make water "hard." The hardness of water is referred to by three types of measurements: grains per gallon, milligrams per liter (mg/L), or parts per million (ppm).

Q:-What Is Unit Of Hardness Of Water?

Ans:-Water hardness is often not expressed as a molar concentration, but rather in various units, such as degrees of general hardness (dGH), German degrees (°dH), parts per million (ppm, mg/L, or American degrees), grains per gallon (gpg), English degrees (°e, e, or °Clark), or French degrees (°fH, °F or °F; lowercase f is ...


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Q:- What is disadvantage of Hard Water?

Ans:-Disadvantages of Hard Water: ... It is very difficult to wash clothes with hard wateras it requires more soap and leaves a messy scum that cannot be washed out easily. When hard water is boiled at home or in industries, it leaves deposits of calcium and magnesium salts in kettles, hot-water pipes, boilers and radiators.

Q:-What Is Scale and sludge formation in boilers?

Ans:-Scale and sludge formation in boilers. In boilers, water evaporates continuously and the concentration of the dissolved salts increases progressively. When their concentrations reach saturation point, they are thrown out of water in the form of precipitates on the inner walls of the boiler.

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Q:-What Is Boiler corrosion?
Ans:-Boiler corrosion is the active destruction of soundboiler metal by the pitting action of dissolved oxygen in the boiler water. This usually results in deep holes in the metal which are self protected by furthercorrosion products ie scabs or blisters over the hole which allow the chemical reaction to continue.

Corrosion in Boiler:-Corrosion is the reversion of a metal to its ore form. Iron, for example, reverts to iron oxide as the result of corrosion. The process of corrosion, however is a complex electro chemical reaction and it takes many forms. Corrosion may produce general attach over a large metal surface or it may result in pinpoint penetration of metal. Corrosion is a relevant problem caused by water in boilers. Corrosion can be of widely varying origin and nature due to the action of dissolved oxygen, to corrosion currents set up as a result of heterogeneities on metal surfaces, or to the iron being directly attacked by the water.
Corrosion is caused principally by complex oxide-slag with low melting points. High temperature corrosion can proceed only if the corroding deposit is in the liquid phase and the liquid is in direct contact with the metal.
Corrosion is caused by the combination of oxide layer fluxing and continuous oxidation by transported oxygen.

Q:-What is Foaming and priming?
Ans:-Foaming and priming in boilers. Boiler water carry-over is the contamination of the steam with boiler-water solids. Bubbles or froth actually build up on the surface of the boiler water and pass out with the steam. This is called foaming and it is caused by high concentration of any solids in the boiler water.
Boiler water carry-over is the contamination of the steam with boiler-water solids. Bubbles or froth actually build up on the surface of the boiler water and pass out with the steam. This is called foaming and it is caused by high concentration of any solids in the boiler water. It is generally believed, however, that specific substances such as alkalis, oils, fats, greases, certain types of organic matter and suspended solids are particularly conducive to foaming. In theory suspended solids collect in the surface film surrounding a steam bubble and make it tougher. The steam bubble therefore resists breaking and builds up foam. It is believed that the finer the suspended particles the greater their collection in the bubble.

Q:-What is Softening methods?

Ans:-Water softening is the removal of calcium, magnesium, and certain other metal cations in hard water. The resulting soft water is more compatible with soap and extends the lifetime of plumbing. Watersoftening is usually achieved using lime softening or ion-exchange resins.

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