Biochemical Oxygen Demand (BOD)

• Introduction

Waste water consist lots of undesirable things which are harmful for humans and others creatures.Harmful things may be Organic or Inorganic,to purify water we have to remove this hazards by oxidised those hazards with the help of microorganisms but for this oxidation we required some amount of oxygen. 

                     The amount of oxygen required to oxidised all the organic as well as inorganic matters is known as Oxygen Demand.

Full form of BOD is Biochemical Oxygen Demand.

• Definition

Oxygen required by the microorganisms to carryout biological decomposition of organic matters under aerobic conditions at standard temperature.

so BOD means the oxygen required only to remove organic wastes.

• Discussion

BOD is classified in two segment-

1. 1st stage BOD (Carbonaceous demand)

2. 2nd stage BOD (Nitrification demand )

Carbonaceous demand means oxygen required to oxidised Carbonaceous matters and Nitrification demand means oxygen required to oxidised Nitrogenous matters.

As the Carbonation starts first it known as 1st stage demand after completion of cardonation Nitrification starts.

See the graph it will be more clear-

• Some Important Points

1. Generally BOD is tasted for 5 days (BOD5).

2. BOD is calculated at a standard temperature of 20 degree celsius.

3. After 6-10 days of Carbonation Nitrification starts.

4. In BOD5 we generally find the Carbonaceous BOD means 1st stage BOD.

5. To get zero BOD it requires infinite time.

6. In 20 days almost 95-99 percent of organic matter oxidised.

• Relation Between DO(Dissolved Oxygen) and BOD

BOD5 (at 20 degree celsius) = [Initial DO - Final DO]x[Dilution factor] 

                                       ( We will discuss about DO and Dilution Factor Later for that Keep Visiting this site )

Water Logging

• Introduction

Water Logging refers to the saturation of soil with water.

It is a phenomena in which productivity of land gets affected due to rise in water table,thus leading to flooding of root zone of the plants.

• Cause

1. Inadequate surface drainage.

2. Seepage from canal system.

3. Over and intensive irrigation of field.

4. Heavy rainfall.

5. Submergence due to Flood.

6. Irregular topography.

• Effects

1. Inhibiting activity of soil bacteria.
2. Decrease in availability of Camilla water.
3. Rise in level of salt in the surface soil.
4. Reduction in productivity of crop.
5. Growth of wild flora which decrease in crop yielding.

• Remedial Measures for Controlling Water Logging

1. Lining of canal and water courses.

2. Reduction in intensity of irrigation.

3. Crop rotation.

4. Optimum use of  water.

5. Providing well drainage system.

6. Introduction of Lift irrigation.

                                                             (Special Thanks to Mr. Animesh Bhunia for his helping hand)

Standard Penetration test

• Introduction

It is the measurement of resistance to penetration of a sampling spoon ,a cone or other shaped tools under dynamic or static loading.by this test we get a penetration value (N) which helps in finding out the other properties of soil,particularly for cohesive soil.

The properties which we can find -

1. Angle of internal friction.

2. Density index.

3. Unconfined compressive Strength.

4. Consistency of soil.

• Specification of  Test Equipments  

1. A clean hole of  55mm to 150mm in diameter.

2. Split spoon sampler outer dia-50.8mm and inner dia-35mm.

3. A hamer of 63.5 kg.

• Procedure

1. The split tube sampler commonly known as split spoon  sampler,resting on the bottom of the bore hole is allowed to sink under its own weight. 

2. It is then seated 15 cm with the blows of the hammer falling through a height of 15 cm,there after the split spoon is further driven by 30cm .

3. The no of blows required after each 15 cm penetration is recorded.The first 15cm of drive may be considered to be Seating Drive. 

4. The total blows required for the second and tird 15cm of penetration is termed as the Penetration resistance N.   

If the split spoon sampler is driven less than 45 cm (total),then the penetration resistance

shall be for the last 30 cm of penetration.   

• Correction's Required 

After finding out the penetration value ( N ) we need to do two correction

1. Overburden Correction.

2. Dilatancy Correction.

          1.Overburden Correction-

The penetration resistance ( N ) in granular soil influenced by overburden pressure,after correcting the value,N value is given by N'.

           2. Dilatancy Correction-

Silty fine sands & fine sands below the water table developed pore water pressure which is not easily dissipated .The pore pressure increase the resistance to the soil & hence penetration.

So a correction is needed,we have to correct the value of  N' again and after correction N' is given by N''. 

Break Point Chlorination

• Introduction

Chlorine is a Disinfecting agent it is use in the process of water disinfection it helps in removing organic matters and harmful bacteria's from water.Chlorine enters in the cell walls of bacteria and kills the enzymes which are essential for their metabolic processes,and finally it destroy the bacteria and clean the water .

• Definition

Break point chlorination is the dose of chlorine should be added in water for disinfection process beyond which further addition of chlorine will appear as free residualchlorine.

Break point chlorination gives an idea about amount of chlorine required in disinfection process.

• Explanation

When we start adding chlorine in water this chlorine consumed in removing the Bacteria's and organic matter , so we need to add that amount of chlorine which can remove all the bacteria and organic matter.

Now when all the organic matters and bacteria removed, if we add further amount of chlorine in water this chlorine dose not involved in any chemical reaction and it appears as Free Residual Chlorine means it remains in its original form.

The point above which chlorine remain as Free Residual Chlorine is Break Point (See the graph- in graph point C is Break Point)

• Graph
  

Hardness of Water

• Definition

It is a property of water which resist the formation of foam in soap water.

• Cause

Presence of Bivalent cations of Calcium & Magnesium.

• Disadvantages

1. Hardness cause scaling in boiler.

2. Increase soap consumption.

3. Cause incrustation of supply pipes.

4. remove color from clothes.

• Types

There is two types of hardness- 

1. Temporary Hardness or Carbonate Hardness - Hardness caused due to presence of Carbonate & Bi-Carbonates of Calcium and Magnesium [ Ca(HCO3)2,MgCo3 etc]

2. Permanent or Non-Carbonate Hardness - Hardness caused due to presence of Sulfates,Chlorides & Nitrates of Calcium and Magnesium [ MgSO4, Mg(OH)2, CaSO4, CaCl2 etc]

• Softening

The removal of hardness from water by various standard methods is known as Softening of water.

• Method's of Temporary Hardness removal

1. Boiling of  Water.

2. Addition of Lime in water.

• Methods of Permanent Hardness Removal

1. Lime Soda Process.

2. Zeolite method or Base exchange method.

3. Ion Exchange method 

• Important Notes for Competitive Exams  

1. Only Zeolite Method Can Gives us Zero Hardness.

2. Na ions do not cause hardness.
3. Some Tri-valent Cations also cause hardness like Al and Fe .

• Numerical problem 

Continuity of a Function

A function f(x) is said to be continuous at a point  x=a if,
   
                   Point value = Left hand limit (LHL)= Right hand limit (RHL)

what is point value - it is the value of a function at a particular point, as here the value of                                                f(x)  at  x=a  is  f(a)  so f(a) is the point value of  f(x) at a .

what is LHL & RHL - see the graph let y=f(x) is continuous at x=a , now LHL is a point                                                    whose value  is slightly less than a  means [a-h] ,RHL is a point                                                           whose value is slightly greater than  a means [a+h].

Let us understand mathematically (see the graph),

let f(x) is a function,it will be continuous at x=a only when ,
         
                                       f(a) [point value] = f(a-h) [LHL] = f(a+h) [RHL]

h is a small quantity which tends to zero.

  

(A special Thanks to Mr. Animesh Bhunia for his helping hand )

What is Turbidity

Turbidity is a Physical characteristics of water.

• Definition

It is the property of water by means of which light is scattered at right angle to the incident light beam when the pass through the water, due to the presence of suspended particle in it.

          Turbidity depends upon the presence of suspended particle in the water.

• Measuring Devices

1. Turbidity rod

2. Jackson's Turbidity Meter

3. Bayli's Turbidity Meter 

4. Modern Nephlometer

• Measuring Units

1. NTU ( Nephelometric Turbidity Unit )

2. JTU ( Jackson Turbidity Unit )

3. FTU ( Formazin Turbidity Unit )

• Permissible Limit 

10 to 25 NTU for drinking water

• NOTE

JTU is equal to the turbidity produced by 1mg Sio2 in 1Lt of  distilled water.

FTU is equal to the turbidity produced by 1mg Formazin in 1Lt of  distilled water.

Water Quality

Water Quality Refers to the Chemical,Physical and Biological Characteristics Of water.

Chemical Characteristics :

   

    1. pH

    2. Acidity

    3. Alkanity

    4. Hrdness

    5. Fluoride Content

    6. Chloride Content

    7. BOD ( Biochemical Oxygen Demand )

    8. COD ( Chemical Oygen Demand )

Physical Characteristics

     

     1. Turbidity

     2. Colour

     3. Taste & Odour

     4. Temperature

     5. Suspended Solid

     6. Conductivity

Biological Parameters

     1. Pathogenic,Bacteria,Micro-organism

     2. Non-pathogenic/Coliform