Unit 3
Q1. Describe the following:
(a) Coliforms as indicators of fecal pollution
(b) Nuisance microorganisms in water
(c) MPN as quantitative method
(d) Purification of potable water
(a) Coliforms as Indicators of Fecal Pollution
Introduction:
Coliforms are a group of bacteria commonly found in the intestines of warm-
blooded animals, including humans. Their presence in water is a strong indicator
of fecal contamination. Coliforms are used as indicators because their presence
suggests the possible presence of harmful pathogens that can cause diseases.
Characteristics of Coliforms:
Total Coliforms: These are a broad group of bacteria found in the
environment, including soil, water, and the intestines of warm-blooded
animals.
Fecal Coliforms (e.g., Escherichia coli): These are specifically found in the
intestines of humans and other warm-blooded animals. Their presence in
water indicates recent fecal contamination.
Importance in Water Quality Monitoring:
Coliform bacteria are used as an indicator organism because they are easy to
detect and can be found in much higher numbers than pathogens.
While coliforms themselves may not be harmful, their presence suggests that
water may be contaminated with pathogenic organisms such as Salmonella,
Shigella, or Enterococcus, which cause gastrointestinal diseases.
Coliform Test Methods:
Unit 3 1
, Membrane Filter (MF) Method
Multiple Tube Fermentation (MTF) Method
Colilert Method (using a reagent-based test)
(b) Nuisance Microorganisms in Water
Introduction:
Nuisance microorganisms are non-pathogenic organisms that may not cause
disease but are considered undesirable due to their impact on water quality,
aesthetics, and ecosystem health. These microorganisms can lead to problems in
water distribution systems, as well as in recreational waters.
Examples of Nuisance Microorganisms:
1. Algae (e.g., Cyanobacteria):
Algal blooms in water bodies can create taste and odor problems and
deplete oxygen in the water, leading to hypoxia.
Some algae produce toxins (e.g., cyanotoxins), which can affect aquatic
life and human health.
2. Protozoa (e.g., Acanthamoeba):
Protozoa can cause infections, though they are often more of a nuisance
than a threat.
Acanthamoeba is particularly a concern in recreational waters and water
systems.
3. Slime-forming Bacteria (e.g., Pseudomonas spp., Sphaerotilus):
These bacteria form biofilms in pipes, affecting water flow and the
efficiency of water treatment processes.
They can contribute to corrosion and clogging in water distribution
systems.
4. Iron and Sulfur Bacteria:
These microorganisms oxidize iron or sulfur, leading to the formation of
deposits of iron oxide (rust) or sulfur compounds, which can cause
staining and clogging in pipes.
Unit 3 2
, (c) MPN as Quantitative Method
Introduction:
The Most Probable Number (MPN) method is a statistical technique used to
estimate the concentration of microorganisms in water. It is particularly used for
determining the presence and abundance of coliform bacteria in water samples,
which is important for assessing fecal contamination.
Principle of the MPN Method:
The MPN method relies on inoculating a series of test tubes or wells with
different dilutions of a water sample. Each tube or well contains a nutrient
medium that supports the growth of coliform bacteria.
After incubation, the number of tubes or wells showing gas production
(indicating bacterial growth) is recorded. The MPN index is determined from
this pattern of growth and the number of positive results in each dilution.
Steps Involved:
1. Preparation: A series of dilutions of the water sample is prepared.
2. Inoculation: Each dilution is added to a set of test tubes containing a specific
medium (usually Lactose Broth for coliforms).
3. Incubation: The test tubes are incubated, and the tubes are checked for gas
production or other signs of bacterial growth.
4. Results Interpretation: The results are compared with standard MPN tables to
estimate the concentration of coliforms in the original sample.
Advantages:
Simple and inexpensive.
Effective for detecting low levels of coliform bacteria in drinking water.
Limitations:
Less accurate than direct counts (e.g., plate counts).
Requires careful interpretation and comparison with MPN tables.
(d) Purification of Potable Water
Unit 3 3
, Introduction:
The purification of potable water involves processes to remove impurities,
pathogens, and undesirable substances, ensuring that water is safe for human
consumption. The primary goals of water purification are to make water free from
harmful microorganisms and reduce the presence of chemicals, heavy metals,
and other pollutants.
Steps in the Water Purification Process:
1. Coagulation and Flocculation:
Coagulation involves the addition of chemicals (e.g., alum or ferric
chloride) to the water, which neutralize the charges of suspended
particles (like dirt and organic matter).
Flocculation follows coagulation, where the coagulated particles (flocs)
form larger aggregates that are easier to remove.
2. Sedimentation:
After coagulation, the water is allowed to sit in large tanks so that the
heavy flocs can settle to the bottom.
3. Filtration:
The water is passed through sand filters, activated charcoal, or other
filtering materials to remove smaller particles and some dissolved
impurities.
This step is essential for removing remaining turbidity and
microorganisms.
4. Disinfection:
Chlorine, ozone, or ultraviolet (UV) light is used to kill or inactivate any
remaining pathogens, including bacteria, viruses, and protozoa.
Chlorination is the most common method of disinfection, where chlorine
(Cl2) is added to water:
Cl2 + H2O → HCl + HOCl (Hypochlorous acid, which is the disinfecting
agent).
5. Storage:
Unit 3 4
Q1. Describe the following:
(a) Coliforms as indicators of fecal pollution
(b) Nuisance microorganisms in water
(c) MPN as quantitative method
(d) Purification of potable water
(a) Coliforms as Indicators of Fecal Pollution
Introduction:
Coliforms are a group of bacteria commonly found in the intestines of warm-
blooded animals, including humans. Their presence in water is a strong indicator
of fecal contamination. Coliforms are used as indicators because their presence
suggests the possible presence of harmful pathogens that can cause diseases.
Characteristics of Coliforms:
Total Coliforms: These are a broad group of bacteria found in the
environment, including soil, water, and the intestines of warm-blooded
animals.
Fecal Coliforms (e.g., Escherichia coli): These are specifically found in the
intestines of humans and other warm-blooded animals. Their presence in
water indicates recent fecal contamination.
Importance in Water Quality Monitoring:
Coliform bacteria are used as an indicator organism because they are easy to
detect and can be found in much higher numbers than pathogens.
While coliforms themselves may not be harmful, their presence suggests that
water may be contaminated with pathogenic organisms such as Salmonella,
Shigella, or Enterococcus, which cause gastrointestinal diseases.
Coliform Test Methods:
Unit 3 1
, Membrane Filter (MF) Method
Multiple Tube Fermentation (MTF) Method
Colilert Method (using a reagent-based test)
(b) Nuisance Microorganisms in Water
Introduction:
Nuisance microorganisms are non-pathogenic organisms that may not cause
disease but are considered undesirable due to their impact on water quality,
aesthetics, and ecosystem health. These microorganisms can lead to problems in
water distribution systems, as well as in recreational waters.
Examples of Nuisance Microorganisms:
1. Algae (e.g., Cyanobacteria):
Algal blooms in water bodies can create taste and odor problems and
deplete oxygen in the water, leading to hypoxia.
Some algae produce toxins (e.g., cyanotoxins), which can affect aquatic
life and human health.
2. Protozoa (e.g., Acanthamoeba):
Protozoa can cause infections, though they are often more of a nuisance
than a threat.
Acanthamoeba is particularly a concern in recreational waters and water
systems.
3. Slime-forming Bacteria (e.g., Pseudomonas spp., Sphaerotilus):
These bacteria form biofilms in pipes, affecting water flow and the
efficiency of water treatment processes.
They can contribute to corrosion and clogging in water distribution
systems.
4. Iron and Sulfur Bacteria:
These microorganisms oxidize iron or sulfur, leading to the formation of
deposits of iron oxide (rust) or sulfur compounds, which can cause
staining and clogging in pipes.
Unit 3 2
, (c) MPN as Quantitative Method
Introduction:
The Most Probable Number (MPN) method is a statistical technique used to
estimate the concentration of microorganisms in water. It is particularly used for
determining the presence and abundance of coliform bacteria in water samples,
which is important for assessing fecal contamination.
Principle of the MPN Method:
The MPN method relies on inoculating a series of test tubes or wells with
different dilutions of a water sample. Each tube or well contains a nutrient
medium that supports the growth of coliform bacteria.
After incubation, the number of tubes or wells showing gas production
(indicating bacterial growth) is recorded. The MPN index is determined from
this pattern of growth and the number of positive results in each dilution.
Steps Involved:
1. Preparation: A series of dilutions of the water sample is prepared.
2. Inoculation: Each dilution is added to a set of test tubes containing a specific
medium (usually Lactose Broth for coliforms).
3. Incubation: The test tubes are incubated, and the tubes are checked for gas
production or other signs of bacterial growth.
4. Results Interpretation: The results are compared with standard MPN tables to
estimate the concentration of coliforms in the original sample.
Advantages:
Simple and inexpensive.
Effective for detecting low levels of coliform bacteria in drinking water.
Limitations:
Less accurate than direct counts (e.g., plate counts).
Requires careful interpretation and comparison with MPN tables.
(d) Purification of Potable Water
Unit 3 3
, Introduction:
The purification of potable water involves processes to remove impurities,
pathogens, and undesirable substances, ensuring that water is safe for human
consumption. The primary goals of water purification are to make water free from
harmful microorganisms and reduce the presence of chemicals, heavy metals,
and other pollutants.
Steps in the Water Purification Process:
1. Coagulation and Flocculation:
Coagulation involves the addition of chemicals (e.g., alum or ferric
chloride) to the water, which neutralize the charges of suspended
particles (like dirt and organic matter).
Flocculation follows coagulation, where the coagulated particles (flocs)
form larger aggregates that are easier to remove.
2. Sedimentation:
After coagulation, the water is allowed to sit in large tanks so that the
heavy flocs can settle to the bottom.
3. Filtration:
The water is passed through sand filters, activated charcoal, or other
filtering materials to remove smaller particles and some dissolved
impurities.
This step is essential for removing remaining turbidity and
microorganisms.
4. Disinfection:
Chlorine, ozone, or ultraviolet (UV) light is used to kill or inactivate any
remaining pathogens, including bacteria, viruses, and protozoa.
Chlorination is the most common method of disinfection, where chlorine
(Cl2) is added to water:
Cl2 + H2O → HCl + HOCl (Hypochlorous acid, which is the disinfecting
agent).
5. Storage:
Unit 3 4
