Microbiology of domestic and sewage water

Microbiology of
Domestic and
Sewage Water

Domestic Water
Domestic water of most communities and municipalities comes from
surface sources rives stream and lakes. Such water supplies are likely
to be contaminated with Domestic industrial and agricultural waste.
Many of the times this polluted water is being used by people in many
ways. As we know in water cycle the water is reused again and again
as its part of nature we also can reuse water over many times but that
water which is not contaminated.
Also the growth in population and vast needs of water has made new
dimension of water reuse and “speed up” the natural process of water
recycling and to ensure a safe water supply.
That’s’ why there is growing interest in developing acceptable methods
for water reuse more quickly.
Comprehensive federal legislation has also been developed enforce
stringent regulations, designed to reduce water pollution and improve
water quality.

Pollution
Water could be perfectly clear , colorless and tasteless and
yet be unsafe to drink. Contaminants that pollute water are
of three types:
1. Chemical
2. Physical
3. Biological
Our discussion is based on Biological contaminants. Water
having pathogenic microbes causes several diseases and
most of these are intestinal. From urine or feces of infected
person they enter water bodies to infect other organisms. To
prevent these to become part of water there must be
1. Water Purification Method
2. Treatment of waste water before reuse
3. Procedures to detect microbes present in water

1. Water Purification :
Water which is safe to drink is free-of disease causing agents and
chemical substances harmful to health and is called POTABLE WATER.
NON POATABLE on the other hand is that which is not purified for
human use.
Purification methods vary according to source of water and amount of
water needed.
Single Dwelling Water Supplies :
Underground sources----Wells and springs------provide most of water in
rural areas. Surface water should not be use for drinking unless
treated. Water from wells is first filtered and it penetrates through the
layer of soil; this process removes suspended particles, including
microorganisms.
Water from home water supplies should be submitted for laboratory
examination periodically to assurance of potability.

The principle method used in treatment of Municipal water plant to
produce Potable water is Sedimentation, Filtration and Chlorination.
 Sedimentation occurs in large reservoir where water remains for a holding
period ; large particles settle in bottom. Sedimentation is enhanced by adding
Alum which produces a sticky, fluffy precipitate at surface.
• Many microbes and suspended particles are removes ad these precipitates
descend through water into settling a process which removes 99% of microbes.
Filtration Then water pass through large sand filter beds for further removal
of particulate matter.
Chlorination Subsequently, the water is chlorinated to kill any remaining
microbe and to assure it’s potability. The chlorine dosage must be sufficient to
leave a 0.2mg or 1.0mg of free chlorine per liter of water.
The purification process may include additional procedures like
removing minerals that make it hard, removing color ,balancing pH and
adding fluoride to avoid dental problems .
Municipal water Supplies:

Microbiology of domestic and sewage water

Micro-organisms as Indicator of water Quality
The routine microbial exam of water to determine it’s portability is not and should not
be based on its isolation and identification of pathogenic microbes on bases of
following reasons.
1. Pathogens are likely to enter water supply sporadically, and since they may not
survive for long periods of time, they could be missed from sample submitted to
laboratory.
2. If they are in small number, pathogens are likely to be escape detection in
laboratory.
3. 24hrs are needed to complete a report of water sample and within this time many
people could have use that water and have consumed that water and would have
exposed to the pathogens present in it before an action could be taken.
4. For these reasons, microbiologists have discovered such methods that are based
on finding a microbe whose presence indicates possibility of presence of
pathogenic microbes. The indicator microbes serve as ALARM.
Indicator Micro-organisms:
A kind of microorganism whose presence in water indicate the fecal contamination in
water from humans or any other warm blooded animal. This type of contamination
indicates that a pathogen occur in intestinal tract of animals are also present.

Some important characteristics of indicator
microbes:
1.Present in polluted water.
2.Quantity co-relates with amount of pollutant.
3.Survives better and longer than pollutants.
4.Has uniform and stable properties.
5.Generally harmless to humans and other
organisms.
6.Present in greater number than pollutants.
7.Easy to detect by standard laboratory
methods.

Escherichia coli most commonly
satisfies the requirements of an ideal
indicator of pathogens and is use in US
laboratories.
Other bacteria for pollution indicator are:
Streptococcus faecalis , Clostridium
perfringens both are inhabitants of Large
intestines of humans and other animals.
There is considerable interest for developing
methods to use virus for pollution indicator
but it requires more efficient methods than
bacteria as indicator.

Escherchia coli and other coliform bacteria:
E.Coli are
gram-negative
 spore forming
 rod shaped bacteria
 facultative
 ferments lactose with production of acid and gas within
48hrs at 35 Centigrade.
Lives in human intestine
And regarded as fecal type of coliform bacteria. Other
microbes of coliform group, Enterobacter aerogenes , are
widely distributed and found in soil, water, grain and also in
Human Intestine and regarded as non fecal. These species
are closely related and therefore, need Biochemical tests to
be differentiated :

1)Ability to produce Indole from tryptophan. E.coli
does produce and Ent. aerogenes does not.
2)Amount of acidity produced in glucose broth
medium and detected by pH indicator methyl red.
Both species produce but E.coli produces more
acid.
3)Ability to produce compound actylymethly-carbinol
in a glucose peptone medium. This chemical is
detected by Voges-Proskauer test procedure. E.coli
produces it the other does not.
4)Utilization of Sodium citrate. Ent. aerogenes is
capable of utilizing Sodium citrate as it’s the carbon
source for it but E.coli does not absorb it.

For convenience these test are designated as the IMViC reactions (I =
Indole, M= methyl red, Vi= Voges – Proskauer, and C = Sodium citrate).
Lactose Test:
Coliforms have several characters in common with species of genera
Salmonella and shigella which are pathogens. Major difference
between these and coliform is that coliform ferment lactose and they
don’t. So , Lactose fermentation is key test to detect Potability of
water.
Bacteriological Examination of
Water for Potability :
Method of examining water bacteriologically are contained in
the book Standard Methods for Examination of Water and
Waste Water and also in U.S. Environmental Protection
Agency.

The methods are standard and procedures must be
followed precisely if the results of the test are to have
official significance . It is essential that strict attention
be given to the following details when water samples are
submitted to Bacteriological analysis :
1) Sample must be collected in sterile container.
2) Sample must be representative of supply where it has
been taken from.
3) Contamination must be avoided during sample taking.
4) Sample should tested as promptly as possible.
5) If there is delay in examining then sample should be
stored at 0 to 10 degree Centigrade.
The routine bacteriological procedures consist of
1) Standard plate Count to determine number of bacteria
2) Test to reveal presence or absence of Coliform bacteria

Standard Plate Count test
Usually 1 to 0.1 ml water sample are plated on agar
and incubated for 24hr, after which colonies are
counted. When using this method to test water, there
are no particular number of bacteria that are
officially acceptable. This is because water with low
pathogens is more dangerous then with many
nonpathogenic bacteria. Nevertheless, water of good
quality has low bacterial count, fewer than 100 per
ml. This method is also useful in determining the
efficiency of various procedures for removing or
destroying organisms. It can perform before and also
after using any method to treat polluted water.

Membrane Filter Technique for
Water Analysis
The membrane filter technique for biological examination of water has following
steps:
1) A sterile filter disk is placed in filtration unit.
2) A measured amount of water flows through disk leaving bacteria on surface of
membrane filter disk.
3) Disk then removed and placed on an absorbent pad which was already soaked in
culture media. Special petri dishes that will hold the absorbent pad and membrane
are used for incubation.
4) During incubation colonies develop on filter disk wherever bacteria was
entrapped.
Advantages of this Technique:
 Large amount of water sample examined
 All microbes from sample retained on disk
 Results could be obtained rapidly

Nuisance Bacteria in Water System :
Certain bacteria are considered Nuisance Bacteria in water system
because it cause changes in odor, color and taste. Some form
precipitates of insoluble compounds in pipelines that reduce rate of
water flow. Algae may also cause change in odor , color and taste and
other objectionable characteristics. The following examples of these
bacteria cause undesirable changes:
1- Slime forming Bacteria: Produce gummy slimy secretions.
2-Iron Bacteria: Change soluble iron compounds into un soluble iron that reduce
water speed in pipelines.
3- Sulfur bacteria : Produce Sulfuric acid and Hydrogen sulfide which can make
water very acidic and make obnoxious odor.
4-Algae: Produce turbidity, color ,unpleasant odor and taste.

Swimming Pools:
Water in swimming places, particularly in public swimming
pools , may be health Hazard. Swimming pools and
surrounded area may transmit infection of eyes, nose,
throat, intestinal tract, also athlete foot and other
infections. Thus it is imperative that strict attention be
given to sanitary quality of water. There must be
surveillance of disinfection process to ensure that the
proper level of disinfection is maintained. Chlorine is used
widely as a disinfectant for swimming pool water.

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Sewage and waste water
treatment
 It is a mixture of domestic and industrial wastes.
 It is more than 99% water, but the remainder contains some ions,
suspended solids and harmful bacteria that must be removed before
the water is released into the sea.
 Sewage is a major carrier of disease (from human wastes) and toxins
(from industrial wastes).
 Industrial wastewater consist of acids, oil, greases, and animal and
vegetable matter discharged by factories.

Characteristics Of Waste Water
Physical And Chemical Characteristics of
wastewater
Microbiological characters

Physical And Chemical Characteristics of
wastewater
Domestic wastewater or sewage consists of:
 approximately 99.9% water,
 0.02 to 0.03% suspended solids,
 and other soluble organic and inorganic substances.
Organic and inorganic compounds are added by industrial wastes.
For example sugar factories, paper mills etc.
The organic compounds in sewage are classified as
nitrogenous(urea, proteins, and amino acids) and non
nitrogenous(carbohydrates, fates, and soaps).

Domestic wastewater or sewage contains human waste like feces,
urine, and gray water.
Gray water results from washing, bathing and meal preparations
Microbiological characters
Fungi, protozoa, bacteria, viruses and algae are present in wastewater
Untreated wastewater can contain millions of bacteria per milliliter of water
It includes coliforms,
Streptococci
Anaerobic spore forming bacilli
Proteus group
Etc.
Further microbes are added into wastewater from ground, surfaces, or
atmosphere

The need for wastewater treatment plants
 Goal of wastewater treatment:
 Protect health
 Preserve natural resources
 Prevent ecological damage
 Eliminate potential pathogens and toxins
 Decrease nutrient content (reduce microbial growth)
 Reduce B.O.D.
Biochemical oxygen demand (BOD):
Amount of oxygen required for microbial
decomposition of organic matter in sample

The treatment of wastewater is divided into
following phases:
 primary treatment
 secondary treatment
 Tertiary treatment
 How to accomplishes these goals:
 Use wastewater treatment plants(WWTP)
 The WWTP removes energy-rich organic matter before
discharge into the environment.
 And uses technology to prevent/lower the occurrence of water
borne diseases.

 secondary or biological treatment
 1) Activated sludge
 Atmospheric air or pure oxygen is introduced to a mixture of
primary treated or screened sewage (or industrial
wastewater) combined with organisms to develop a biological
floc which reduces the organic content of the sewage.

2) trickling filters
Trickling filter is a bed of crushed rocks—the 1ºtreated sewage
is trickled over it.
Lots of surfaces are present for microorganisms to attach..
3) Lagoons-
shallow ponds where algae like chlorella is present that consumes the nutrients
from wastewater.
4) Artificial wetlands
• Similar to lagoons
• Aerobic & anaerobic
environments
• Involves bacteria,
algae, plants,
sedimentation

Tertiary treatment
 Chemical flocculation  remove much of the remaining particulate
matter
Removal of phosphate and nitrates
 Disinfection
Performed before effluent is discharged
• Chlorine
• Ultraviolet light
So untreated water is treated now
After this the treated wastewater is discharge into sea.

Purification of Domestic water
• Purification of water involves physical, biological and chemical
processes such as:-
1. Filtration
2. Sedimentation
3. sand filters
4. Activated Sludge
5. Flocculation
6. Chlorination

Physical processes
1. Filtration is a mechanical or physical
operation which is used for the separation of
solids from fluids (liquids or gases) by passing
from a medium through which only the fluid
can pass.
•2.Sedimentation
• Sedimentation is the tendency for particles in
suspension or molecules in solution to settle
down in the fluid come to rest against a wall.

•Biological processes
Slow sand filters are used in water purification
for treating raw water to produce a potable
product. They are typically 1 to 2 metres
deep, can be rectangular or cylindrical in cross
section and are used primarily to treat surface
water.
4.Activated sludge
Atmospheric air or pure oxygen is introduced to
a mixture of primary treated or screened
sewage (or industrial wastewater) combined
with organisms to develop a biological floc
which reduces the organic content of the
sewage.

6.Chlorination
• Chlorination is the process of adding the element chlorine to water as a method
of water purification to make it fit for human consumption as drinking water.
Water which has been treated with chlorine is effective in preventing the spread
of water born disease.
Chemical process

Microbiology of domestic and sewage water

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