LECTURE
MICROBIOLOGY OF WATER AND WASTE WATER
Dr. Reeta Goel
Professor& Head
Department of Microbiology
College of Basic Sciences and Humanities
G.B. Pant Uni. of Agri. & Technology, Pantnagar
In urban areas, the household consumption of water is about 150 liters per
day per person. Water is used for bathing, washing utensils, washing clothes etc.
This domestic water consumption may vary with the lifestyle of community and
the availability of water. Most of the water taken into the house may be returned
as wastewater through drainage system. Moreover, industries also consume large
quantities of water and contribute to the discharged effluent.
WATER AND HEALTH
Water which is fit for human consumption is called drinking water or
potable water. Sometimes the term safe water is applied to potable water of a
lower quality threshold (i.e., it is used effectively for nutrition in humans that have
weak access to water cleaning processes, and does more good than
harm).Sometimes microorganisms that cause health problems can be found in
drinking water. However, as drinking water is thoroughly disinfected today,
disease caused by microorganisms is rarely caused by drinking water. There are
various bacteria and protozoa that can cause disease when they are present in
surface water (Table 1).
Water Purity Tests
•
Explain how water is tested for bacteriological quality
Historically, most of our concern about water purity has been related to the
transmission of diseases. Therefore, tests have been developed to determine the
safety of water; many of these tests are also applicable to foods.
It is not practical, however, to look only for pathogens in water supplies.
Because, if we were to find the pathogen causing typhoid or cholera in the water
system, the discovery would already be too late to prevent an outbreak of the
disease. Moreover, such pathogens would probably be present only in small numbers and might not be included in tested samples.
1
Table 1. various bacteria that can be found in surface water, and the
diseases caused by them .
Bacteria
Aeromonas
Campylobacter jejuni
Escherichia coli
Plesiomonas shigelloides
Salmonella
Streptococcus
Vibrio El Tor (freshwater)
Disease/ infection
Enteritis
Symptoms
Very thin, blood- and
mucus-containing
diarrhoea
Campilobacteriose
Flue, diarrhoea, headand stomachaches, fever,
cramps and nausea
Watery diarrhoea,
Urinary tract infections,
headaches, fever,
neonatal meningitis,
homiletic uraemia, kidney
intestinal disease
damage
Plesiomonas-infection
Nausea, stomachaches
and watery diarrhoea,
sometimes fevers,
headaches and vomiting
Typhoid fever
Fevers
Salmonellosis
Sickness, intestinal
cramps, vomiting,
diarrhoea and sometimes
light fevers
(Gastro) intestinal disease Stomachaches, diarrhoea
and fevers, sometimes
vomiting
(Light form of) Cholera
Heavy diarrhoea
The tests for water purity in use today are aimed for detection particular
indicator organisms. There are several criteria for an indicator organism, the
most important being that the microbe is consistently present in human feces in
substantial numbers so that its detection is a good indication that human wastes
are entering the water. The indicator organisms should also survive in the water at
least as well as the pathogens would. The indicator organisms must also be
detectable by simple tests that can be carried out by people with relatively little
training in microbiology.
Coliforms are defined as aerobic or facultatively anaerobic, gram-negative,
non-endospore-forming, rod-shaped bacteria that ferment lactose to form gas
within 48 hours of being placed in lactose broth at 35°C. Because some coliforms
are not solely enteric bacteria but are more commonly found in plant and soil
samples, many standards for food and water specify the identification of fecal
2
coliforms. The predominant fecal coliform is E. coli, which constitutes a large
proportion of the human intestinal population. There are specialized tests to
distinguish between fecal coliforms and nonfecal coliforms. Further, coliforms are
not themselves pathogenic under normal conditions, although certain strains can
cause diarrhea and opportunistic urinary tract infections.
The common methods for determining the presence of coliforms in water are
largely based on the lactose-fermenting ability of coliform bacteria. The multipletube method can be used to estimate coliform numbers by the most probable
number (MPN) method. The membrane filtration method is a more direct method
of determining the presence and numbers of coliforms.
A more convenient method of detecting coliforms, specifically the coliform E.
coli, makes use of media containing the two substrates o-nitrophenyl-β-Dgalactopyranoside (ONPG) and 4-methylumbelliferyl-β-D-glucuronide (MUG).
Coliforms produce the enzyme β-galactosidase, which acts on ONPG and forms a
yellow color, indicating their presence in the sample. E. coli is unique among
coliforms in almost always producing the enzyme β-glucurom'dase, which acts on
MUG to form a fluorescent compound that glows blue when illuminated by longwave ultraviolet light. These simple tests, or variants of them, can detect the
presence or absence of coliforms or E. coli and can be combined with the
multiple-tube method to enumerate them. It can also be applied to solid media,
such as in the membrane filtration method. The colonies fluoresce under UV light.
Coliforms have been very useful as indicator organisms in water sanitation, but
they have limitations. One problem is the growth of coliform bacteria embedded in
layers of biological slime (or biofilms, discussed in detail shortly) on the inner
surfaces of water pipes. These coliforms do not, then, represent external fecal
contamination of the water, and they are not considered a threat to public health.
Wastewater
Wastewater is liquid effluent derived from domestic sewage of industrial
sources that cannot be discarded in untreated form into lakes or streams due to
public health, economic and aesthetic considerations. Sewage is liquid effluent
contaminated with human or animal fecal materials. For technical purpose can be
divided into urban and industrial wastewater. The composition of the former
usually conforms to a general typology.
3
Most industrial processes emit wastewater during one or more stages of
production. The composition of this type of water can vary dramatically as it is
determined both by the products themselves and processes of production. All
these waste waters contain organic and inorganic wastes as suspended or
dissolved matter. In addition they may also contain microorganisms, including
those of faecal origin and pathogenic nature.
The solids content of an urban wastewater may be physically classified
approximately as shown in fig. 1 (Metcalf and Eddy, 1987)
Fig.1 Classification of solids found in urban wastewater (Metcalf and Eddy, 1987)
In a typical urban wastewater, about 75 percent of the suspended solids
and more than 50 percent of the filterable solids are organic in nature. These
solids are derived from both the animal and plant kingdoms and the activities of
these as related to the synthesis of organic compounds. The principal groups of
organic substances found in wastewater are proteins (40 to 60 %), carbohydrates
(25 to 50 %), fats and oils(10 % (Metcalf and Eddy, 1987). Beyond these
substances, wastewater contains small quantities of a large number of different
synthetic organic molecules. Surfactants, phenols and pesticides are typical
compounds.
4
Various forms of nitrogen in urban wastewater (Ekama et al., 1984)
Industrial waste generally has a strong odour. The substances responsible
for causing odour and taste are phenol compounds, sulphur compounds, iron,
manganese, sodium chloride, calcium chloride, magnesium salts, acids,
hydrocarbons, often present in wastes from gas and wood industries, refineries
and various chemical industries (Mendia, 1962).
Microbiological Characteristics of Sewage
The sewage composition varies depending upon the source of wastewater.
This also causes variation in the microbial flora of sewage. Almost all groups of
microorganisms, algae, fungi, protozoa, bacteria and viruses are present. The
bacterial group comprises mainly the soil borne organisms, Bacillus subtilis, B.
megaterium, B. mycoides, Pseudomonas fluorescens, Achromobacter spp. and
Micrococcus spp. Bacteria of intestinal origin also occur in sewage in large
numbers. Mostly these are pathogens. Examples of this type are Escherichia coli,
and other coliforms, Proteus and Serratia species. Potential pathogens include
enterococci (Streptococcus faecalis) and Clostridium perfringens. Pathogenic
bacteria which cause serious illness like Vibrio cholerae, Salmonella typhi, S.
paratyphi and Shigella dysenteriae may also occur in sewage. Viruses (released
in the faeces from infected host) are also occasionally found in sewage, for
example, poliomyelitis virus, infectious hepatitis virus and Coxsackie’s virus.
Bacteriophages also occur in comparatively large numbers. During treatment
process the microbial flora may be dominated by the corresponding physiological
groups.
5
WASTEWATER AND SEWAGE TREATMENT
Wastewater treatment refers to the process of removing pollutants from water
previously employed for industrial, agricultural, or municipal uses. The main
objectives of the sewage treatment are:
•
To convert waste and wastewater into a readily reusable resource.
•
To prevent pollution of any water body to which treated or reused water
enters.
•
To reduce the BOD (biochemical oxygen demand) of sewage from 30 mg/l
to about 20 mg/l in the final effluent.
•
To destroy the causative agents of waterborne diseases
Wastewater
and
sewage
treatment
involves
a
large-scale
use
of
microorganisms and can be considered a type of industrial-scale bioconversion.
Wastewater enters a treatment plant and, following treatment, the effluent water is
suitable for release into rivers and streams or to drinking water purification
facilities. The techniques used to remove the pollutants present in wastewater can
be broken into biological, chemical, physical, and energetic. These different
techniques are applied through the many stages of wastewater treatment.
Systems commonly used for treatment of urban wastewater are constituted of
primary treatment by settling, a biological second stage, and a tertiary treatment
by disinfection, in some cases following a filtration process.
Primary sedimentation is most efficient in removing coarse solids.
Biological processes are used to convert the finely dissolved organic matter in
wastewater into flocculant settleable solids that can be removed in sedimentation
tanks. These processes are employed in conjuction with physical and chemical
processes and they are most efficient in removing organic sub-stances that are
either soluble or in the colloidal size range. Disinfection is generally operated by
chlorination with Cl2 or NaOCl.
The main systems for removal of solids, organic matter and pathogens are
the activated sludge process, trickling filters, aerated lagoons, high-rate oxidation
ponds, stabilization ponds. Stabilization ponds or aerated lagoons are most often
used for small installations. The activated sludge process, or one of its many
6
modifications, is most often used for larger installations. In some cases trickling
filters are applied.
Several processes have been used for activated sludge. The most
important are (Metcalf and Eddy, 1987): tapered aeration process; modified
aeration process; continuous-flow stirred tank; step aeration process; contact
stabilization process; extended aeration process; oxidation ditch; carrousel
system; high-rate aeration process.
Wastewater treatment and biochemical oxygen demand
The goal of a wastewater treatment facility is to reduce organic and
inorganic materials in wastewater to a level that no longer supports microbial
growth and to eliminate other potentially toxic materials. The efficiency of
treatment is expressed in terms of a reduction in the biochemical oxygen demand
(BOD), the relative amount of dissolved oxygen consumed by microorganisms to
completely oxidize all organic and inorganic matter in a water sample. Higher
levels of utilizable organic and inorganic materials in the wastewater result in a
higher BOD. Typical values for domestic wastewater, including sewage are
approximately 200 BOD units. For industrial wastewater for example from sources
such as dairy plants, the values can be as high as 1500 BOD units. An efficient
wastewater treatment facility reduces levels to less than 5 BOD units in the water
released from the treatment plant.
A typical wastewater facility must treat both sewage and industrial wastes.
Treatment is a multistep operation employing a number of independent physical
and biological process. Primary, secondary(Fig.3) and sometimes tertiary
treatments are employed to reduce fecal and chemical contamination in the
incoming water. Each level of treatment employs more complex and more
expensive technologies.
Primary treatment
Primary treatment usually includes the removal of large solids from the
wastewater via physical settling or filtration. The first step in primary treatment is
screening. Wastewater entering the treatment plant is passed through a series of
grates and screens that remove large objects. The effluent is left to settle down for
a number of hours to allow suspended solids to sediment. Municipalities that
provide only primary treatment suffer from extremely polluted water when the
7
effluent is discharged into adjacent waterways because high levels of organic
matter and other nutrients remain in water following primary treatment. Therefore,
most treatment plants employ secondary treatment to reduce the organic content
of the wastewater before release to natural waterways. Secondary treatment is
intimately tied to microbiological processes.
Secondary Treatment
Secondary treatment typically removes the smaller solids and particles remaining
in the wastewater through fine filtration aided by the use of membranes or through
the use of microbes, which utilize organics as an energy source. Energetic
techniques may also be employed in tandem with biological techniques in the
secondary phase to break up the size of particles thus increasing their surface
area and rate of consumption by the microbes present. A common first step in the
secondary treatment process is to send the waste to an aeration tank.
Anoxic secondary wastewater treatment
Anoxic wastewater treatment involves a series of digestive and fermentative
reactions carried out by a number of bacterial species and is usually employed to
treat materials that have large amounts of insoluble organic matter (and hence
very high BOD), such as fiber and cellulose waste from food-and dairy processing
plants. The anoxic degradation process itself is carried out in large enclosed tanks
called sludge digesters or bioreactors
and requires the collective activities of
many different types of microorganisms.Through the action of the resident anoxic
microorganisms, the macromoleculare waste components are first digested by
polysaccharases, proteases and lipases into soluble components. These soluble
components are then fermented to yield a mixture of fatty acids, H2 and CO2 and
the fatty acids are further fermented to acetate, CO2 and H2. These products are
then used as substrates by methanogenic bacteria, which are capable of carrying
out the reactions CH3COOH
CH4+CO2 and 4H2O + CO2
CH4 + 2H2O. Thus
major products of anoxic sewage treatment are CH4 (methane) and CO2. The
methane can be collected and either burned off or used as fuel to heat and power
the treatment plant.
Aerobic secondary treatment
In general, nonindustrial wastewater can be treated efficiently using only aerobic
secondary treatment. Several kinds of aerobic decomposition processes are used
8
for wastewater treatment, but the trickling filter and activated sludge methods
(Fig.2) are the most common. A trickling filter is a bed of crushed rocks, about 2 m
thick, on tip of which the wastewater is sprayed. The liquid slowly passes through
the bed, the organic matter adsorbs to the rocks and microbial growth occurs on
the rocks. The complete mineralization of organic matter to carbon dioxide,
ammonia, nitrate, sulfate and phosphate takes place in the microbial biofilms on
the rocks. The most common aerobic treatment systems is the activated sludge
process. Here, the wastewater to be treated is mixed and aerated in a large tank.
Slime-forming bacteria, including Zooglea ramigera, among others, grow and form
flocs (large, aggregated masses) and these flocs form the substratum to which
protozoa and small animals attach. Occasionally, filamentous bacteria and fungi is
pumped into a holding tank or clarifier where the flocs settle. Some of the floc
material (called activated sludge) is then returned to the aerator to serve as
inoculum and the rest is sent to the anoxic sludge digestor or is removed, dried
and burned or used for fertilizer.
Fig.2; Simple Activated Sludge with Trickling filter
Wastewater normally stays in an activated sludge tank for 5 to 10h, a time
too short for complete oxidation of all organic matter. However, during this time
much of the soluble organic matter is adsorbed to the floc and is incorporated into
microbial cells. The BOD of the liquid effluent is considerably reduced (by up to
95%) by this process, with most of the BOD now contained in the settled flocs and
the goal of BOD reduction in the water is achieved. Nearly complete BOD
reduction can occur if the flocs are then transferred to the anoxic sludge digestor.
9
Most treatment plants now chlorinate the effluent (to further reduce the possibility
of biological contamination) and discharge the treated water to streams or lakes. A
few plants, however, process wastewater through a tertiary stage.
Tertiary treatment
Tertiary treatment is the most complete method of treating sewage but has not
been widely adopted because it is very expensive. Tertiary treatment is a
physicochemical process employing precipitation, filtration and chlorination
procedures similar to those employed for drinking water purification to sharply
reduce the levels of inorganic nutrients, especially phosphate and nitrate, from the
final effluent.
Fig.3: Primary and secondary treatment of raw water
Physiochemical purification
A typical drinking water treatment installation for a small city is shown in
figure 4. Raw water is first pumped from the source, in this case a lake, to a
sedimentation basin where anionic polymers, alum (aluminum sulfate), and
chlorine are added. Sand, gravel and other large particles settle out. This
pretreated water is then pumped to a clarifier or coagulation basin, a large holding
tank where coagulation takes place. The alum and anionic polymers form larger
suspended particles from the much smaller suspended colloidal particles. After
mixing, the particles continue to interact, forming large, aggregated masses, a
10
process known as flocculation. The large, aggregated particles, called floc, settle
out by gravity, trapping any remaining microorganisms and absorbing organic
matter and sediment. After coagulation and flocculation, the clarified water
undergoes filtration. The water is passed through a series of filters designed to
remove the remaining suspended particles and microorganisms. The filters
usually consist of thick layers of sand and ionic filtration media. When combined
with previous purification steps, the filtered water is free of all particulate matter,
most organic and inorganic chemicals, and all microorganisms.
Disinfection
Clarified, filtered water must then be disinfected before it is released to the supply
system as pure, potable finished water. Chlorination is the most common method
of disinfection. In sufficient doses, chlorine kills microorganism within 30 minutes
(certain pathogenic protozoa such as Cryptosporidium are not easily killed by
chlorine treatment and thus can be important waterborne pathogens. In addition to
killing microorganisms, chlorine reacts with organic compounds, oxidizing and
effectively neutralizing them. Therefore, since most taste and odor-producing
compounds are organic in nature, chlorine treatment also improves water taste
and smell. Chlorine is added to water either from a concentrated solution of
sodium or calcium hypochlorite or as a gas from pressurized tanks. The latter
method is used most commonly in large water treatment plants because it is most
amenable to automatic control.
11
Fig. 4: Water treatment system
Further Reading
Ekama G.A., G.v.R. Marais and I.P. Siebritz., (1984). Biological Excess
Phosphorus Removal. In Theory, Design and Operation of Nutrient
Removal Activated Sludge Processes, information document prepared for
the Water Research Commission by the University of Cape Town, City of
Council of Johannesburg and the National Institute for Water Research of
the CSIR, Pretoria.
Mendia L., (1962). Aspetti tecnici del problema degli scarichi industriali.
Ingegneria
Sanitaria, N. 1.
Metcalf and Eddy, Inc., (1987). Wastewater Engineering: Treatment, Disposal,
Reuse. Tata McGraw-Hill Publishing Company Ltd., New Delhi, second
edition, 6th reprint.
12
*Basic Terminology of Microbiology
Autoclave
:
Bacteria
:
Biofilms
;
Bioremediation
:
Biotechnology
:
Coccus
Coliforms
:
:
Colonization
:
Colony
:
Complex media
:
Consortium
:
Culture
:
Culture medium
:
Disease
Eukarya
:
:
Extremophile
:
Fungi
:
Gene
:
Gram-negative cell
:
Gram-positive cell
:
A sterilizer that destroys microorganisms by high
temperature using steam under pressure
All prokaryotes that are not members of the
domain Archaea
Microbial colonies encased in an adhesive,
usually polysaccharide material, and attached to
a surface
Use of microorganisms to remove or detoxify
toxic of unwanted chemicals in an environment
The use of living organisms to carry out defined
chemical processes for industrial application
a spherical bacterium
Gram-negative, nonsporing, facultative rods that
ferment lactose with gas formation within 48 hr at
35o C
Multiplication of a microorganism after it has
attached to host tissues or other surfaces
A macroscopically visible population of cells
growing on host tissues or other surfaces
Culture
media
whose
precise
chemical
composition is unknown. Also called underfined
media
A two-(or more) membered bacterial culture (or
natural assemblage) in which each organism
benefits from the others
A particular strain or kind of organism growing in
a laboratory medium
An aqueous solution of various nutrients suitable
for the growth of microorganisms
Injury to the host that impairs host function
The Phylogenetic domain containing all
eukaryotic organism
An organism that grows optimally under one or
more chemical or physical extremes, such as
high or low temperature or pH
Nonphototrophic eukaryotic microorganisms that
contain rigid cell walls
A unit of heredity; a segment of DNA specifying a
particular protein or polypeptide chain, a tRNA or
an rRNA
A prokaryotic cell whose cell wall contains
relatively little petidoglycan but has an outer
membrane composed of lipopolysaccharides,
lipoprotein and other complex macromolecules
A prokaryotic cell whose cell wall contains
relatively little peptidoglycan and lacks the outer
membrane or gram-negative cells
13
Growth
Growth rate
:
:
Guild
Microorganisms
:
:
Nutrient
:
Parasite
:
Pasteurization
:
Pathogen
:
Pure culture
:
Stationary phase
:
Sterilization
:
Strain
:
Virus
:
Water activity (aw)
:
Xenobiotic
:
Yeasts
:
In microbiology, an increase in cell number
The rate at which growth occurs, usually
expressed as the generation time
A group of metabolically related organisms
A microscopic organism consisting of a single cell
or cell cluster, also including the viruses
A substance taken by a cell from its environment
and used in catabolic or anabolic reactions
An organism able to live on and cause damage to
another organism
Destruction, usually by heat treatment, of all
diseases-producing, microorganisms along with a
reduction
in
the
number
of
spoilage
microorganism
An organism able to inflict damage on a host it
infects
A culture containing a single kind of
microorganism
The period during the growth cycle of a microbial
population in which growth ceases
The killing or removal of all living organism and
their viruses from a growth medium
A population of cell of a single species all
descended from a single cell; a clone
A genetic element containing either DNA or RNA
that replicates in cells but is characterized by
haing an extracellular state
An expression of the relative availability of water
in a substance. Pure water has an aw of 1.000
A completely synthetic chemical compound not
naturally occurring on Earth
Unicellular fungi
* Source: Brock Biology of Microorganism 2003, 10th Edition
14
Water Purification and Public Health
S.P. Singh
Prof. & Head
Department of Veterinary Public Health
College of Veterinary and Animal Sciences,
G. B. Pant University of Agri. & Tech., Pantnagar-263145
Water and Health
The world’s population is expected to increase every year by 74.8 million.
To meet requirement of water for such a huge population, sincere efforts are
being made at international level. The United Nations have declared “2005-2015”
as the International Decade for “Water for life” and World agenda has been set
focusing the water related issues. This issue is of great consequence since
approximately 1.8 million people die every year from diarrhoeal diseases
(including cholera); mostly in developing countries where 88% of diarrhoeal
disease is attributed to unsafe water supply, inadequate sanitation and hygiene.
Improvements in drinking-water quality through household water treatment, such
as chlorination at point of use can lead to a significant reduction of diarrheal
episodes. There is a need to undertake an integrated water resources
management so as to provide safe and clean water to all.
Waterborne diseases occur not only as an endemic but also often appear
as an epidemic. In the context of zoonoses, the waterborne diseases have
significance in both developed as well as developing countries alike. The
associated pathogens are transmitted predominantly by faecal-oral and
occasionally by faecal-droplet routes.
Consequent to the dynamics in the population as well as its resultant effect
on the environment, many pathogens are taking newer and virulent forms
resulting in the emergence and re-emergence of the waterborne disease. Such
changes are not free from the adverse consequences on the public health and
these
include
(i)
changing
patterns
of
water
use
(ii)
population
growth/migration/variation (iii) increased population of the immunocompromised
(consequent to the malnourishment as well as immunodeficiency diseases such
15
as AIDS and its deadly combinations with tuberculosis/toxoplasmosis etc) (iv)
increased use of water due to the changed lifestyle and access to recreational
activities (v) water scarcity, climate changes, disasters, & the emergencies (vi)
war and bioterrorism (vii) increased population in the urban and periurban areas
(viii) use of non-conventional alternatives to meet the never ending human
demands (ix) increased use of agro-chemicals, antibiotics, growth promoters, and
other veterinary drugs for the production and protection of plants, animals and
human (x) altered ecological rhythm and (xi) the global trade, its regulations and
their related consequences.
Zoonotic pathogens have been encountered in water as a cause of gastroenteric infections with the symptoms of diarrhea in many countries. But, still there
exist many diseases that just escape the diagnosis process. Leptospirosis, E. coli
O157:H7, Cryptosporidiosis, Campylobacter, Toxoplasmosis and Giardiasis, occur
regularly in some countries. It is also important to mention more than 75% of all
the emerging pathogens are zoonotic on nature. Further, animals and other lower
vertebrate or non-vertebrates play an equal role as that of human in the
maintenance or transmission of such infections that ultimately threaten the human
life by the way of vehicles, particularly water.
A variety of bacteria, parasites, fungi, viruses can be acquired by the way
of water. The transmission routes involve drinking, contact, water use (food
preparation, agriculture) exposure to wastewater, faeces, urine, and abattoir
waste.
The viruses / prion particles possess considerable host specificity yet can
infect the related species. There are 1.5 million cases of clinical hepatitis reported
every year.Many of the bacterial pathogens are well established water borne
pathogens such as Salmonella, E. coli O157:H7, Campylobacter, Yersinia,
Mycobacterium avium (ssp. paratuberculosis) and Leptospira. They can be
transmitted by improperly purified water and can put the end users of water at risk.
The waterborne zoonotic bacteria are principally those shed in faeces by warmblooded animals (birds and mammals), although some are also harbored by
reptiles.
16
Although fungi are transmitted directly by contact but at times, water can
act an agent of transmission and the infections such as Trichophyton spp.,
Cryptococcus, and Coccid odes may enter by such route.
Protozoan pathogens originating from animal and human waste have been
recorded from water sources throughout the world. A number of well documented
waterborne
zoonotic
protozoa
exist,
including
Giardia
intestinalis,
Cryptosporidium, Toxoplasma gondii, and Entamoeba histolytica. There are other
potential candidates including Cyclospora, where waterborne transmission has
been demonstrated but a zoonotic route remains to be established. Protozoan
pathogens,
including
microsporidia,
amoebae,
ciliates,
flagellates,
and
apicomplexans, originating in human or animal faeces have been found in surface
waters worldwide The zoonotic protozoa that are emerging or are of renewed
interest consequent to their spread associated with water include several species
of microsporidia, the amoeba Entamoeba histolytica, Giardia duodenalis (G.
lamblia), Toxoplasma gondii, and Cryptosporidium spp. Although Cyclospora
cayetanensis is known to be a waterborne threat and has been detected in
washings from vegetables contaminated with irrigation water, humans are the only
confirmed hosts for this species.
Major helminthic zoonoses include nematodes such as ascarids, pinworms,
hookworms, strongylids, angiostrongylids, capillarids, and guinea worms, flukes
such as schistosomes and liver flukes, and tapeworms such as the beef, pork,
and fish tapeworms, as well as cystic and alveolar hydatid tapeworms. Poor
sanitation and poor water quality facilitate transmission among animals and
humans.
Water purification
The ultimate purpose of water purification is inactivation and removal of
pathogens such as bacteria, viruses, parasites, microbial toxins and other
miscellaneous pathogens, as well as elimination of contaminants that arise into it
by the way of its pollution at various levels of the distribution system. Hence
routine analysis of water is a mandate to assess the number of pathogens in the
water, to select a suitable treatment facility to assure the consumers about
wholesomeness of the water. Since decades, a composite system known as
“multiple barrier concept” have been in use for the purification of water, which
17
holds good till today. This includes protection of the source of water, coagulation,
flocculation, sedimentation, filtration, disinfection, and finally protection of the
water distribution systems. But the recent epidemiological data indicate lacunae in
such traditional systems and there is a need to modify them by adding ‘multistage
filtration and disinfection’ especially to remove the pathogens and still stringent
treatment so to remove the environmental pollutants, contaminants and other
miscellaneous substances that have health implications. There is a need to
implement HACCP in the water related industries so as to keep the contaminants
at the lowest possible limits. Water safety plan has also to set and followed strictly
as per the recommendations of the competent authorities. Frameworks need to be
strengthened to so as to maintain minimum residual concentrations of the
disinfectants in the distribution systems even taking care health implications
arising from such chemicals.
Keeping in view the public health significance of water, it must pass
through the various stages of water purification system. The various water
purification processes include are described as follows:
Boiling for one minute can kill harmful organisms and thus can be
considered as a reliable method. Various halogens such as iodine and chlorine
preparations can also serve the function. Iodination is a very effective and
convenient method for water purification as it destroys bacteria, viruses and
protozoan cysts in concentration temperature and duration dependent destruction
of such pathogens (8 mg/liter at 20 0C for 10 minutes). Preparations of iodine such
as tincture of iodine (4 drops in a 1 litre of water or one drop for a glass), iodine
crystals and tablets can be used for the purpose; but all the halogens are not
effective against Cryptosporidium. While using iodine preparations for water
purification, proper care must be taken for pregnant women, very young
individuals and the persons suffering from thyroid disease or iodine allergy. After
the iodine application, the taste due to remaining iodine residues can be
eliminated by the use of vit-C tablets, lime or lemon juice.
The various processes employed for removal of microbes from the water
include (i) pre-treatment by using any process that modifies microbial water quality
before, or at the entry to, a treatment plant; (ii) coagulation, flocculation and
sedimentation by which small particles interact to form larger particles and settle
18
out by gravity; (iii) ion exchange used for the removal of calcium, magnesium and
some radionuclide; (iv) Granular filtration, in which water passes through a bed of
granular materials after coagulation pretreatment; (v) slow sand filtration, in which
water is passed slowly through a sand filter by gravity, without the use of
coagulation pretreatment.
Pre-treatment
Pre-treatment of water (roughing filters, microstrainers, off-stream storage
and bank infiltration), help in the removal of algae, turbidity, viruses and protozoan
cysts. During pretreatment a variety of treatment s are undertaken that vary in
their complexity and may vary from disinfection to membrane filtration.
Roughing employed for pretreatment are filters derived from rock or gravel
that are used prior to filtration (slow sand) process to reduce turbidity (up to 6090%), coliform count (93-99.5%), algal cell (37%), total chlorophyll (53%). Further;
color, organic carbon, and the turbidity can still be reduced by the use of alum
coagulant.
Micro strainers are made of fabric meshes woven of stainless steel or
polyester wires and many large sized protozoa such as Balantidium coli, but
smaller pathogens such as bacteria or viruses can not be removed and these also
reduce turbidity (5–20%) which can even be enhanced by the use of coagulants
(alum).
The quality of water in the ‘off-stream storage’ reservoirs that feed the
potable water source directly or indirectly feeds a potable water intake is
determined by the physical, biological and chemical processes taking place in it.
The algal growth, influx of nitrogen, phosphorous and other contaminants and the
faecal contamination at or near surroundings should be limited even attempts
should be made to reduce birds. If properly stored at off-storage reservoirs there
can be significant reduction in the counts of Cryptosporidium, E.coli, Giardia, and
entero-viruses. Further, storage of water in divided reservoirs is better compared
to single large reservoir.
A process of surface water seeping from the bank or bed of a river or lake
to the reduction wells of a water treatment plant is known as ‘Bank infiltration’
which is used in some of the European countries. This process reduces Giardia,
19
Cryptosporidium, Clostridia, bacteriophase and certain viruses such as Entero and
Reoviruses.
Coagulation, flocculation and sedimentation
Coagulation, flocculation and sedimentation are used in conjunction with
subsequent filtration. Coagulation promotes the interaction of small particles to
form larger particles. In practice, the term refers to coagulant addition (i.e. addition
of a substance that will form the hydrolysis products that cause coagulation),
particle destabilization and inter-particle collisions. Flocculation is the physical
process of producing inter-particle contacts that lead to the formation of large
particles. Sedimentation is a solid–liquid separation process, in which particles
settle under the force of gravity. Most bacteria and protozoa can be considered as
particles, and most viruses as colloidal organic particles that are eliminated by
such processes.
Conventionally, clarification refers to chemical addition, rapid mixing,
flocculation and sedimentation. Here the chemical coagulation is critical for
effective removal of microbial pathogens, in the absence of a chemical coagulant;
removal of microbes is low because sedimentation velocities are low. When
properly performed, coagulation, flocculation and sedimentation can result
inconsiderable
removals
of
bacteria,
viruses
and
protozoa.
However,
Cryptosporidium and Giardia are found at very low levels, and methods for their
detection have limitations use of coagulants further helps in the reduction of
turbidity. Removal of bacteria (E. coli vegetative cells and Clostridium perfringens
spores) and protozoa (Giardia cysts and Cryptosporidium oocysts) is possible but
this can be achieved by the use of iron-based coagulants which are slightly more
efficient than alum (aluminum hydroxide) or poly-aluminum chloride (PACl);
however, coagulation conditions (i.e. dose, pH, temperature, alkalinity, turbidity
and the level and type of natural organic matter) affect the efficiency of removal.
‘High-rate clarification’ involves using smaller basins and higher surface
loading rates than conventional clarifiers, and is therefore referred to as high rate
clarification. Processes include ‘floc-blanket sedimentation’ (also known as ‘solidscontact clarification’), ‘ballasted-floc sedimentation’, and ‘adsorption or contact
clarification’. In floc-blanket sedimentation, a fluidized blanket increases the
particle concentration, thus increasing the rate of flocculation and sedimentation.
20
Ballasted-floc systems combine coagulation with sand, clay, magnetite or carbon
to increase the particle sedimentation rate. Adsorption or contact clarification
involves passing coagulated water through a bed where particles attach to
previously adsorbed material. Such processes help in the removal of algae,
Cryptosporidium and Giardia.
In ‘dissolved air flotation’ (DAF), bubbles are produced by reducing
pressure in a water stream saturated with air. The rising bubbles attach to flocparticles, causing the agglomerate to float to the surface, where the material is
skimmed off DAF can be particularly effective for removal of algal cells and
Cryptosporidium oocysts.
‘Precipitative lime softening’ is a process in which the pH of the water is
increased (usually through the addition of lime or soda ash) to precipitate high
concentrations of calcium and magnesium. Removal and reduction in the viability
of disinfection efficiency of Giardia, viruses and coliform bacteria is achieved.
‘In-line coagulation’ can be used with high-quality source waters (e.g. those
where turbidity and other contaminant levels are low). The coagulants are added
directly to the raw water pipeline before direct filtration.
‘Ion exchange’ is a treatment process in which a solid phase pre-saturant
ion is exchanged for an unwanted ion in the untreated water. The process is used
for water softening (removal of calcium and magnesium), removal of some radionuclides (e.g. radium and barium) and removal of various other contaminants (e.g.
nitrate, arsenate, chromate, selenate and dissolved organic carbon). The
effectiveness of the process depends on the background water quality, and the
levels of other competing ions and total dissolved solids.
Filtration using a wide variety of filters removes sand, clay and other matter
as well as organisms by means of small pore size membranes, adsorption,
exchange resins and osmosis. They effectively remove bacteria and parasites but
not viruses. Good filters are effective against Cryptosporidia and Giardia. Due to
the inability to remove viruses, filtered water must also be chemically treated or
boiled and hence many a times filtration is combined with other chemical
sterililants such as iodine (or chlorine) hence, modern filters incorporate chemical
disinfection, which is usually achieved by passing water through iodine exchange
resins. When negatively charged contaminants contact the iodine resin, iodine is
21
instantly released so killing the microorganisms without large quantities of iodine
being in solution.
Various filtration processes (diatomaceous earth; micro-filtration; nanofiltration; reverse osmosis; ultra-filtration) are used in drinking-water treatment.
Filtration can act as a consistent and effective barrier for microbial pathogens.
Granular high rate media filtration is the most widely used filtration process in
drinking water treatment. Under optimal conditions, a combination of coagulation,
flocculation, sedimentation and granular media filtration can result better removal
of protozoan pathogens with chlorine-resistant cysts.
The use of slow sand filtration to protect drinking-water consumers from
microbial risk was well established more than 100 years ago. Numerous disease
outbreaks due to chlorine-resistant protozoan pathogens in the past two decades
have increased interest in slow sand filtration because of its ability to remove
parasites. It can provide some degree of protection against microbial pathogens
reducing bacteria, protozoa (Cryptosporidium, Giardia) and turbidity.
‘Pre-coat filtration’ was developed by the US Army during World War II as a
portable unit for the removal of Entamoeba histolytica (a protozoan parasite
prevalent in the Pacific war zone) from drinking-water. The process involves
forcing water under pressure or by vacuum through a uniformly thin layer of
filtering material pre-coated onto a permeable, rigid, supporting structure (referred
to as a septum). Diatomite grades used for drinking-water treatment have a mean
pore diameter of 17 µm. Pre-coat filtration can remove protozoan parasites such
Giardia very effectively and the removal of Cryptosporidium can be significant, but
because organism is smaller than Giardia, it is more difficult to remove.
In membrane filtration, a thin semi-permeable film (membrane) is used as a
selective barrier to remove contaminants from water. There are very few
contaminants that cannot be removed by membrane processes. For the past two
decades, the use of membrane filtration in drinking-water treatment (including
pathogen removal) has been growing, due to increasingly stringent drinking-water
regulations and decreasing costs of purchasing and operating membrane filters.
The membrane processes most commonly used to remove microbes from
drinking-water are micro-filtration (pore size 0.1 µm or more), ultra-filtration ((pore
22
size 0.01 µm or more), nano-filtration (NF) and reverse osmosis (RO). Membrane
filtration eliminates most of bacteria, virus, protozoa and algae.
Bag, cartridge and fibrous filters are widely used in the recent past. A bag
filter is one that has a non-rigid fabric medium for the filter. Water flow is usually
pressure-driven from the inside of the filter bag to the outside. A cartridge filter is
one that has a rigid fabric medium or membrane for the filter. In this type of filter,
water flow is usually pressure-driven from the outside of the filter to the inside.
Bag and cartridge filters are often developed for small systems and for point-ofuse filtration applications. They are also sometimes applied as a pretreatment
process for membrane filtration. Bag filters and cartridge filters remove
microorganisms by physical straining. The removal efficiency thus depends
primarily on the pore size of the filter medium and on the size of the microbes. A
typical pore size range is from 0.2 to 10 µm. The pore size of the filter medium is
usually designed to be small enough to remove protozoa such as Cryptosporidium
and Giardia. Submicron particles, including viruses and most bacteria, can pass
through the filters. As water passes through a bag or cartridge filter, pressure drop
increases to a level impractical for operation. The bag or cartridge is then replaced
by a clean one. Since the removal mechanism is physical straining, chemical
pretreatment is usually not required for bag filters and cartridge filters. Straining of
large compressible particles can blind the filters and reduce filter life. High turbidity
and algae can also clog these filters. These processes are therefore only
appropriate for high-quality waters. A pre-filtration process may be employed to
remove large particles.
Disinfection of water and public health
Various disinfectants are used in the treatment of water used for drinking
purposes. Water treatment to inactivate pathogenic microbes: The disinfection
processes have strong bearing on the final quality of the water used for the
drinking purpose viz., (i) pre-treatment oxidation (wherein oxidants are added to
water early in the treatment process) (ii) primary disinfection which is a common
component of primary treatment of drinking-water, and important because
granular filter media do not remove all microbial pathogens from water and (iii)
secondary disinfection which is employed to maintain the water quality achieved
at the treatment plant throughout the distribution system up to the tap.
23
The factors like disinfectant concentration, contact time, temperature and
pH influence disinfection efficiency. Further, disinfection kinetics and CT of the
disinfectant (CT = concentration x contact time) have practical implications.
Increased resistance to disinfection may result from attachment or association of
microorganisms to various particulate surfaces, including, (i) macro-invertebrates
(Crustacea, Nematoda and Platyhelminthes); (ii) particles that cause turbidity; (iii)
algae; (iv) carbon fines and other miscellaneous substances.
Primary disinfection
A disinfection barrier is a common component of primary treatment of water
and is typically a chemical oxidation process, although ultraviolet (UV) irradiation
and membrane treatment are gaining increased attention. Different types of
disinfectant such as chlorine, monochlorine, chlorine dioxide, ozone, UV light and
mixed oxidants can be used various pathogenic microorganisms.
Chlorine and silver based preparations destroy most the bacteria (e.g.
V.cholerae), but are less effective against viruses (hepatitis A) and cysts (Giardia,
amoebic cysts, and Cryptosporidia). Chlorine alone is readily inactivated by
organic matter and its action varies with pH. However if used in combination with
Phosphoric acid it is more effective and this combination will destroy both Giardia
and Cryptosporidia.
Chlorine gas and water react to form HOCl and hydrochloric acid (HCl),
further HOCl dissociates into the hypochlorite ion (OCl–) and the hydrogen ion
(H+) which act as a germicide by destroying microorganisms by combining with
proteins to form N-chloro compounds and has effects on sulfhydryl groups and
convert them to several alpha amino acids by oxidation into a mixture of
corresponding nitriles and aldehydes. For nearly 100 years of chlorination of
drinking-water has demonstrated the effectiveness of this process for inactivation
of microbial pathogens, with the notable exception of Cryptosporidium. Even
certain bacteria show a high level of resistance to free chlorine. Spore forming
bacteria such as Bacillus or Clostridium are highly resistant when disseminated as
spores. Acid-fast and partially acid-fast bacteria such as Mycobacterium and
Nocardia can also be highly resistant to chlorine disinfection. Since Gram-positive
bacteria have thicker walls than Gram-negative ones the pathogenic group that
survives chlorination are gram positive as well as acid fast pathogens. Also,
24
enteric viruses are generally more resistant to free chlorine than enteric bacteria
due to the protective nature of the particle surface (Coxsackie A2). Protozoan
cysts such as Entamoeba histolytica and Giardia lamblia are highly resistant to
chlorine disinfection and may require prolonged contact times at high chlorine
residuals (2–3 mg/l) to achieve 99.9% acceptable inactivation and chlorine-based
disinfectants are generally not effective at inactivation of Cryptosporidium.
Monochloramine interact with nucleic acids or free purine and pyrimidine
bases by inducing single and double stranded breaks by transforming activity of
DNA and enhanced the sensitivity of DNA to endonuclease cleavage, it also
reacts to lesser extent with amino acids. Monochloramine is not recommended as
a primary disinfectant because of its weak disinfecting power also it is not effective
for inactivation of Cryptosporidium and hence in systems using monochloramine,
free chlorine is usually applied for a short time before addition of ammonia, or an
alternative primary disinfectant is used (e.g. ozone, chlorine dioxide). Treatment to
produce a monochloramine residual poses the risk of nitrite formation in the
distribution system, especially in low-flow stagnant areas, because bacteria on
surfaces and in deposits may nitrify any slight excess of ammonia.
Chlorine dioxide is a strong oxidant that can be used to control iron,
manganese and taste and odour causing compounds. It is highly soluble in water
(particularly at low temperatures), and is effective over a range of pH values (pH
5–10). Chlorine dioxide is thought to inactivate microorganisms through direct
oxidation of tyrosine, methionyl, or cysteine containing proteins, which interferes
with important structural regions of metabolic enzymes or membrane proteins. In
water treatment, chlorine dioxide has the advantage of being a strong disinfectant,
but not forming THMs or oxidizing bromide to bromate. Chlorine dioxide is roughly
comparable to free chlorine for inactivation of bacteria and viruses at neutral pH
but is more effective than free chlorine at pH 8.5. Chlorine dioxide is an effective
disinfectant for control of Giardia lamblia and Cryptosporidium. Chlorine dioxide
forms undesirable inorganic by-products (chlorite and chlorate ions) upon its
reaction with constituents of water such as dissolved organic carbon, microbes
and inorganic ions. Therefore, a water utility may need to provide additional
treatment depending on the level of these inorganic by-products and their specific
regulatory requirements.
25
Water can also be purified by the use of Ozone, which is very effective in
purifying water. Ozone use in water applications for treatment is now easier, more
efficient and much less costly. Ozone systems can be applied safely to any home
or business in water applications or effective air purification disinfectant. Ozone
has been used for more than a century for water treatment, mostly in Europe,
although its use is now spreading to okther countries. Ozone in aqueous solution
may react with microbes either by direct reaction with molecular ozone or by
indirect reaction with the radical species formed when ozone decomposes. Ozone
is known to attack unsaturated bonds, forming aldehydes, ketones or carbonyl
compounds. Additionally, ozone can participate in electrophilic reactions,
particularly with aromatic compounds, and in nucleophilic reactions with many of
the components of the microbial cell. Of the vegetative bacteria, Escherichia coli
are one of the most sensitive, while Gram-positive cocci (Staphylococcus and
Streptococcus), Gram-positive bacilli (Bacillus) and mycobacteria are the most
resistant. Mycobacterium avium can be effectively controlled by low doses of
ozone (CT=99.9 of 0.1–0.2 mg/min l–1), whereas the organism is highly resistant
to free chlorine (CT=99.9 of 551–1552 mg/min l–1 for water-grown isolates).
Viruses are generally more resistant to ozone than vegetative bacteria, although
phages appear to be more sensitive than human viruses. For the protozoa Giardia
lamblia and Naegleria gruberi, ozone inactivation did not follow linear kinetics, due
to an initial latent phase. Ozone is effective for removal of Cryptosporidium.
Ozonation is an effective process for destruction of both intracellular and
extracellular algal toxins. Essentially complete destruction of microcystins,
nodularin and anatoxin-a can be achieved if the ozone demand of the water is
satisfied.
UV light can be categorized as UV-A, UV-B, UV-C or vacuum-UV, with
wavelengths ranging from about 40 to 400 nm. The UV light in the UV-B and UVC ranges of the spectrum (200–310 nm) is effective for inactivating
microorganisms with maximum effectiveness at around 265 nm. Thymine bases
on DNA and ribonucleic acid (RNA) are particularly reactive to UV light and form
dimers (thymine–thymine double bonds) that inhibit transcription and replication of
nucleic acids, thus rendering the organism sterile. Thymine dimmers can be
repaired in a process termed ‘photo-reactivation’ in the presence of light, or ‘dark
26
repair’ in the absence of light. As a result, the strategy in UV disinfection has been
to provide a sufficiently high dosage to ensure that nucleic acid is damaged
beyond repair. Adenoviruses are double-stranded DNA viruses and are very
resistant to UV inactivation. Typical doses used for drinking-water disinfection
would not be effective for treatment of adenoviruses. Similarly, protozoa are also
sensitive to UV rays.
The use of mixtures of oxidants for microbial inactivation has gained
attention as a way to maximize the efficiency of current disinfectants. The
chemistry of mixed oxidant production is complex, resulting in a solution of free
chlorine, chlorine dioxide, ozone and various oxidation states of chlorine.
Secondary Disinfection
Secondary disinfection strategy is employed to maintain water quality in
distribution systems. The purpose of a secondary disinfectant is to maintain the
water quality achieved at the treatment plant throughout the distribution system up
to the tap. Secondary disinfection provides a final partial barrier against microbial
contamination and serves to control bacterial growth. The practice of residual
disinfection has become controversial, with some opponents arguing that if
biological stability is achieved and the system is well maintained, the disinfectant
is unnecessary.
Occasionally, corrosion of iron pipes can influence the effectiveness of
chlorine-based disinfectants for inactivation of biofilm bacteria. Microbial quality of
drinking-water cannot depend only on maintenance of a residual disinfectant. The
extensive nature of the distribution system, with many kilometres of pipe, storage
tanks, interconnections with industrial users and the potential for tampering and
vandalism, provides opportunities for contamination. Cross-connections are a
major risk to water quality. Although the risk can be reduced by vigilant control
programs, complete control is difficult to achieve and water utilities worldwide face
challenges in maintaining an effective cross-connection control program.
Backflow devices to prevent the entry of contaminated water are important as a
distribution system barrier. Because of high costs, backflow devices are installed
mainly on service lines for facilities that use potentially hazardous substances
(e.g. hospitals, mortuaries, dry cleaners and industrial users). Recent research is
focusing on transient pressure waves that can result in hydraulic surges in the
27
distribution system. These waves have both positive and negative amplitude,
meaning that they can create transient negative pressures (lasting only a few
seconds) in a distribution system, which may be missed by conventional pressure
monitoring. Because these waves travel through the distribution system, any point
where water is leaking out of the system is a potential entry point for microbes
during the brief period of negative pressure.
Conclusions
The water used for drinking purpose should not only be visibly clean but
also be wholesome and free from microbial as well as non-microbial
contaminants. The water purification is never an accident, stringent exercises
need to be undertaken so as to keep it away from these contaminants. Various
processes used for the purification of water suffer from one or the other lacunae,
thus, there is a need to use a composite system which can enhance safety. In the
industries, where water is used directly or indirectly for the preparation of food,
HACCP system needs to be implemented in order to reduce contamination of
water. The source of water should be kept clean and suitable primary purification
system should be employed as per the recommendations of the competent
authority. In situations, where the secondary disinfection is required, a strategy
needs to be first defined and then implemented to keep the pathogens away from
the water distribution system. Assurance for the supply of safe water to the
consumers should be the prime objective of public health administration in order
to safeguard the health of the public from the water associated problems.
28
WATER BORNE MICROBIAL DISEASES
V. D. P. RAO
Department of Veterinary Microbiology
College of Veterinary and Animal Sciences
G.B. Pant University of Agriculture & Technology,
Pantnagar – 263145
Water-borne diseases are infectious diseases spread primarily through
contaminated water. Many classes of pathogens excreted in the feces are able to
initiate waterborne infections. These are bacterial pathogens, including enteric
and aquatic bacteria, enteric viruses, and enteric protozoa. Though these
diseases are spread either directly or through flies or filth, water is the chief
medium for spread and hence they are termed as water-borne diseases.
Water borne microbial diseases are one of the major health hazards mainly
in the developing countries. Worldwide, in1995 contaminated water and food
caused death of more than three million persons of which more than 80% were
among children of 5 years of age (Mary and Ross, 1996). In India, more than 70%
of the epidemic emergencies are either water borne or water related.
Most intestinal (enteric) diseases are infectious and are transmitted through
faecal waste. Pathogens – which include virus, bacteria, protozoa, and parasitic
worms – are disease-producing agents found in the faeces of infected persons.
These diseases are more prevalent in areas with poor sanitary conditions. These
pathogens travel through water sources and interfuses directly through persons
handling food and water. Since these diseases are highly infectious, people
looking after an infected patient should maintain extreme care and hygiene.
Hepatitis, cholera, dysentery, and typhoid are the more common water-borne
diseases that affect large populations in the tropical regions.
Water borne bacterial diseases:
Clostridium: The bacteria are found in soil, fresh water or marine sediments. The
Genus Clostridium is having many species that are pathogenic in animals and
human
beings
that
can
be
classified
into
–
neurotoxic,
histotoxic,
enteropathogenic and enterotoxemia producing Clostridia.
29
Neurotoxic clostridia include C. tetani and C. botulinum. C. tetani causes tetanus
in animals and humans and leads to synaptic inhibition and muscular spasms. C.
botulinum inhibits neuromuscular transmission and leads to flaccid paralysis.
Histotoxic group of clostridia includes many species of genus Clostridium
causing variety of diseases in animals. C. chauvoie causes black leg in cattle and
sheep. C. septicum causes malignant oedema in cattle, pig and sheep and
abomasitis in sheep. C. novyi type A causes big head disease in young ram and
type B causes infectious necrotic hepatitis (black disease) in sheep and
occasionally in cattle. C. haemolyticum causes bacillary haemoglobiniuria in cattle
and sheep. C. perfringens type A causes necrotic enteritis in chicken and
necrotizing enterocolitis in pigs.
Enteropathogenic and enterotoxemia producing Clostridia: This group
includes type A to type E. Clostridium perfringens type A causes disease
conditions viz., necrotic enteritis in chicken, necrotizing enterocolitis in pigs and
canine haemorrhagic gastroenteritis. Type B causes lamb dysentery and
haemorrhagic enteritis in calves and foals. Type C causes struck in adult sheep,
necrotic enteritis in chickens and haemorrhagic enteritis in neonatal piglets. Type
D causes pulpy kidney in sheep, enterotoxaemia in calves, adult goats and kids.
Type E is responsible for haemorrhagic enteritis in calves and enteritis in rabbits
(Quinn et al. 2002).
Listeria: This bacterium can replicate in the environment and can be recovered
from herbage, faeces of animals, sewage effluents and bodies of fresh water. L
monocytogenes causes encephalitis, abortion, septicaemia or encephalomyelitis
mainly in case of sheep, goat and cattle but some times dog, cat, horse and pigs
may also get affected.
Mycobacteria: Lipid rich wall of mycobacteria is hydrophobic and resistant to
adverse environmental influences. The bacteria are found in soil, vegetation and
water and are obligate pathogens, shed by infected animal, can survive in
environment for long periods. The bacteria cause tuberculosis and J.D. in various
species of animals and also in human beings. Legionella and Mycobacterium
avium complex (MAC) are environmental pathogens and found have ecological
micro in drinking and hot water supplies.
30
Leptospira: It can survive in ponds, river surface water, and moist soil and in mud
when environment temperature is warm. The bacteria causes abortion, still birth,
agalactia, influenza like illness, nephritis in pups, chronic renal disease in dogs,
septicaemia in calves, piglets and lambs. In dog and human it causes jaundice
and hepatitis.
Vibrio spp: Mostly found in brackish and salt water. The emergence in early 1992
of serotype O139 of Vibrio cholerae with epidemic potential in Southern Asia
suggests that other than V. cholerae 01 could also getting on epidemic. Along with
important human pathogen Vibrio cholerae, there are five more species, which
cause enteric infections. Vibrio cholerae is the major pathogen of human beings
causing cholera. Vibrio metschnikovii causes enteric disease in chickens. Vibrio
anguillarum and some Vibrio spp are pathogens of fish.
Escherichia coli: The bacteria have a worldwide distribution, inhabit the intestinal
tract of human and animals and contaminate vegetation, soil and water. Such
water becomes the most frequent source of infection. Colonization of the intestinal
tract by E. coli from environmental sources occurs shortly after birth. These
organisms persist as important members in the intestine as normal microflora
throughout life. Most strains of E. coli are of low virulence but may cause
opportunistic infection in extra intestinal locations such as the mammary gland
and urinary tract. Pathogenic strains of E. coli possess virulence factors, which
allow them to colonize mucosal surfaces and subsequently produce disease.
The main categories of pathogenic strains of E. coli and their clinical effects are as
followsEnteric disease
Enterotoxigenic E. coli (ETEC): It produces heat labile (LT) and heat stable (ST)
enterotoxins. LT induces hypersecretion in gut and ST reduces absorption leading
to diarrhoea in neonatal piglets, calves and lambs; also causes post- weaning
diarrhoea in pigs.
Enteropathogenic E. coli (EPEC): Although nature of toxins of these organisms
are uncertain but they are found to cause destruction of microvilli, atrophy and
shedding of enterocytes leading to maldigestion, malabsorption and diarrhoea in
piglets, lamb and pups.
31
Vreotoxigenic E. coli (VTEC): It binds to enterocytes and produces verotoxins
viz: VT1, VT2, VT2e leading to damage to vasculature in intestine and in other
locations and causes oedema disease in pigs, haemorrhagic enterocolitis in
calves, post- weaning diarrhoea in pigs and heamorrhagic colitis-haemolytic
uraemic syndrome in man.
Necrotoxigenic strains of E. coli: These organisms binds to enterocytes and
produces cytotoxic necrotizing factors CNF1 and CNF2 leading to damage to
enterocytes and blood vessels and ultimately causes haemorrhagic colitis in
cattle, enteritis in piglets and calves, diarrhoea in rabbits and dysentery in horses.
Septicaemia: Septicaemic strains of E. coli invade blood stream and causes
colisepticaemia in calves, piglets, pups and chickens and watery mouth in lambs
and arthritis and meningitis in many species.
Non enteric localized disease caused by E. coli:
Uropathogenic strains of E. coli: For these bacteria adhesion is required for
colonization. Local reaction attributed to endotoxin and exotoxin and causes
cystitis in many bitches.
Invasion by opportunistic E. coli: They can cause coliform mastitis in cattle and
sows, pyometra in bitches and omphelitis in calves, lambs and chicks if they get
entry inside the organ.
Salmonella: The serotypes occur worldwide and infect many mammals, birds,
and reptiles and mainly excreted in faeces. Ingestion is the main route of infection.
The organism may be present in water, soil, and raw meat, offal and in vegetable
material.
Source
of
environmental
contamination
is
invariably
faeces.
Salmonellosis is of common occurrence in animals and human and the
consequences of infection range from sub-clinical carrier state to acute fatal
septicaemia. Salmonella serotypes of clinical importance are as follows:
Serotype
Species affected
Disease/ syndrome
Salmonella
Typhimurium
Humans
Animals
Food poisoning
Enterocolitis and septicaemia
Salmonella Dublin
Cattle
Septicaemia, abortion, joint
osteomylitis and dry gangrene
Enterocolitis and septicaemia
Sheep, horses and
dogs
ill,
32
Salmonella
Choleraesuis
Pigs
Enterocolitis and septicaemia
Salmonella Pullorum
Chicks
Bacillary white diarrhoea
Salmonella
Gallinarum
Adult birds
Fowl typhoid
Salmonella Arizonae
Turkeys
Paracolon infection
Salmonella Enteritidis
Poultry
Mammals
Humans
Sub-clinical infection
Clinical infection
Food poisioning
Salmonella
Brandenburg
Sheep
Abortion
Corynebacterium: It is a gram-positive pleomorphic bacterium that can survive
for months in the environment. C. pseudotuberculosis causes caseous
lymphadenitis in sheep and goat and ulcerative lymphadenitis in horse and cattle.
It is prevalent in Australia, New Zealand, Middle East, Asia, Africa and North and
South America.
Erysipelothrix rhusiopathiae: Soil and surface water become contaminated with
the organism mainly with pig faeces. Bacteria are often present in the slime layer
of fish, a potential source of human and animal infection. In sheep the bacteria
causes polyarthitis, post-dipping lameness, pneumonia and valvular endocarditis.
In case of human beings the organism affects mainly workers of fish and poultry
industry or agriculture based occupation. The organism enters through minor cuts
and aberration in the skin and leads to local cellulitis known as erysipeloid. In rare
cases disease extends to blood leading to joint and heart involvement.
Bacillus: The bacteria are sporulated and thus persist in soil and water for a long
time. B. anthracis causes anthrax in cattle, sheep, horse and pigs. In human
beings the bacteria causes cutaneous, pulmonary and intestinal form of anthrax.
Another species, B. cereus causes mastitis in cattle and food poisoning and eye
infection in human. The significance of Aeromonas species in the drinking water to
the occurrence of acute gastroenteritis need to be evaluated by further
epidemiological studies.
Shigella: The organism essentially S.sonnei causes bacillary dysentery; stool
containing blood and mucus along with heavy inflammation of colonic mucosa, in
human, chimpanzees and monkeys. The organism is transmitted by oral-faecal
route. Shigella can be found in surface water and drinking water and is highly
33
significant mode of transmission in developing countries. Within clean water the
organism may survive from 14 days to several weeks (Percival et al. 2004).
In addition Giardia, Cryptosporidium, some species of genera Cyclospora,
Isospora and of family Microsporidia are emerging as opportunistic pathogens and
may have waterborne routes of transmission.
Water borne viral diseases : A relatively small group of viruses have been
incriminated as cause of acute gastroenteritis in humans and fewer have proven
to be true etiologic agents, including rotavirus, calcivirus, astrovirus, and some
adenoviruses. More than 15 different groups of viruses, encompassing more than
140 distinct types can be found in the human get.
Avian Influenza viruses:
Avian Influenza virus has caught attention of the whole world in recent
times. These viruses belong to family Orthomyxoviridae and infect domestic birds,
wild waterfowls, humans, sea mammals, horses, felines and pigs (Webster, 1997).
Wild waterfowls are the known carriers, which carry these viruses in their gut
across the continents. They are usually asymptomatic carriers but mortality has
been observed in recent outbreaks among these birds also. This virus replicates
in gut, which is in contrast to human influenza viruses (Gupta, 2005). The virus is
excreted in large quantity from nasal and oral secretions and cloaca of affected
birds. Infected waterfowl may be able to excrete up to 3× 109 EID50 of virus per
gram of faeces.
Infection to domestic birds occurs by mixing of these wild birds with local
population or droppings of these birds may contaminate the water sources. Avian
influenza viruses do not affect human population directly. Infection to humans is
spread only after gene assortment with human influenza viruses in swine
(Webster, 1997). But in recent outbreaks with H5N1 subtype direct transmission to
human beings has been recorded. Therefore, it is possible that humans may get
this infection directly from contaminated water bodies. Virus is also excreted in the
faeces of affected human beings.
Picornaviruses:
These viruses belong to Picornaviridae family (Murphy et al. 1999 e).
Following Genera of this family are transmitted through water:
34
1. Apthovirus:
Foot and mouth disease virus (FMD) affects cloven-hoofed animals. Besides
other routes of transmission, it is also transmitted by contaminated waters
(Schijven et al., 2005).
Equine rhinovirus I causes disease similar to FMD virus in equines.
2. Enterovirus:
Human poliomyelitis: Polio is a highly contagious disease. Poliovirus can survive
in the body, and in raw sewage or freshwater systems; polio is frequently found in
areas where raw sewage directly enters a water source without treatment.
Transmission of the virus occurs either by direct person-to-person contact, or by
indirect contact with infectious saliva or faeces, or with contaminated sewage or
water (Cliver, 1997; Thapliyal, 1999).
Porcine polioencephalomyelitis: causative agent is porcine enterovirus I.
Avian encephalomyelitis causes high morbidity and mortality in affected flock.
Mode of transmission is by faecal-oral route (Murphy et al. 1999 e).
VIRAL GASTROENTERITIS:
Rotaviruses:
Rotaviruses belong to RNA virus family Reoviridae (Murphy et al. 1999a).
Infection has been reported all over the world. These are classified into seven
groups; from A to G. Transmission is through faecal-oral route. Virus is excreted in
the faeces of infected animals in high titers. Virus can survive in the faeces for
several months. Therefore, contaminated water and poor sanitary conditions are
responsible for its transmission. Group A viruses affect multiple species of
mammals and birds. Group B viruses show species specificity. They may infect
cattle, sheep, swine and man. Group C viruses are present in swine and man,
group E viruses in swine whereas group D, E and F affect chickens (Thapliyal,
1999; Hill-king, 2005). The virus affects villi of proximal part of small intestine
resulting in malabsorption and severe diarrhoea.
In animals, disease is referred as white scours or milky scours and mainly
affects young ones. Faeces of affected animals are voluminous soft or liquid.
Young animals may die as a result of dehydration or secondary bacterial infection
(Murphy et al., 1999 a).
35
In human beings it accounts for significant proportion of diarrhoea cases in
children. It affects children during Ist four weeks of life. Death may occur due to
dehydration (Hill-king, 2005).
Caliciviruses:
Water borne caliciviruses have been incriminated in the cases of diarrhoea
in adults and older children. These RNA viruses are the members of the family
Caliciviridae (Murphy et al. 1999 b). Calciviruses and some protozoan agents
such as Cryptosporidium, are the best candidates to reach the highest levels of
endemic transmission, because they are ubiquitous in water intended for drinking,
being highly resistant to chemical disinfecting procedures.
Norovirus: These were earlier known as Norwalk virus and Norwalk like viruses
and are recognized as major causes of water-borne illnesses world-wide. Main
feature of these infections is severe vomiting. Aerosol infection may also occur
(Hederberg and Osterholm, 1993).
Sappovirus: Main feature of infection is persistent watery diarrhoea. It can infect
young children also. Virus is excreted in the faeces of affected persons. Mortality
is usually less.
Adenoviruses:
These are the members of family Adenoviridae (Murphy et al., 1999c).
Enteric adenoviruses of human beings are second most common cause of viral
diarrhoea. These enteric viruses are usually non- cultivable and cause severe
watery diarrhoea in children of one to two years of age. Infection is usually faecooral but nosocomial infection may also occur through contaminated fomites. Virus
is excreted in faeces and urine (Hill-king, 2005).
In animals and birds these are associated with respiratory and gastrointestinal tract infections (Murphy et al., 1999c).
Infectious canine hepatitis: Fever, vomiting, diarrhoea, petechial haemorrhages
and jaundice in pups mark canine adenovirus-1 infection. Virus is excreted in high
concentration in faeces.
Fowl adenoviral infections: fowl adenoviruses have been categorized in three
serogroups.
36
Group I adenoviruses are associated with fowl, geese, ducks and turkeys.
In fowls, 12 serotypes of this virus are associated with inclusion body hepatitishydropericardium syndrome. Virus has natural tropism for liver of poultry. The
disease is characterized by hydropericardium, severe hepatitis, anaemia and
sometimes-yellowish diarrhoea. Mortality is usually high in broiler birds.
Group II adenoviruses are associated with haemorrhagic enteritis of
turkeys and marble spleen disease of pheasants. The disease is usually acute
and there is sudden onset of bloody diarrhoea.
Group III adenoviruses are associated with egg-drop syndrome in poultry.
Virus infects the pouch shell gland of oviduct resulting in decreased thickness of
eggs.
Equine adenoviruses: sometimes cause mild diarrhoea in horses.
Astroviruses:
These RNA viruses are the members of Astroviridae family. These have
wide host range and are present in gastrointestinal tract of young ones of almost
every mammalian species and young ducklings. Affected animal may develop
mild diarrhoea which is not life threatening. But in ducklings of less than 6 week of
age it may cause severe hepatitis (Murphy et al., 1999d). In human beings, it
usually infects children and diarrhoea is of mild nature (Hill-King, 2005).
VIRAL HEPATITIS:
Hepatitis A, Hepatitis E and Hepatitis F viruses are transmitted by
contaminated water (Cliver, 1997). Hepatitis A virus (HAV) and Hepatitis E virus
(HEV) known to cause illness unrelated to the get epitheliums. Numerous large
outbreaks have been documented in the U.S. between 1950 and 1970, and
incidence rate has strongly declined in the developing countries since the 1970s.
Hepatitis E is mostly confined to tropical and subtropical areas, but recent reports
indicate that it can occur at a low level in Europe. These cause mild form of
hepatitis in adult humans. Hepatitis E virus may sometimes cause fatal disease in
pregnant ladies. Infection in children is usually asymptomatic. Virus is excreted in
the faeces.
Water-borne epidemics and health hazards in the aquatic environment are
mainly due to improper management of water resources. Proper management of
37
water resources has become the need of the hour as this would ultimately lead to
a cleaner and healthier environment (Mara and Huran, 2003). In order to prevent
the spread of water-borne diseases, people should take adequate precautions.
The city water supply should be properly checked and necessary steps be taken
to disinfect it. Water pipes should be regularly checked for leaks and cracks. At
home, the water should be boiled; filtered or other necessary steps should be
taken to ensure that it is free from infectious agents (Environmental protection
agency 1975).
References:
Cliver, D.A. (1997). Viral transmission via food. Food tech. 51 (4): 71-78.
Gupta, S. and Arvind Nath (2005). Human disease due to an ‘avian influenza’
virus: The influenza (H5N1) virus. ICMR bulletin 34(2-3): 13-18.
Environmental Protection Agency. 40 CFR Part 141. Water programs: national
interim
primary
drinking
water
regulations.
Federal
Register
1975;40:5956674.
Hederberg, C.W. and Osterholm, M.T. (1993). Outbreak of food-borne and water
borne viral gastroenteritis. Clinic. Microbial. Rev. 6(3). 199-210.
Hill-king, L. (2005). Viral diarrhea. The biomedical scientist 5: 462-466.
Leclerc, H. Schwartzbrod, L. and Dei-Cas, E. (2002). Microbial agents
associated with Waterborne diseases. Crit Rev Microbial. 28(4): 371-409
Mary, A and Ross, M.A. (1996) Microbiological water pollution. Health effect
review 1(7). Pp 1-2
Mara D. and Huran N. (2003). Faecal indicator organism. In: Handbook of water
and water born disease. Academic press. Pp193-208
Murphy, F.A.; Gibbs, E.P.J.; Horzinek, M.C. and Studdert, M.J. (1999a).
Reoviridae. In: Veterinary Virology. 3rd edn. Academic press. Pp 391-404.
Murphy, F.A.; Gibbs, E.P.J.; Horzinek, M.C. and Studdert, M.J. (1999b).
Caliciviridae. In: Veterinary Virology. 3rd edn. Academic press. Pp 533-542.
Murphy, F.A.; Gibbs, E.P.J.; Horzinek, M.C. and Studdert, M.J. (1999c).
Adenoviridae. In: Veterinary Virology. 3rd edn. Academic press. Pp 327334.
38
Murphy, F.A.; Gibbs, E.P.J.; Horzinek, M.C. and Studdert, M.J. (1999d).
Astroviridae. In: Veterinary Virology. 3rd edn. Academic press. Pp 543-545.
Murphy, F.A.; Gibbs, E.P.J.; Horzinek, M.C. and Studdert, M.J. (1999e).
Picornaviridae. In: Veterinary Virology. 3rd edn. Academic press. Pp 391404.
Percival S.L., Chalmers R.M., Embrey M. Hunter P.R., Sellwood and WynJones P. (2004). Shigella species. In: Microbiology of water born disease.
Academic press. Pp 185-196
Pontius F.W., Roberson J.A. (1994) The current regulatory agenda: an update.
Journal of the American Water Works Association.86:54-63.
Quinn P.J., Markey B.K., Carter M.E., Donnelly W.J.C. and Leonard
F.C..(2002) Clostridium species. In: Veterinary Microbiology and Microbial
Disease.Pp63-106
Schijven, J., Rijs, G. B. J. and De Roda Husman A. M. (2005). Quantitative Risk
Assessment of FMD virus transmission via water. Risk analysis 25 (1). 1321.
Thapliyal, D.C. (1999). Diseases caused by viruses. In: diseases of animals
transmissible to man. 1st edn. International book distributing company,
Lucknow. Pp. 57-71.
Webster, R.G. (1997). Influenza virus: transmission between species and
relevance to emergence of the next human pandemic. Arch. virol. suppl.
13. 105-113.
39
Microbiological Analysis of Narmada River: A Case Study
Anjana Sharma
Bacteriology Lab, Department of Biosciences,
R.D. University, Jabalpur (M.P.) India
River Narmada (21o23i to 24o46i N latitude, 72o32i to 81o 46i E Longitude) is the
largest west flowing and the fifth largest river in Peninsula. The total length of the
river from the head to its outfall into the sea is 1312 km. The first 1077 km is in
M.P, the next 35 km forms boundary between the states of Madhya Pradesh and
Maharashtra further 39 km from the boundary between Maharashtra and Gujarat
and the rest of the 161 km lies in Gujarat. The basin had an elongated shape
almost like a thin ribbon with a maximum length of 953 km east to west and a
maximum width of 234 km north to south.
River was divided into 11 different stations for the complete study from its
origin to end viz. Amarkantak, Dindori , Mandala, Jabalpur, Narsinghpur,
Hoshangabad , Omkareshwar, Koral, Neelkantheshwar, Ankleshwar and Dahez
was investigated for its Physicochemical and Bacteriological status.
We screened the river for seven very important genera of pathogenic
potential belonging to the family Aeromonadaceae, Enterobacteriaceae and
Vibrionaceae viz. Aeromonas, Enterobacter, Serratia, Shigella, Salmonella,
Klebsiella and Vibrioand were identified on the basis of biochemical serological &
molecular
techniques.These
investigated for their
clinically
significant
microorganisms
were
enzymatic reactions, antibiotic sensitivity/resistance,
hemolytic activity, complement sensitivity/resistance, virulent genes.
All the species showed multidrug resistance and the plasmid detected
among the isolates were diverse.We screened several virulent genes viz. ipaH,
ipaBCD and STX 1 in Shigella species, ctx A, tcp A (classical), tcp A(ESTor) and
ompW in Vibrio species, STX 2 gene in Enterobacter isolates, act, hly A and βhemolysin was found in Aeromonas isolates. Aeromonas, Enterobacter and
Serratia isolates showed complement sensitivity. Phylogenetic diversity of all the
three families was investigated using 16S rRNA analysis. This demonstrated the
dynamic nature of the population structure and the high level of inter and intra
specific diversity of microorganism in river Narmada.
40
The microbiological standards for fresh water have been the cornerstone
of one of the oldest and the most effective programme for the control of the
infectious diseases. Since the pathogenic organisms studied, are autochthonous
inhabitants of the aquatic environment, the traditional population indicators cannot
access the pollution status of the river water.
41
Modern Molecular Tools & Techniques for Detection of
Water Borne Pathogens
Anil Kumar
Professor & Head
Dept of Molecular Biology & Genetic Engg.,
College of Basic Sciences & Humanities,
G.B. Pant Univ. of Agri. & Technology, Pantnagar
"Today we saw our first public water tap. It is now
rather run down, but looked like it was beautiful at one time. The
spouts were decorated with dragon heads. While we were there a woman
with an aluminum jar came to collect some water to take home with her"
Annette Dietz
Introduction:
Increases in population over the past century have placed tremendous
pressures on water resources of both the developed and developing world. These
pressures include direct contamination from domestic, industrial, and agricultural
wastes and less direct effects caused by climate change and other ecological
disturbances. Population projections for the next century suggest that these
pressures can only increase without appropriate intervention. Development,
implementation, and maintenance of low cost, low technology water treatment
systems are critical for reduction of global mortality associated with waterborne
diseases. Waterborne diseases cannot be eradicated because of the variety of
disease agents transmitted by water. Waterborne diseases must be made
reportable with active surveillance implemented as well as improved risk
assessment methodology used.
Waterborne diseases: A status
Paul R. Hunter, consultant medical microbiologist and director of the
Chester Public Health Laboratory and honorary professor of epidemiology and
public health at the University of Central Lancashire, presented World Health
Organization data that showed high morbidity and death rates worldwide due to
consumption of unsafe drinking water. Currently, about 20% of the world’s
population lacks access to safe drinking water, and more than 5 million people die
annually from illnesses associated with unsafe drinking water or inadequate
sanitation. If everyone had safe drinking water and adequate sanitation services,
42
there would be 200 million fewer cases of diarrhea and 2.1 million fewer deaths
caused by diarrheal illness each year. The wide variety of microbes recognized
since 1980 as waterborne disease agents, including Cryptosporidium, Cyclospora,
Escherichia coli O157:H7, Legionella, Helicobacter pylori, hepatitis E virus,
Toxoplasma, and others in developed country.
Water-borne diseases are among the most recent emerging and reemerging infectious diseases throughout the world and have recently proven to be
the biggest health threat worldwide and they contribute between 70- 80% of health
problems in developing countries. The most well known water-borne diseases
such as cholera, dysentery, and typhoid are the leading causes of morbidity and
mortality. The causative agents of water-borne diseases may be bacterial, viral
and protozoal in nature, and this is true during both epidemic and endemic
periods. The burden of these diseases is most felt in almost all African countries,
especially in the tropical areas of the region, including Kenya. The bulk of these
have been reported from the other countries in the tropical rain forests, e.g.,
Tanzania, Uganda and the Central African Republic, Rwanda and Burundi,
however, the extent of their problem had not been clearly defined within the health
facilities. Accessibility of safe drinking water, particularly among the low-income
communities is still a problem in developing countries. Water supply falls short of
demand, resulting in many residents using less than what is considered sanitary.
Poor waste disposal mechanisms in both urban and rural areas are below
satisfactory requirements, and this contributes in the pollution of water sources in
the district.
Disease causing waterborne pathogens:
The following is a list of some of the disease-causing micro-organisms that
have been reported or known to cause infection in people after exposure to
contaminated water or food.
Bacteria
The following is a list of the 8 main genera of waterborne bacteria that are
harmful to humans. Symptoms include dysentery, vomiting and anorexia. These
genera are as given below:
•
Leptospira
•
Mycobacterium avium complex
43
•
Pseudomonas
•
E. coli
•
Vibrio
•
Salmonella
•
Campylobacter
•
Francis Ella Tulare sis
Viruses
The following is a list of the 6 groups of viruses which cause gastroenteritis. These
have all been found and isolated in contaminated drinking water and beaches.
Symptoms include acute vomiting and mild to severe dysentery.
•
Rotaviruses
•
Norwalk-like agents
•
Caliciviruses
•
Astroviruses
•
Small Round Structured Virus (SRSV)
•
Enteric Adenoviruses
Protozoa
The following is a list of the 3 main genera of waterborne protozoa that are
harmful to humans. They exist independently of the host and are spread through
fecal contact. Symptoms include dysentary, vomiting and anorexia.
•
Giardia
•
Entamoeba
•
Cryptospordium
Non Dysentery Diseases
This is a list of diseases that do not cause dysentery, but do pose a threat
to humans and can be present in contaminated drinking water. Symptoms include
lung, liver damage and Weil's disease.
•
Legionellosis
•
Leptospirosis
•
Hepatitis A
44
Assessment of water quality
For
over
a
century
we
have
been
making
measurements
of
microorganisms in water to help lower the incidence of water borne diseases. In
some cases this is due to limited water surveillance and water treatment
necessary to ensure the microbiological safety of water, but in other cases it is the
result of the inadequacy of the methodologies that are used to monitor water
quality or failures of water treatment systems. Current methods tend to rely upon
indicators, which offer a good margin of safety against most bacterial pathogens
but are not effective protectors against some other bacteria (Campylobacter jejuni,
Salmonella typhimurium, E. coli, Giardia, Cryptosporidium) viruses, and protozoan
parasites. Thus, there is a need to examine newer approaches to monitor the
microbiological quality of water that will lead to a reduction of waterborne disease
transmission.
To be useful, any methodologies for assaying microbial water quality must
fulfill the needs of public health and environmental regulators who are charged
with oversight of drinking water safety. It is essential when developing molecular
methodologies for assessing microbial quality of water that they meet real world
needs. The ultimate measure of the value of molecular methodologies is whether
they represent improvements over conventional methodologies in terms of
achieving a reduction of waterborne diseases and an improvement of human
health. Molecular technologies present powerful new tools for assessing the
microbial quality of water but their current application to water is very limited.
There is a need to define the differing requirements for testing of microorganisms
inclusive of the detection of appropriate indicator or specific microorganisms in
source waters, the application of detecting microorganisms for the assessment of
treatment performance.
Limitations of conventional methods:
Monitoring and regulation of the microbiology relevant to public health in
warm-water recreational pools and other environments has relied primarily on
culture-based analyses that specifically target classical indicator organisms.
Culture can be successful for assessment of some microbes. Traditional
microbiological techniques for the isolation and identification of bacteria from
water have depended on obtaining pure cultures. Enrichment and selection step
45
are often time consuming and the biochemical identification of a particular species
may add several days to the procedure. Such methods are insufficient and
inadequate when outbreaks of water borne disease are occurring. A large body of
gene sequence-based studies shows that standard enrichment techniques
significantly underestimate the actual quantity and diversity of microorganisms in a
wide variety of environments. DNA hybridization methods first developed for
research use in the molecular biology, such as DNA gene probes used for colony
hybridization and the polymerase chain reaction have shorten the time required
for analysis, by obviating the need for pure cultures.
Molecular method for detection:
Detection and identification of micro-organisms are disciplines that
complement each other in order to present a classification system that serves
both applied and general microbiologists. For detection of waterborne pathogens
some basic steps are necessary which are shown as flow chart:
Sample Collection
Sample Storage
Sample
Preparation
Detection and
Analysis
Result
Interpretation
The foremost element to be taken into account in the development and application
of analytical methods in molecular diagnostics is the sample preparation.
46
Discussion of some of these methods is relevant at this stage because many of
them are distinguished by the relative lack of sample preparation required before
the analysis can be performed. However, some methods do require the sample
preparation for biological amplification. The biological amplification comprises of
extraction stage and culture of pathogen on an enriched medium.
The recent and rapid pace of developments in molecular biology has
provided new opportunities in diagnostic areas. Modern diagnostic methods are
based on high affinity biomolecular interaction between ligand and binder. These
include the nucleic acid hybridization (DNA based) and antibody based techniques
involving complementary interaction of DNA-DNA, DNA-RNA, RNA-RNA and
antigen –antibody (Ag – Ab) interactions that have been applied to diagnostics of
water borne pathogens.
1. Membrane filter detection:
The most common indicator of potential pathogen contamination is still the
coliform test in its various guises. The Total coliform test has many forms; the
most common so far has been the membrane filter method in which a known
volume of water is filtered through a 0.45 µ or 0.22 µ filter and the filter incubated
on M-endo or LES-Endo agar. Red colonies with a metallic sheen are considered
coliforms. A variant of this test (the Colilert method) uses ortho-nitrophenyl-betaD-galactosidase (ONPG) and 4-methyl umbelliferyl-beta-D-glucuronide (MUG) for
detecting total coliforms and Escherichia coli in a single solution. The coliforms
break down ONPG with their beta-galactosidase enzymes releasing the yellow
coloured indicator portion of the molecule. If E. coli is also present, the enzyme
glucuronidase hydrolyzes the MUG to glucuronide and the indicator portion 4methyl-umbelliferone that fluoresces under ultraviolet light. This permits separate
and independent estimates of total coliform and E. coli counts in the same
sample.
2. Immunological detection:
•
Immunomagnetic separation:
Magnetic beads are coated with either antibody or gene probe. These are
then incubated with sample so that binding of specific target take place to the
probe .Bound target can then be removed by magnetic separation of the beads.
The bacterial or bacterial genome can then be detected by other means. This has
47
been applied to the separation of bacteria from water or liquefied samples and will
almost certainly, becomes a standard method for processing of water samples.
The technique encompasses separation, concentration and specificity of
diagnosis.
Fig. Immunomagnetic separation of mycobacterium
•
Immunoassays:
Many immunoassays are now available for detecting for water borne
pathogens. These are dependent on inherent ability of living systems to produce
antibodies against foreign substances (antigens) which are specific for that
antigen. There are three main kinds of antibody preparations: polyclonal
antibodies, monoclonal antibodies (MAb) and recombinant antibodies. It is the
specificity of this interaction that makes it a useful diagnostic tool. These antigens
can be proteins, lipid constituents or nucleic acid. Immunoassays can be in a
number of method formats: Enzyme linked immunosorbent assay (ELISA),
radioimmunoassay (RIA), immunodiffusion, immunoblotting, latexagglutination
and
countercurrent
immunoelectrophoresis(CIE).
Immunofluorescence
and
immunogold labelling methods rely on visualization of the fluorochrome or gold-
48
labelled antibody-antigen interactions by microscopy. These methods can provide
useful information on the nature of the antigen in the test sample. Immunoassays
offer ease of use, relative low cost and the feasibility of testing large number of
specimens rapidly.
3. Nucleic acid based detection:
•
Oligonucleotide-Based Microarrays
Microarrays represent an important advance in molecular detection
technology, allowing the simultaneous detection of specifically labeled DNAs from
many different pathogenic organisms on a small glass slide containing thousands
of surface-immobilized DNA probes. Both basic types of microarrays, i.e.,
immobilized oligonucleotide probes and PCR amplicons, have been used
successfully to detect and/or characterize pathogens. As the sensitivity of
microarrays hybridized with total genomic DNA from complex mixtures is usually
inadequate to provide detection of low pathogen concentrations, the hybridized
DNA (target) usually consists of PCR amplicons. This mode of pathogen detection
necessitates the combination of many PCRs prior to their hybridization on
microarrays. Target DNA amplification with universal primers to ubiquitous genes
prior to microarray hybridization can circumvent this limitation. However, within the
Enterobacteriaceae, 16S rRNA and cpn60 sequences may share sufficient
similarity
to
generate
cross-hybridization
reactions,
even
when
short
oligonucleotides are used as probes.
•
Polymerase chain reaction (PCR):
A detection method has been developed for strict and opportunistic
pathogenic
bacteria
(Salmonella,
enterohemorragic
Escherichia
coli
and
Aeromonas hydrophila) in raw and treated water. This method is composed of a
bacterial DNA purification step followed by PCR detection. Compared to the
traditional culture techniques, this method has an enhanced specificity and
sensitivity. Furthermore, the simple and rapid protocol of the proposed technique
provides results at a fraction of the time required by the traditional culture
techniques (24 hours compared with two to six days). However, unlike the culture
methods, detection by PCR does not provide information related to the viability of
the bacteria, since the detected bacteria can be viable and cultivable, viable but
non-cultivable, or dead. The viability concept is very important for interpreting the
49
detection of pathogenic bacteria in relation to public health issues. To overcome
this limitation, an indirect approach has been developed for assessing the viability
of PCR-detected bacteria from water samples. This method is based on the
analysis of each sample before and after a 20-hour culture step in a non-selective
medium: an increase in the PCR response after cultivation indicates the
occurrence of bacterial multiplication and thus demonstrates the viability of the
detected bacteria.
Single colony selected
Total DNA extraction
PCR with specific primers
PCR+
Salmonella
PCRNot Salmonella
Fig. Flow chart for the detection of salmonella direct DNA detection.
•
IS restriction fragment length polymorphism
IS are short stretches of DNA that have the ability to copy themselves in a
random or semi-random fashion. This means that they are often present in
multiple copies in a bacterial chromosome and the pattern of IS distribution can
vary significantly from one strain to the next. By using restriction enzymes to
specifically cut the bacterial chromosome into fragments, size-separating those
fragments by gel electrophoresis, and then probing the fragments with a labelled
copy of the IS, it is possible to obtain an IS banding pattern or fingerprint for that
50
strain. This technique is used for several environmental mycobacteria. Normally,
MAC isolates can be readily discriminated by RFLP Analytical methods 71
analysis using IS1245 and IS1311 (Guerrero et al. 1995),
•
Inter-insertion sequence polymerase chain reaction
Different strains have varying distances between the IS copies, depending
on the pattern of distribution of each IS within that strain. Inter-IS PCR uses PCR
to amplify between adjacent copies of different IS. Outward facing primers are
designed to each IS type and a PCR is performed on genomic DNA extracted
from the isolate. The resulting amplified DNA fragments are separated and
visualized by gel electrophoresis. This method is rapid and simple to perform. It is
used for genotype analysis of MAC by targeting IS1245 and IS1311 (Picardeau &
Vincent 1996). It also has the advantage of not requiring a high concentration or
high quality DNA. Using this technique, it has been possible to genotype strains of
72 Pathogenic Mycobacteria in Water.
•
Random amplified polymorphic DNA (RAPD)
This technique uses short oligonucleotides of random sequence in a low
stringency PCR reaction to produce a strain-specific pattern of PCR fragments
after gel electrophoresis. It is a rapid test that, like PFGE, requires no prior
knowledge of the strain. RAPD has been used relatively widely and has shown
utility in outbreak investigations (Zhang et al. 2002). There are issues surrounding
the reproducibility of this method but attempts have been made to try and
standardize the procedure (Ramasoota et al. 2001).
•
Multi-locus sequence typing
MLST is a recently developed technique, widely used now for bacterial
molecular epidemiological and population genetics studies (Clarke 2002). The
technique is analogous to Multi-Locus Enzyme Electrophoresis except that the
nucleotide sequences for the genes of housekeeping enzymes are determined
rather than looking for differences in the electrophoretic mobility of the enzymes
themselves. This technique identifies unique combinations of alleles. A strain
displaying a unique allele combination is assigned a sequence type (analogous to
a genotype). The method is quite straightforward. As described for 16SrRNA and
hsp65 sequencing, DNA is extracted from a strain and then PCR is used to
amplify specific gene sequences of approximately 500 bp. It is usual to select
51
seven or more distinct loci. The more loci that are analyzed, the greater the level
of discrimination. The products are then subjected to nucleotide sequencing and
then sequence comparisons are made using combinations of alignment and
phylogenetic software.
•
Adaptation of methods to natural waters:
In addition to this taxonomic ignorance, several unnamed species cannot grow
on presently available culture media, and a number of bacterial cells of culturable
species are in a viable and nonculturable state. Thus, detection of bacterial
species by culture on agar media gives a grossly distorted view of the bacterial
diversity in the environment (including water). Molecular methods targeting nucleic
acids are the necessary tools for unveiling bacterial diversity. Ribosomal
ribonucleic acids are universally present in bacteria, have diversely conserved
portions of their sequences, and occur in about 30 000 copies per cell.
Fluorescent oligonucleotide probes can be devised for in situ hybridization (FISH).
Such probes can react with all bacteria, a given phylogenetic branch, a genus, or
a single species. Different fluorescent labels can be used enabling multicolor
reactions.
Conclusion:
The identification and control of threats posed by waterborne pathogens
will require effective molecular technologies, such as those developed in study,
present potentially new tools for assessing microbial quality of water, their
widespread application to water may depend on several factors. For example, the
detection costs must be low and the benefits must outweigh the continued use of
conventional methods; the molecular methods must be specific for the
microorganisms of concern, which means specifically being able to detect live
organisms capable of causing disease; and the sensitivity must be adequate to
provide protection against water-borne disease, which means being able to
concentrate targets for detection from large volumes of water and to overcome
interfering factors that may be present so as to detect very low numbers of
microorganisms. The studies have shown that it is possible to detect different
types of pathogenic bacteria from water samples within 24 h. The combination of
membrane filtration, an enrichment procedure and PCR provided a sensitive,
specific and easy method for the detection of pathogens in environmental water
samples. Inhibiting substances hampered PCR detection only in a very limited
number of samples and these consisted mainly of drinking water and heavily
contaminated effluents. The inhibitory substances, however, may be removed by
extracting the DNA prior to analysis or by further dilution of the samples.
52
Further readings:
Alm, E. W., D. B. Oerther, N. Larsen, D. A. Stahl, and L. Raskin. 1996. The
oligonucleotide probe database. Appl. Environ. Microbiol. 62:3557-3559.
Bayardelle, P., and M. Zafarullah. 2002. Development of oligonucleotide primers
for the specific PCR-based detection of the most frequent
Enterobacteriaceae species DNA using wec gene templates. Can. J.
Microbiol. 48:113-122.
Bej, A. K. 2003. Molecular based methods for the detection of microbial
pathogens in the environment. J. Microbiol. Methods 53:139-140.
Bej, A. K., J. L. DiCesare, L. Haff, and R. M. Atlas. 1991. Detection of
Escherichia coli and Shigella spp. in water by using the polymerase chain
reaction and gene probes for uid. Appl. Environ. Microbiol. 57:1013-1017.
Bekal, S., R. Brousseau, L. Masson, G. Prefontaine, J. Fairbrother, and J.
Harel. 2003. Rapid identification of Escherichia coli pathotypes by virulence
gene detection with DNA microarrays. J. Clin. Microbiol. 41:2113-2125.
Berthelet, M., L. G. Whyte, and C. W. Greer. 1996. Rapid, direct extraction of
DNA from soils for PCR analysis using polyvinylpolypyrrolidone spin
columns. FEMS Microbiol. Lett. 138:17-22.
Brewster, D. H., M. I. Brown, D. Robertson, G. L. Houghton, J. Bimson, and J.
C. Sharp. 1994. An outbreak of Escherichia coli O157 associated with a
children's paddling pool. Epidemiol. Infect. 112:441-447.
Brousseau, R., J. E. Hill, G. Prefontaine, S. H. Goh, J. Harel, and S. M.
Hemmingsen. 2001. Streptococcus suis serotypes characterized by
analysis of chaperonin 60 gene sequences. Appl. Environ. Microbiol.
67:4828-4833.
Burge, H. (1990) J. Allergy Clin. Immunol. 86, 687-701.
Call, D. R., M. K. Borucki, and F. J. Loge. 2003. Detection of bacterial
pathogens in environmental samples using DNA microarrays. J. Microbiol.
Methods 53:235-243.
Colwell, R. R., Brayton, P. B. & Al., E. (1985) BioTechnology 3, 817-820.
Falkinham, J. O., III. (2003) Emerg. Infect. Dis. 9, 763-767.
Flannigan, B., McCabe, E. M. & McGarry, F. (1991) J. Appl. Bacteriol. Symp.
Suppl. 70, 61S-73S.
Hussong, D., Colwell, R. R., O'Brien, M., Weiss, E. & Pearson, A. D. (1987)
BioTechnology 5, 947-950.
53
Kujundzic, E., Angenent, L. T., Zander, D. A., Henderson, D. E., Miller, S. L. &
Hernandez, M. T. (2005) Air Waste 55, 210-218.
Lemarchand, K., L. Masson, and R. Brousseau. 2004. Molecular biology and
DNA microarray technology for microbial quality monitoring of water. Crit.
Rev. Microbiol. 30:145-172.
Leoni, E., Legnani, P. P., Bucci Sabattini, M. A. & Righi, F. (2001) Water Res.
35, 3749-3753.
McCabe, K. M., Y. H. Zhang, B. L. Huang, E. A. Wagar, and E. R. McCabe.
1999. Bacterial species identification after DNA amplification with a
universal primer pair. Mol. Genet. Metab. 66:205-211.
Milton, D. K. (1999) in Bioaerosols: Assessment and Control, eds. Macher, J.,
Ammann, H. A., Burge, H. A., Milton, D. K. & Morey, P. R. (American
Conference of Governmental Industrial Hygienists (ACGIH), Cincinnati,
OH).
Mukoda, T. J., Todd, L. A. & Sobsey, M. D. (1994) J. Aerosol Res. 25, 15231532.
Pace, N. R. (1997) Science 276, 734-740.
Rose, C. S., Martyny, J. W., Newman, L. S., Milton, D. K., King, T. E., Jr.,
Beebe, J. L., McCammon, J. B., Hoffman, R. E. & Kreiss, K. (1998) Am.
J. Public Health 88, 1795-1800.
Shafer, M. P., Fernback, J. E. & Jensen, P. A. (1998) AIHA J. 59, 540-546.
Sherwood, R. L. (2000) in Pulmonary Immunotoxicology, eds. Cohen, M. D.,
Zelikoff, J. T. & Schlesinger, R. B. (Kluwer, Boston), pp. 181-197.
Swerdlow, D. L., B. A. Woodruff, R. C. Brady, P. M. Griffin, S. Tippen, H. D.
Donnell, Jr., E. Geldreich, B. J. Payne, A. Meyer, Jr., J. G. Wells, et al.
1992. A waterborne outbreak in Missouri of Escherichia coli O157:H7
associated with bloody diarrhea and death. Ann. Intern. Med. 117:812-819.
Van der Giessen, J. W., A. Eger, J. Haagsma, R. M. Haring, W. Gaastra, and
B. A. van der Zeijst. 1992. Amplification of 16S rRNA sequences to detect
Mycobacterium paratuberculosis. J. Med. Microbiol. 36:255-263.
Vora, G. J., C. E. Meador, D. A. Stenger, and J. D. Andreadis. 2004. Nucleic
acid amplification strategies for DNA microarray-based pathogen detection.
Appl. Environ. Microbiol. 70:3047-3054.
54
Tools and Techniques for Purification of Water and
Waste Water
Sanjeev Agrawal
Professor and Head
Department of Biochemistry
College of Basic Sciences & Humanities
G. B. Pant University of Agri. & Tech., Pantnagar-263145
What is pure water?
We know that all life is dependent on water. Water exists in nature in many
forms- clouds, rain, snow, ice and fog. Chemically pure water does not exist for
any appreciable length of time in nature. When water falls as rain, it picks up small
amount of gases, ions, dust and particulate matter from the atmosphere. Then, as
it flows over or through the surface layers of the earth, it dissolves and carries with
it some or almost everything it touches, including that which is dumped into it by
man.
These added substances may be arbitrarily classified as biological,
chemical (both inorganic and organic), physical and radiological impurities. They
include industrial and commercial solvents, metal and acid salts, sediments,
pesticides, herbicides, plant nutrients, radioactive materials, decaying animal and
vegetable matter etc. and cause hardness, corrosiveness, staining or frothing.
They may damage growing plants and transmit disease. Many of these impurities
are removed or rendered harmless in municipal drinking water treatment plants.
The meaning of pure water varies from person to person. Homeowners are
primarily concerned with domestic water problems related to color, odor, taste and
safety to family health. Chemist and engineers working for industry are concerned
with the purity of water as it relates to scale deposition and pipe corrosion.
Regulatory agencies are concerned with setting standards to protect public health.
Farmers are interested in the effect of irrigation water on soil, particularly as they
influence crop production; hence, they are concerned with the water’s total
mineral content, proportion of sodium, or content of ions “toxic” to plant growth.
Chemicals in drinking water which are toxic may cause either acute or
chronic health effect. An acute effect usually follows a large dose of a chemical
55
and occurs almost immediately. Example of acute health effect are nausea, lung
irritation, skin rash, vomiting, dizziness and in the extreme, death. The levels of
chemicals in drinking water however are seldom high enough to cause acute
health effects. They are more likely to cause chronic effects, that occur after
exposure to small amount of a chemical over a long period. Example of chronic
health effects includes cancer, birth defects, organ damage, disorders of the
nervous system and damage to the immune system.
Waste water
On the other hand, waste water is sewage, storm water and water that has
been used for various purposes around the community. Unless properly treated,
waste water can harm public health and environment. Chemically, waste water is
mostly water by weight. Other materials make up only a small portion of waste
water but can be present in large enough quantities to endanger public health and
the environment. Because practically any things that can be flushed down a toilet,
drain or sewer can be found in sewage water. Even house hold sewage contains
many potential pollutants. The waste water components that are most concerned
to the community are those that have the potential to cause diseases or
detrimental environmental effect.
Many different types of organism live in waste water and some are
essential contributors to treatment. A variety of bacteria, protozoa and worms
work to break down certain carbon based (organic) pollutants in waste water by
consuming them. Through this process, organisms turn waste into carbon di
oxide, water or new cell growth.
Many disease causing viruses, parasites and bacteria also are present in
wastewater and enter from almost any where in the community. These pathogens
often originate from people and animals, who are infected with or are carriers of a
diseases. Gray water or black water from typical home contains enough
pathogens to pose a risk to public health. Gastroenteritis can result from a variety
of pathogens in waste water. The cases of illnesses caused by the parasitic
protozoa Giardia lambia and Cryptosporidium are not usual. The other important
waste water related diseases include hepatitis A, typhoid, polio, cholera &
dysentery. Outbreaks of these diseases can occur due to drinking water from
wells gets polluted by waste water, eating contaminated fish or recreational
56
activities in polluted water. Some illness can be spread by animals and insets that
come in contact with waste water. Even municipal drinking water source are not
completely immune to health risks from waste water pathogens.
The water we use never really goes away. In fact, there never will be any
more or any less water on earth than there is right now. Which means that all of
the waste water generated by our communities each day from houses, farms,
business and factories, eventually returns back to the environment to be used
again. So when waste water receives inadequate treatment, the overall quality of
the world’s water supply suffers.
The waste water treatment is a relatively recent practice? Prior to the mid
1800’s human and other wastes usually were just dumped or conveyed to the
nearest body of water without treatment. As a result, ground water and other
sources of drinking and bathing were regularly contaminated with sewage.
Epidemics of cholera, typhoid, dysentery and other water born disease killed
thousands and out breaks were especially devastating in densely populated
areas.
After 1854, when the connection between a cholera outbreak and sewage
contaminated water was first discovered, better attempts were made to treat and
dispose of sewage separately from drinking water.
. For this reason, waste
water treatment is as important to public health as drinking water treatment.
Need of water analysis
Clean, fresh drinking water is rapidly becoming a scarce and valuable
resource. There are a long list of common ways in which surface water can
become contaminated and unsafe, such as through the addition of organic wastes
from livestock or even human settlements, through chemical runoff from
agriculture lands or through industrial effluents entering a water source. Point
sources of pollution, such as pipes discharging contaminated water from a factory
into a stream are relatively easy to identify. Non-point pollution sources, such as
agriculture runoff that may have many pathways by which it enters a surface water
supply, are vary hard to manage. It is becoming necessary to test fresh water
streams and reservoirs regularly in order to determine their quality and detect any
new contamination from point or non-point sources.
57
Water quality assessment
Chemical attributes of a waterway can be important indicators of water
quality. Chemical attributes of water can affect aesthetic qualities such as how
water looks, smells and tastes. Chemical attributes of water can also affect its
toxicity and whether or not it is safe to use. Since the chemical quality of water is
important to the health of humans as well as the plants and animals that live in
and around streams, it is necessary to assess the chemical attributes of water.
Assessment of water quality by its chemistry includes measures of many
elements of molecules dissolved or suspended in the water. Chemical measures
can be used to directly detect pollutants such as lead or mercury. Chemical
measures can also be used to detect imbalances within the ecosystem. Such
imbalances may indicate the presence of certain pollutants. For example, elevated
acidity levels may indicate the presence of acid mine drainage.
Commonly measured chemical parameters include pH, alkalinity, hardness,
nitrates, nitrites and ammonia, ortho- and total phosphates and dissolved oxygen
and biochemical oxygen demand. The presence of fecal coliform, bacteria is also
determined using a chemical test. This microscopic organism is too small to detect
during the biological assesment.of macroinvertebrate populations. In addition,
some “chemical” measurements actually indicate the physical presence of
pollutants in water. These include measurement such as conductivity and density.
Wastewater quality indicators
Any oxidizable material present in a natural waterway or in an industrial
wastewater will be oxidized both by biochemical (bacterial) or chemical processes.
The result is that the oxygen content of the water will be decreased. Basically, the
reaction for biochemical oxidation may be written as:
Oxidizable material + bacteria + nutrient + O2 → CO2 + H2O + oxidized
inorganics such as NO3 or SO4
Oxygen consumption by reducing chemicals such as sulfides and nitrites is
typified as follows:
S-- + 2 O2 → SO4-NO2- + ½ O2 → NO3Since all natural waterways contain bacteria and nutrient, almost any waste
compounds introduced into such waterways will initiate biochemical reactions
58
(such as shown above). Those biochemical reactions create what is measured in
the laboratory as the Biochemical oxygen demand (BOD).
Oxidizable chemicals (such as reducing chemicals) introduced into a
natural water will similarly initiate chemical reactions (such as shown above).
Those chemical reactions create what is measured in the laboratory as the
Chemical oxygen demand (COD).
Both the BOD and COD tests are a measure of the relative oxygendepletion effect of a waste contaminant. Both have been widely adopted as a
measure of pollution effect. The BOD test measures the oxygen demand of
biodegradable pollutants whereas the COD test measures the oxygen demand of
biogradable pollutants plus the oxygen demand of non-biodegradable oxidizable
pollutants.
The so-called 5-day BOD measures the amount of oxygen consumed by
biochemical oxidation of waste contaminants in a 5-day period. The total amount
of oxygen consumed when the biochemical reaction is allowed to proceed to
completion is called the Ultimate BOD. The Ultimate BOD is too time consuming,
so the 5-day BOD has almost universally been adopted as a measure of relative
pollution effect.
There are also many different COD tests. Perhaps, the most common is the
4-hour COD.
It should be emphasized that there is no generalized correlation between
the 5-day BOD and the Ultimate BOD. Likewise, there is no generalized
correlation between BOD and COD. It is possible to develop such correlations for
a specific waste contaminant in a specific wastewater stream, but such
correlations cannot be generalized for use with any other waste contaminants or
wastewater streams.
Water purification
Water purification is the process of removing contaminants from a raw
water source. The goal is to produce water for a specific purpose with a treatment
profile designed to limit the inclusion of specific materials; most water is purified
for drinking purpose. It may also be purified
for a variety of other purposes,
including to meet the requirements of medical, pharmacology, chemical and
industrial applications. Methods include ultra violet light, filtration, water softening,
59
reverse osmosis, ultrafiltration, molecular stripping, deionization, and carbon
treatment.
Water purification may remove: particulate sand; suspended particles of organic
matter; Parasites, Giardia; Cryptosporidium; bacteria; algae; virus; fungi; etc.
Minerals calcium, silica, magnesium, etc., and Toxic metals lead; copper;
chromium; etc. Some purification may be elective in the purification process,
including smell (hydrogen sulfide remediation), taste (mineral extraction), and
appearance (iron incapsulation).
Governments usually dictate the standards for drinking water quality. These
standards will require minimum / maximum set points of contaminants and the
inclusion of control elements that produce potable drinking water.
Ground water (usually supplied as well water) is typically a more economical
choice than surface water (from rivers, lakes and streams) as a source for
drinking, as it is inherently pre-filtered by the aquifer from which it is extracted.
Over large areas of the world, aquifers are recharged as part of the hydrologic
cycle.
It is not possible to tell whether water is safe to drink just by looking at it.
Simple procedures such as boiling or the use of a household charcoal filter are not
sufficient for treating all the possible contaminants that may be present in water
from an unknown source.
Widely varied techniques are available to remove the fine solids, micro-organisms
and some dissolved inorganic and organic materials. The choice of method will
depend on the quality of the water being treated, the cost of the treatment process
and the quality standards expected of the processed water.
Distilled water has an average pH of 7 (neither alkaline nor acidic) and sea
water has an average pH of 8.3 (slightly alkaline). If the water is acidic (lower than
7), lime or soda ash is added to raise the pH. Lime is the more common of the two
additives because it is cheaper, but it also adds to the resulting water hardness.
Making the water slightly alkaline ensures that coagulation and flocculation
processes work effectively and also helps to minimize the risk of lead being
dissolved from lead pipes .
Coagulation, flocculation and sedimentation are used in conjunction with
subsequent filtration. Coagulation promotes the interaction of small particles to
60
form larger particles. Flocculation is the physical process of producing interparticle contacts that lead to the formation of large particles. Sedimentation is a
solid-liquid separation process, in which particles settle under the force of gravity.
Most bacteria, viruses and protozoa are eliminated by such processes.
Conventionally, clarification refers to chemical addition, rapid mixing,
flocculation and sedimentation. Here the chemical coagulation is critical for
effective removal of microbial pathogens. Removal of bacteria (E.coli vegetative
cells and clostridium perfringens spores) and protozoa (Giardia cysts and
Cryptosporidium oocysts) is possible but this can be achieved by the use of ironbased coagulants which are slightly more efficient than alum (aluminum
hydroxide) or poly-aluminum chloride (PACI); however, coagulation conditions (i.e.
dose, pH, Temperature, alkalinity, turbidity and the level and type of natural
organic matter) affect the efficiency of removal.
Precipitate lime softening is a process in which the pH of the water is
increased (usually through the addition of lime or soda ash) to precipitate high
concentrations of calcium and magnesium. Removal and reduction in the viability
of Giardia, viruses and coliforms is achieved.
Filtration
After separating most floc, the water is filtered as the final step to remove
remaining suspended particles and unsettled floc. The most common type of filter
is a rapid sand filter. Water moves vertically through sand which often has a layer
of activated carbon or anthracite coal above the sand. The top layer removes
organic compounds, which contribute to taste and odour. The space between
sand particles is larger than the smallest suspended particles, so simple filtration
is not enough. Most particles pass through surface layers but are trapped in pore
spaces or adhere to sand particles. Effective filtration extends into the depth of the
filter. This property of the filter is key to its operation: if the top layer of sand were
to block all the particles, the filter would quickly clog. To clean the filter, water is
passed quickly upward through the filter, opposite the normal direction (called
backflushing or backwashing) to remove embedded particles. Prior to this,
compressed air may be blown up through the bottom of the filter to break up the
compacted filter media to aid the backwashing process; this is known as air
scouring. This contaminated water can be disposed of, along with the sludge from
61
the sedimentation basin, or it can be recycled by mixing with the raw water
entering the plant. Some water treatment plants employ pressure filters. These
work on the same principle as rapid gravity filters, differing in that the filter medium
is enclosed in a steel vessel and the water is forced through it under pressure.
Membrane filtration is essentially a thin film of synthetic polymer through
which there are pores of fairly uniform size. This filters water as it flows through.
Membrane filters are widely used for filtering both drinking water and sewage for
reuse.
For drinking water, membrane filters can remove virtually all particles larger
than 0.2 um--including Giardia and Cryptosporidium. Membrane filters are an
effective form of tertiary treatment when it is desired to reuse the water for
industry, for limited domestic purposes, or before discharging the water into a river
that is used by towns further downstream. They are widely used in industry,
particularly for beverage preparation (including bottled water). However no
filtration can remove substances that are actually dissolved in the water such as
phosphorus, nitrates and heavy metal ions.
Ultrafiltration
Ultrafiltration membranes are a relatively new development; they use polymer film
with chemically formed microscopic pores that can be used in place of granular
media to filter water effectively without coagulants. The type of membrane media
determines how much pressure is needed to drive the water through and what
sizes of micro-organisms can be filtered out.
Common microorganisms and the filter size needed:
Organism
Protozoa
Bacteria
Examples
General Size
Giardia,
5 microns or
Cryptosporidium
larger
Cholera, E. coli,
0.2–0.5
Salmonella
microns
Hepatitis A,
Viruses
rotavirus,
Norwalk virus
0.004
microns
Filter Type
Water filter
Microfilter
Water purifier
Particle Size
Rating
1.0–4.0
microns
0.2–1.0
microns
to 0.004
microns
62
Disinfection
Disinfection is normally the last step in purifying drinking water. Water is
disinfected to kill any pathogens which pass through the filters. Possible
pathogens include viruses, bacteria, including Escherichia coli, Campylobacter
and Shigella, and protozoans, including G. lamblia and other Cryptosporidia. In
most developed countries, public water supplies are required to maintain a
residual disinfecting agent throughout the distribution system, in which water may
remain for days before reaching the consumer. Following the introduction of any
chemical disinfecting agent, the water is usually held in temporary storage tank to
allow the disinfecting action to complete. This is done by adding gaseous
dissloved chlorine in the water. Chlorine at a concentration of 1 or 2 ppm destroys
bacteria and some viruses. Sufficient chlorine is added to the water (with careful
monitoring) to ensure that the concentration stays slightly above 1ppm until the
water reaches the end user.
1).
Chlorination- The most common disinfection method is some form of
chlorine or its compounds such as chloramine or chlorine dioxide. Chlorine
is a strong oxidant that kills many micro-organisms. Because chlorine is a
toxic gas, there is a danger of a release associated with its use. This
problem is avoided by the use of sodium hypochlorite, which is either a
relatively inexpensive solid that releases free chlorine when dissolved in
water. The generation of liquid sodium hypochlorite is both inexpensive and
safer than the use of gas or solid chlorine. Both disinfectants are widely
used despite their respective drawbacks. One drawback to using chlorine
gas or sodium hypochlorite is that they react with organic compounds in the
water to form potentially harmful chemical by-products trihalomethanes
(THMs) and haloacetic acids (HAAs), both of which are carcinogenic in
large quantities.
2).
Chlorine dioxide is another fast-acting disinfectant. It is rarely used,
because it may create excessive amounts of chlorate and chlorite.
3).
Chloramines are another chlorine-based disinfectant. Although chloramines
are not as strong of an oxidant or provide a reliable residual, as compared
to chlorine gas or sodium hypochlorite, they are less prone to form THMs or
haloacetic acids.
63
4).
Ozone (O3) is a powerful oxidising agent which is toxic to most water borne
organisms. It is a very strong, broad spectrum disinfectant that is widely
used in Europe. It is an effective method to inactivate harmful protozoans
that form cysts. UV radiation (light) is very effective at inactivating cysts, as
long as the water has a low level of colour so the UV can pass through
without being absorbed. The main disadvantage to the use of UV radiation
is that, like ozone treatment, it leaves no residual disinfectant in the water.
Because neither ozone nor UV radiation leaves a residual disinfectant in
the water, it is sometimes necessary to add a residual disinfectant after
they are used. This is often done through the addition of chloramines.
Additional treatment options
1).
Fluoridation –Addition of fluoride to water for the purpose of preventing
tooth decay.is known as Water fluoridation
2).
Water conditioning: This is a method of reducing the effects of hard
water. Hardness salts are deposited in water systems subject to heating
because the decomposition of bicarbonate ions creates carbonate ions
which crystalise out of the saturated solution of calcium or magnesium
carbonate. Water with high concentrations of hardness salts can be treated
with soda ash (sodium carbonate) which precipitates out the excess salts.
3).
Plumbosolvency reduction: In areas of naturally acidic waters ,the water
may be capable of dissolving lead from any lead pipes that it is carried in.
The addition of small quantities of phosphate ion and increasing the pH
slightly both assist in greatly reducing plumbo-solvency by creating
insoluble lead salts on the inner surfaces of the pipes.
4).
Fluoride Removal: In some areas of the world have excessive levels of
natural fluoride is found in the source water. Excessive levels can be toxic
or cause undesirable cosmetic effects such as staining of teeth. It can be
reduced through treatment with activated alumina.
Other water purification techniques
Other popular methods for purifying water, especially for local private supplies are
listed below. Particularly important are distillation (de-salination of seawater) and
reverse osmosis.
64
1).
Boiling: Water is heated hot enough and long enough to inactivate or kill
micro-organisms that normally live in water at room temperature. Near sea
level, a vigorous rolling boil for at least one minute is sufficient. At high
altitudes (greater than two kilometers or 5000 feet) three minutes is
recommended.
2).
Carbon filtering: Charcoal, a form of carbon with a high surface area,
absorbs many compounds including some toxic compounds. Water passing
through activated charcoal is common in household water filters and fish
tanks. Household filters for drinking water sometimes contain silver to
release silver ions which have an anti-bacterial effect.
3).
Distillation involves boiling the water to produce water vapour. The vapour
contacts a cool surface where it condenses as a liquid. Because the
solutes are not normally vaporised, they remain in the boiling solution.
Even distillation does not completely purify water, because of contaminants
with similar boiling points and droplets of unvaporised liquid carried with the
steam. However, 99.9% pure water can be obtained by distillation.
4).
Reverse osmosis: Mechanical pressure is applied to an impure solution to
force pure water through a semi-permeable membrane. Reverse osmosis
is theoretically the most thorough method of large scale water purification
available, although perfect semi-permeable membranes are difficult to
create. Unless membranes are well-maintained, algae and other life forms
can colonise the membranes.
5).
Ion exchange: Most common ion exchange systems use a zeolite resin bed
to replace unwanted Ca2+ and Mg2+ ions with benign (soap friendly) Na+ or
K+ ions. This is the common water softener.
6).
Electrodeionization: Water is passed between a positive electrode and a
negative electrode. Ion selective membranes allow the positive ions to
separate from the water toward the negative electrode and the negative
ions toward the positive electrode. High purity deionized water results. The
water is usually passed through a reverse osmosis unit first to remove nonionic organic contaminants.
It may be concluded that water is an essential ,precious commodity. It
should be purified before supplying to the community.The water used for the
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purpose of drinking should not only be visibly clean but should also be free from
microbes and other contaminants.The best way to ensure clean water is not to
pollute it. Various processes used for the purification of water suffer from one or
the other lacunae. So we need to use a composite system that can enhance
safety.
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