IMPORTANT

Water Pollution : Quality of sewage : Physical properties,

Chemical properties, Biological characteristics; Sources of
water pollution: Domestic, Industrial and Biological.
Sources of Water Pollution
1. Industrial Waste
Industries produce a tremendous amount of waste, which contains toxic chemicals and pollutants, causing air pollution and
damage to our environment and us. They contain harmful chemicals, including lead, mercury, sulfur, nitrates, asbestos, and
many others.
Many industries, not having a proper waste management system, drain the waste in the freshwater, which goes into canals,
rivers, and later into the sea.
The toxic chemicals may change the colour of water, increase the number of minerals, called eutrophication, change the
temperature of the water, and pose a severe hazard to water organisms.
2. Sewage and Wastewater
The sewage and wastewater that is produced in each household are treated chemically and released into the sea along with
fresh water. The sewage water carries pathogens, a typical water pollutant, other harmful bacteria, and chemicals that can
cause serious health problems and thereby diseases.
Pathogens are disease-causing microorganisms, e.g., viruses, bacteria, parasitic worms, and protozoa, which cause a variety of
intestinal diseases such as dysentery, typhoid fever, and cholera. Pathogens enter water primarily from human and animal
fecal waste due to inadequate sewage treatment. In many underdeveloped countries, sewage is discharged into local waters
either untreated or after only rudimentary treatment. In developed countries untreated sewage discharge can occur from
overflows of combined sewer systems, poorly managed livestock factory farms, and leaky or broken sewage collection systems.
3. Mining Activities
Mining is the process of crushing the rock and extracting coal and other minerals from the underground. These
elements, when extracted in the raw form, contain harmful chemicals and can increase the number of toxic elements
when mixed up with water, which may result in health problems. Mining activities emit a large amount of metal waste
and sulphides from the rocks, which is harmful to the water.
4. Marine Dumping
The garbage produced by households in the form of paper, plastic, food, aluminium, rubber, glass, is collected and dumped into
the sea in some countries. These items take 2 weeks to 200 years to decompose.
When such things enter the sea, they not only cause water pollution but also harm animals in the sea.
5. Accidental Oil Leakage
Oil spill poses a huge threat to marine life when a large amount of oil spills into the sea and does not dissolve in water. It causes
problems for local marine wildlife, including fish, birds, and sea otters.
A ship carrying a large quantity of oil may spill oil if met with an accident. Such an oil spill can cause varying damage to species
in the ocean, depending on the amount of oil spill, the toxicity of pollutants, and the size of the ocean.
6. The burning of fossil fuels
Fossil fuels like coal and oil, when burnt, produce a substantial amount of ash in the atmosphere. The particles which contain
toxic chemicals when mixed with water vapor result in acid rain. Also, carbon dioxide is released from the burning of fossil
fuels, which results in global warming.
7. Chemical fertilizers and pesticides
Chemical fertilizers and pesticides are used by farmers to protect crops from insects and bacteria. They are useful for the
plant’s growth. However, when these chemicals are mixed up with water, they produce harmful pollutants for plants and
animals.
Also, when it rains, the chemicals mix up with rainwater and flow down into rivers and canals, which pose serious damages for
aquatic animals.
8. Leakage from Sewer Lines
A small leakage from the sewer lines can contaminate the underground water and make it unfit for the people to drink.
Also, when not repaired on time, the leaking water can come on to the surface and become a breeding ground for insects
and mosquitoes.
9. Global Warming
An increase in the earth’s temperature results in global warming due to the greenhouse effect. It increases the water
temperature and results in the death of aquatic animals and marine species, which later results in water pollution.
10. Radioactive Waste
Nuclear energy is produced using nuclear fission or fusion. The element that is used in the production of nuclear energy is
Uranium, which is a highly toxic chemical.
The nuclear waste that is produced by radioactive material needs to be disposed of to prevent any nuclear accident.
Nuclear waste can have serious environmental hazards if not disposed of properly. Few major accidents have already taken
place in Russia and Japan.
11. Urban Development
As the population has grown exponentially, so has the demand for housing, food, and cloth. As more cities and towns are
developed, they have resulted in increasing use of fertilizers to produce more food, soil erosion due to deforestation, rise in
construction activities, inadequate sewer collection and treatment, landfills as more garbage is produced, increase in
chemicals from industries to produce more materials.
12. Leakage from the Landfills
Landfills are nothing but a massive pile of garbage that produces the awful smell and can be seen across the city. When it
rains, the landfills may leak, and the leaking landfills can pollute the underground water with a large variety of
contaminants.
13. Animal Waste
The waste produced by animals washed away into the rivers when it rains. It then gets mixed up with other harmful
chemicals and causes various water-borne diseases like cholera, diarrhoea, dysentery, jaundice, and typhoid.
14. Underground Storage Leakage
Transportation of coal and other petroleum products through underground pipes is well known. Accidental leakage may
happen anytime and may cause damage to the environment and result in soil erosion.
15. Eutrophication
The increased level of nutrients in water bodies is known as Eutrophication. It results in the bloom of algae in the water. It
also depletes the amount of oxygen in the water that negatively affects fish and other aquatic animal populations.
16. Acid Rain
Acid rain is essentially water pollution caused by air pollution. When the acidic particles released in the atmosphere by air
pollution mix with water vapor, it results in acid rain.
Characteristics of sewage
I. Physical characteristics of sewage:
1. Temperature:
•Temperature of sewage depends upon season. However temperature is slightly higher than that of ground
water.
•High temperature of sewage is due to evolution of heat during decomposition of organic matter in sewage.
2. Color:
•Color of sewage indicates its strength and age.
•Fresh domestic sewage is grey in color but septic sewage is dark in color
•When industrial effluent is mixed it give characteristic color to sewage
3. Odor:
•Fresh domestic sewage is almost odorless.
•Septic or stale sewage is putrid in odor which is due to generation of H2S during anaerobic decomposition of
organic matters.
•When industrial effluent is mixed, it give characteristics odor to sewage
4. Turbidity:
•Sewage is highly turbid.
II. Chemical characteristics of sewage:
1. Organic matter:
•In general sewage contains large amount of organic matters.
2. Chloride:
•Human beings discharge large amount (8-15gm/day) of chloride in the form of NaCl, especially through urine and
sweat. So domestic sewage from toilet and bathroom contains higher level of chloride.
3.Sulfite:
In sewage sulfite in the form of H2S (hydrogen sulfite) is generated during anaerobic decomposition of organic matters
by anaerobic bacteria.
•H2S gives putrid odor to sewage.
4. Biological oxygen demand (BOD):
•Sewage usually have high BOD due to presence of large amount of organic matters.
•Value of BOD ranges from 100mg/ltr for very dilute sewage to 600mg/ltr or more for concentrated sewage containing
industrial effluent mix.
5. Dissolved oxygen (DO):
•Due to high level of microbial cells and biodegradable organic matters, sewage have very low level of dissolved
oxygen.
•In some sewage, DO is completely absent.
•Level of Do depends on age and condition of sewage. Low level DO is also due to lower solubility of oxygen in
sewage. Oxygen is only 95% soluble in sewage than in pure water).
6. pH:
•sewage is slightly alkaline in pH
III. Biological characteristics of sewage:
1. Bacteria:
•Two types of bacteria are found in sewage.
• Intestinal bacteria:
• Non-pathogenic intestinal bacteria are normal flora of gastrointestinal tract of human and animals
and enter into sewage together with stool. Examples; faecal coliform, faecal streptococci, Clostridium
perfingens, et
• Pathogenic intestinal bacteria such as Salmonella, Shigella, Vibrio cholera, Yersenia enterocolitica etc enter
into sewage through stool of patients.
• Real sewage bacteria
• The natural habitat of these bacteria is sewage.
• Both aerobic as well as anaerobic are found in sewage.
• Aerobic bacteria play important role in oxidation of organic matter during aerobic process.
• Common anaerobic bacteria includes;
• Clostridium sporogens
• Bifidobacterium
• Peptococcus
• Methanogenic bacteria like Methanobacterium, methanosarcina
• Common aerobic bacteria includes;
• Zeoglea remigera
• Noacrdia
• Flavobacterium
• Achromobacter
• Nitrosomonas
2. Algae:
•Some algae found in sewage includes Chlorella phormidum, Ulothrix etc
•Algae are used in trickling filter in sewage treatment plant
3. Fungi:
•Fungi like Fusarium and Sporotricum are found in sewage which play important role in trickling filter.
4. Virus:
•Some viruses causing human disease such as Poliovirus, Rotavirus, Hepatitis A and E etc are found in sewage
which get access through stool of patients.
5. Protozoa:
•Some protozoa that cause disease of intestinal tract enter into sewage together with stool of patient.
•Examples: Entamoeba histolytica, Giardia, Balantidium coli etc are pathogenic protozoa
•Few protozoa such as Vorticella and Opercularia are found in trickling filter.