Waste Water Management Notes

Wastewater

The water which gets contaminated after various works; like washing, bathing, mopping, etc. is called wastewater.

World Water Day: 22nd March

International Decade for Action on Water for Life (2005 – 2015): It was declared by the General Assembly of the United Nations. Its main goal was to reduce the number of people who do not have access to safe drinking water; by half.

Sewage Treatment: The process of removing impurities from waste water before it can be reused or sent to the water bodies is called sewage treatment or cleaning of water.

Sewage: The liquid waste which has water as its largest component; along with various types of impurities; is called sewage.

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Composition of Sewage

Type of impurities	Examples
Organic impurities	Human faeces, animal waste, oil, urea (urine), pesticides, herbicides, fruits and vegetables
Inorganic impurities	Nitrates, phosphates, metals
Nutrients	Phosphorus, nitrogen
Bacteria	Various types; such as those causing cholera, typhoid, etc.
Other microbes	Various types; such as those causing diarrhea, jaundice, etc.

Sewers: The pipes which carry wastewater.

Sewerage: The network of sewers.

Manhole: These are the holes made in sewers at frequent intervals, so that timely inspections and cleaning of sewers can be done through them. The manhole is covered with a hard lid so that people and traffic can easily move over it.

Review Questions:

What is sewer?

Answer: The pipe which carries the wastewater is called sewer.

What is sewerage?

Answer: The network of sewers is called sewerage.

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Wastewater Treatment Plant or Sewage Treatment Plant:

These are large plants where wastewater is cleaned before being sent to the nearest water bodies or being reused. The sewage treatment involves physical, chemical and biological processes to remove impurities from the wastewater.

Physical Process:

1. Filtration: The wastewater is passed through bar screen. Large objects; like rags, sticks, plastic bags, cans, etc. are removed in this process.

2. Grit and Sand Removal: The wastewater is slowly passed through the sedimentation tank. Grit, sand and pebbles settle down at the bottom.

3. Sedimentation: Water is then sent to the sedimentation tank. Solids; like faeces settle at the bottom. Floatable impurities; like oil and grease float on the surface. A scraper removes the faeces from the water. The impurity thus collected is called sludge; which is sent to the sludge tank. The sludge can be used to produce biogas or to produce manure. A skimmer removes the floatable impurities. Now, the water is called clarified water.

Biological Process

4. Aeration: Air is pumped into clarified water so that bacteria can proliferate. Bacteria consume the human waste. It leaves food waste, soap and other unwanted materials in the water. The microbes settle down at the bottom after several hours. Water is then removed from the top. This water is fit for irrigation and can be used for that purpose.

Chemical Process

5. Chlorination: Water purified through aeration is not fit for human consumption. It needs to be treated with chlorine. For this, bleaching powder is added to the water. The chlorine kills whatever germs may be left in the water. After chlorination, the water is fit for drinking.

Review Questions

Which process during the wastewater treatment results in proliferation of bacteria?

Answer: Aeration

Which process during the wastewater treatment kills the germs?

Answer: Chlorination

Better Housekeeping Practices to Maintain Sanitation:

• Do not throw cooking oil and fat in the drain. This can block the drain. The fat and oil clogs the pores in the soil; in open drains. This reduces the filtering capacity of soil.
• Do not throw chemicals; like paint, insecticides, medicines, etc. into the drain. They kill the bacteria which otherwise help in cleaning the water.
• Do not throw used tea leaves, solid food, soft toys or napkins in the drain. They can clog the drain and do not allow oxygen to enter the sewage water. Oxygen is important for the natural process of decomposition.

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Sanitation and Disease

Maintaining overall cleanliness in the home and in surroundings is called sanitation. Sanitation is important for the health of a person and that of the community.

Many people have the habit of defecating in the open. Uncovered human excreta attract flies and other insects. These insects carry the germs of many dangerous diseases; like cholera, typhoid and jaundice. With constant public awareness campaign, the practice of open defecation can be stopped.

Poor sanitary conditions also contaminate the groundwater because contaminants percolate down the ground.

Stagnant water is a perfect breeding ground for mosquitoes. Mosquitoes are the carriers of several diseases; like malaria, dengue, chikungunya and filaria.

Alternative Arrangements for Sewage Disposal

• In the absence of a sewerage system, arrangements for onsite sewage disposal can be made. For example; septic tanks are built in which human excreta are collected. In due course of time, the human excreta get decomposed into compost.
• Composting pits can be made to dump waste and to make manure from them. Sewage can be collected into biogas plants to produce useful biogas.
• Chemical toilets are new discoveries. They do not require much water for the disposal of human excreta and are environment friendly. Such toilets are ideal for the trains.

Sanitation at Public Places

Maintaining sanitation at public places is also important. In a heavily populated country; like India; any public place is always teeming with people. More footfall at public places results in more filth. Sanitation workers often work continuously to maintain cleanliness at public places. But it is our responsibility also to maintain sanitation at public places. We should follow some simple rules to help the sanitation workers. For example; always throw the trash in a dustbin and avoid littering. Don’t spit at public places and use the dustbin or special bins marked for the purpose.

Revision Notes on Wastewater Story

Water Pollution

When the water present on earth in the oceans, seas, rivers, lakes, ponds and under the ground gets contaminated, it is termed as water pollution. The contamination of water results in a change in its physical, biological and chemical properties and hence makes it unsafe for drinking or usage of other purposes. The substances that cause water pollution are called Water Pollutants. The pollution of water can lead to serious effects such as diseases, an effect on the ecosystem of a region, and loss of aquatic life.

Major Water Pollutants

·         Sewage: a massive amount of wastewater or sewage is dumped into water bodies such as rivers and seas which pollutes their freshwater and makes it inappropriate for any kind of consumption due to the rise of several bacteria and other microorganisms. It not only affects the aquatic life of the water body but also leads to severe diseases like cholera, diarrhoea and typhoid.

·         Industrial Chemical Wastes: Harmful chemicals such as lead and mercury are often dumped by industries into the water bodies directly which contaminate their water.

·         Agricultural Effluents: Fertilizers, pesticides, insecticides and farm wastes are often washed off by the rain to the water bodies and contaminate the water.

·         Oil Spills: Oil spills often occur due to accidents and leakages of oil in the sea which leads to loss of aquatic life.

·         Thermal Wastes: Thermal industries often spill warm water in the water bodies which decreases its oxygen content. It also leads to a rise in temperature of water which is not suitable for aquatic animals.

·         Suspended Solids: They come from soil erosion, untreated sewage and mining. These suspended pollutants block the sunlight from reaching the aquatic plants and animals.

Organism	Diseases	Remarks
Ascaris sp.	Nematode worms	Danger to man from polluted water and dried sludge used as a fertilizer.
Bacillus anthracis	Anthrax	Found in waste water spores are resistant to treatment.
Brucella sp.	Brucellosis, Malta fever in man, contagious abortion in sheep, goat and cattle.	Transmitted by infected milk by contact, by waste water.
Entameoba histolytcca	Amoebic dysentery	Spread by contaminated water.
Leptospira sp.	Leptospirosis (Well's Diseases)	Caused by sewer rats.
Mycabact, tuberculi	Tuberclosis	Isolated from waste water
Salmonella paratyphi	Paratyphoid fever	Common in waste water
Salmonella typhi	Typhoid fever	Common in waste water
Salmonella sp.	Food poisoning	Common in waste water
Shigella sp.	Bacillary dysentery	Polluted water
Vibrio cholarae	Cholera	Polluted water
Virus	Poliomyelitus hepatitis	Waste water treatment plants
E. coil	Diarrhoea	Polluted water

What is wastewater?

The water that has been used and is not fit for usage again is called Wastewater. It is dirty water from the laundry, toilets, sinks and drains.

Water - Our Lifeline

Figure 1: Usage of clean water

·         We all need clean water however, not all can access the same.

·         Hence, it is necessary not only to preserve water but clean the used water before dumping it into the seas or any other water body.

·         This is why the United Nations proclaimed the period between 2005 and 2015 as the International decade for action on ‘water for life’.

What do you mean by cleaning of water?

It is a process in which the pollutants from the water are removed before the water reaches a water body or before it is used again. This process is also called Sewage Treatment.

What is sewage?

·         Wastewater from houses, offices, Industries, hospitals and other sources is called Sewage.

·         Rainwater that flows into the drains during heavy rainfalls is also sewage because it contains pollutants that it washes off from the roads.

·         Any liquid waste can be called sewage.

·         Sewage water contains impurities mixed into it as well as some suspended pollutants.

·         These impurities present in the sewage are called Contaminants as they contaminate the water. 

Figure 2: Sewage is a mixture of impurities

Water freshens up - An Eventful Journey

·         Sewers - Large and small pipes that are installed in buildings to carry sewage water are sewers.

·         Sewerage - A network or transport system consisting of sewers is called Sewerage.

·         It carries sewage water from the point where it is produced to the point where it is disposed (treatment plant).

·         It consists of manholes that are located at every 50 to 60 metres.

·         The manholes are installed at a point where two or more sewers intersect or change their directions.

·         Every locality has as a system that allows removal of waste from the houses and industries.

Figure 3: Sewerage

Wastewater Treatment Plant (WWTP)

Wastewater includes biological, physical and chemical matter and hence involves biological, physical and chemical processes of removal of the contaminants.

The physical and biological process of treatment of water:

1. Separation of Large Objects from Sewage Water

The wastewater is first passed through bar screens which remove big objects from the water like plastic bottles, napkins, rags, cans and sticks.

Figure 4: Bar Screens

2. Separation of Sand and Dirt

The wastewater is then sent to a grit and sand removal tank. The speed of the water is decreased at this step. This allows the sand, dirt and pebbles to settle down.

3. Removal of Solids

·         Now the water cycles in a tank called Clarifier which is sloped in the centre. This lets the solids like faeces to settle at the bottom. This is called Sludge.

·         The sludge is then separated from the water with the help of a Scrapper.

·         Substances like oil and grease are removed with the help of a Skimmer as they float above the water. In this step clarified water is obtained.

·         The sludge so obtained is passed into a tank where anaerobic bacteria can decompose it and produce biogas. The biogas is then used as a fuel.

Figure 5: Sand and Girt Removal Tank

4. Suspended Sludge Removal

·         The clarified water also needs to be cleaned further. Hence, it is moved to an aerator that pumps air into it.

·         This allows aerobic bacteria to grow in this water.

·         The aerobic bacteria consume organic waste, soaps, food waste and other elements that remain in the clarified water.

·         This water is allowed to settle for several hours and then these waste materials settle down in the tank. This is called Activated Sludge.

·         The water is removed from the top of this sludge with the help of machines or sand drying beds. The sludge is then dried and can be used as manure.

Figure 6: Aerator

This treated water contains fewer amounts of impurities and suspended matter. This water is safe to dump into a water body or under the ground. Hence, it is then discharged into a sea, river or underground. Nature further cleans it up.

Chemical Treatment of Wastewater:

·         Sometimes harmful chemicals can be present in the water even after treating them physically and biologically.

·         These chemicals are therefore removed by using disinfectants such as chlorine and Ozone.

·         Often chlorine gas or ozone gas is introduced in this water which purifies it chemically.

Figure 7: WWTP

Eucalyptus Plant and Cleaning of Water

Eucalyptus plants can absorb the water at a faster rate and then they release pure water vapour. In this way, they act as a natural water purifier. Hence, it is advised to plant Eucalyptus trees along the sewage ponds.

Figure 8: Eucalyptus Plant

Why should we adopt better housekeeping practices and become an active citizen?

·         We should try to reduce the waste that produced in our households so that there is not much pressure on WWTP. It is often difficult to clean tons of wastewater.

·         The sewage water can cause several problems such as harmful diseases, unhygienic and unsanitary conditions in the locality.

·         Hence, we can be more considerate about producing a limited amount of waste and we can accomplish this by adopting better housekeeping practices.

·         Also, we can become an active citizen by making sure that there are no open drains or sewers in our locality. If we find any we should immediately report the same to the municipality.

What better housekeeping practices we can adopt?

A good way to minimise the sewage water is to check what is going in our drains. If we dispose of our waste properly we may be able to reduce the sewage. Here are some housekeeping practices that we should adopt:

·         We should through all the oil and fats in dustbin rather than throwing them of the dream. Oil and fats harden and block the drains. Moreover, it is difficult to separate them from the water.

·         We should not throw chemicals in the drains like insecticides, pesticides or medicines. They can kill the microbes in the water that help in its purification.

·         We should not throw things in the drain that can block them like tea leaves, food remains, cotton, soft toys etc. We should always through them in the dustbin.

Figure 9: Treating Water at home

Sanitation and Disease

·         Sanitation refers to the health conditions of people related to the disposal of sewage, human excreta and provision of clean drinking water.

·         Poor sanitation and polluted drinking water can lead to many diseases.

·         Hence, a sanitation system aims to provide a clean environment for us so that we can stay away from diseases.

·         Improper sanitation can give rise to different diseases that arise from contaminated water such as typhoid, dysentery, hepatitis, polio, cholera and meningitis.

·         The human excreta is a health hazard and can lead to soil and water pollution. It can pollute the surface water and groundwater. Hence, people should never defecate in open areas.

Alternative Arrangement for Sewage Disposal

·         As an alternative for sewage disposal on-site sewage is being used nowadays, for example, septic tanks, compost pit toilets and chemical toilets.

·         The onsite sewage treatments use natural procedures to treat and dispose of the wastewater or sewage.

·         This system is suitable in places where there is no central wastewater collection system.

o    Septic Tanks – A septic tank is often installed under the ground in houses or buildings such as hospitals. It allows decomposition of sewage from home through the action of anaerobic bacteria.

o    Chemical Toilets – A chemical toilet has a separate compartment that treats human waste with chemicals and decreases their odour.

o    Composting Toilets – A composting toilet treats human waste with biological processes. The aerobic bacteria are present in a storage tank that act upon the waste and turn it into compost.

Many organizations have also installed on-site hygienic waste disposal technology in which the human excreta directly flows into a biogas plant and is then used as an energy resource.

Sanitation at Public Places

·         There are numerous places in our country which are very busy such as airports, railway stations and bus depots.

·         Many times large gatherings such as fairs and festivals are also organized where a large number of people visits.

·         This results in the generation of large amounts of waste and if the waste is not treated properly it can lead to several diseases and even an epidemic.

·         Hence we should all become aware and contribute to maintaining sanitation not only in our homes but also at public places.

·         If we adopt certain practices at public places we can help in maintaining their sanitation, for instance:

o    We should not throw garbage in public places and always use the dustbins.

o    We should not spit around in a public place.

Link for waste water management : https://www.youtube.com/watch?v=b0G8R2YfW5k

Class 7 - Biology - Wastewater Story

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Question 1:

Fill in the blanks:

(a) Cleaning of water is a process of removing ____________.

(b) Wastewater released by houses is called ____________.

(c) Dried ____________ is used as manure.

(d) Drains get blocked by ____________ and ____________.

Answer:

(a) Cleaning of water is a process of removing pollutant.

(b) Wastewater released by houses is called sewage.

(c) Dried sludge is used as manure.

(d) Drains get blocked by oils and fats.

Question 2:

What is sewage? Explain why it is harmful to discharge untreated sewage into rivers or seas.

Answer:

Sewage is a liquid waste which has water as its largest component along with various types of impurities like waste water from houses, offices, factories, hospitals etc., is called sewage.

It has a complex mixture containing suspended solids, organic and inorganic impurities, nutrients, saprotrophic and disease causing bacteria and other microbes.

Discharging untreated sewage into rivers or seas will pollute the water resources.

Contaminated water is dangerous for aquatic plants and animals. It also spread many diseases like cholera, typhoid, polio, meningitis, malaria, dengue etc.

Question 3:

Why should oils and fats be not released in the drain? Explain.

Answer:

Oil and fats can clog the drains reducing its effectiveness in filtering water. In open drains, they block the pores in the soil and thus hamper the filtration by soil.

Hence, oil and fats should not be released into the drain.

Question 4:

Describe the steps involved in getting clarified water from wastewater.

Answer:

Treatment of wastewater involves physical, chemical, and biological processes, which remove physical, chemical and biological matter that contaminates the wastewater.

Following steps are involved:

o     Wastewater is passed through bar screens which remove large objects like rags, sticks, cans, plastic packets, napkins etc.

o    Water then goes through Grit and Sand removal tank, where sand, grit and pebbles settle down.

o    Water is then allowed to settle in a tank where solids like faeces (called sludge) settle at the bottom and are removed with a scraper. A skimmer removes the floatable solids like oil and grease. Water so cleared is called clarified water. Sludge is used to produce biogas.

o    Clarified water is then passed through an aerator tank where air is pumped into the water. It helps aerobic bacteria to grow which decompose organic matter like human waste.

o    After several hours, the suspended microbes settle at the bottom of the tank as activated sludge. The water is then removed from the top. The dried activated sludge is used as manure.

o    Water is removed from the top and is stored in a tank. The treated water has low level of organic material and suspended matter. It is discharged into a sea, a river or into the ground. Sometimes it is disinfected through chemicals like Chlorine and ozone and then distributed to towns.

Question 5:

What is sludge? Explain how it is treated.

Answer:

Sludge is human waste (like faeces) in waste water left during sewage treatment. Since it is organic waste, it is used to produce bio gas and manure.

Sludge is collected by a scrapper. It is transferred to a separate tank where it is decomposed by the anaerobic bacteria.

The biogas produced in the process can be used as fuel. After the aerator tank, microbes and human waste settle down and form activated sludge.

The activated sludge is about 97% water. The water is removed by sand drying beds or machines. Dried sludge is used as manure, returning organic matter and nutrients to the soil.

Question 6:

Untreated human excreta are a health hazard. Explain.

Answer:

Untreated human excreta contain many pathogens and disease causing microbe like cholera, diarrhea, typhoid, polio, meningitis, hepatitis etc.

The germs of these diseases can easily reach human population through air, water or insects and through contaminated food and water. Thus, untreated human excreta are a health hazard.

Question 7:

Name two chemicals used to disinfect water.

Answer:

Chemicals like chlorine (Chlorine dioxide) and ozone (in the pharmaceutical industry) are commonly used to disinfect water.

Question 8:

Explain the function of bar screens in a wastewater treatment plant.

Answer:

Bar screens are used to remove large objects like rags, sticks, cans, plastic packets napkins, etc. in wastewater treatment plant.

Question 9:

Explain the relationship between sanitation and disease.

Answer:

A large number of diseases is caused due to poor sanitation and contaminated drinking water.

Poor sanitation leads to growth of harmful microbes, flies and mosquitoes which are the source of spreading many diseases like cholera, typhoid, polio, meningitis, hepatitis and dysentery.

So, its better to have a good sanitation and proper hygiene.

Question 10:

Outline your role as an active citizen in relation to sanitation.

Answer:

Wastewater treatment plant requires costly infrastructure to build and to be maintained. So, we should be an active citizen and limit the type of waste. Try to follow the following:

o    Open drains be covered and keep our surroundings clean.

o    Chemicals like paints, insecticides, motor oil etc. should not be thrown in drain which may kill useful bacteria.

o    Used tealeaves, solid food remains, soft toys, cotton, sanitary towels, etc. should also be thrown in the dustbin.

o    Make people aware and encourage community practices to keep our environment clean.

o    Separate trash as recycled waste and non-recycled.

Question 11:

 Study the following statements about ozone:

(a) It is essential for breathing of living organisms. (b) It is used to disinfect water. (c) It absorbs ultraviolet rays. (d) Its proportion in air is about 3%.

Which of these statements are correct? (i) (a), (b) and (c) (ii) (b) and (c) (iii) (a) and (d) (iv) All four.

Answer:

(ii) (b) and (c).

Ozone is used to disinfect water and absorbs ultraviolet rays.

Rucha T Soni
(Science Teacher)