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Waste Water Story
"Jal Hai, To Kal Hai" your parents or teacher must have often advised you not to waste water, because there is shortage of water. Less than of all the water on earth is fresh water that we can actually use. We use this small amount of water for drinking, transportation, in industry and many other purposes.
1.0Introduction
The dirty water which is produced in kitchens, bathrooms, while washing cars or your bicycles and industrial wastes is called wastewater. Wastewater is used water. What happens to this dirty waste water in your homes? Where, do you think that rain water runs, from the streets? What happens to waste chemicals and other materials from factories? Are there any harmful effects of the waste water? In this chapter, we will get to know about the waste water.
Clean water
Clean water is a basic need of all of us. It is needed for several purposes - for drinking, cooking food, bathing, washing clothes, growing crops and even for industries. Unfortunately, clean water is not available for use, to many people. As a result, people suffer from a number of water-related diseases like typhoid, cholera and dysentery. Even deaths may take place. Now not only the clean water is available in short supply, there is an acute shortage of water as such.
2.0Sewage
Sewage is the waste water from homes domestic liquid waste as well as from industries, offices, hospitals and other places. All the wastewater that is released from various source forms the sewage which contains suspended impurities. These impurities are called contaminants. The contaminants can be classified as follows:
Sewage, thus, is a complex mixture containing suspended solids, organic and inorganic impurities, nutrients and disease - causing organism.
Water assists in many important function our bodies perform every day. Since it flows through our organs and cells, water needs to be clean and free of disease, metals and human and animal faeces.
3.0Understanding our sewer system
Each time we wash something or flush our toilets, water containing paper, cloth, scrap, detergent, oil, grease, food scrap, faeces, etc., goes down the drain. This water gets accumulated and forms sewage. In large cities, this is also known as municipal wastewater. Let us take a look at the journey it makes before flowing into a water body.
The Sewer System
The sewer system is a channel of pipelines which carries out sewage from our houses. The sewage leaves our houses through drain pipes and flows to the sewer mains of the city. Waste flows easily through sewers due to a slight slope given to the drainage system. Most sewer pipes are underground. So, what does one do if there is a leak or blockage in any of these pipes? For this purpose, we have manholes. A manhole is a hole, usually with a cover, through which a person may enter a sewer or drain to fix the faulty pipes.
What happens to the sewage after it flows through sewer mains? Where does it go? The sewer mains flow into progressively larger pipes until they reach the wastewater treatment plant.
In October 2007, Sulabh designed a system of cheap toilets that recycles human wastes into biogas and fertilisers. For this, the founder of sulabh, Dr. Bindeshwar Pathak, has even been awarded to Stockholm Water Prize of 2009. In most cases, the local municipal bodies have laid a network of drainage pipes throughout a city. Through this network, the sewage is released into nearby waterbodies i.e. lakes or rivers.
In big cities or towns, however, the waste sewage water is first treated in waste water treatment plants. Then, it is released in nearby rivers or lakes. People living downstream often drink and use this water.
The sewer system
Home Drain pipes Sewer system Larger pipes Waste water treatment plant Water bodies.
4.0Treatment of polluted water
Perform the following activity. It will help you understand the processes that take place at the wastewater treatment plant.
Divide yourself into groups to perform the activity. Record observations at each stage. Fill a large glass jar 3/4 full of water. Add some dirty organic matter such as grass pieces or orange peels, a small amount of detergent and a few drops of an ink or any colour. Cap the jar, shake it well and let the mixture stand in the sun for two days.
- After two days, shake the mixture and pour a small sample into test tube. Label this test tube "Before treatment; Sample 1". How does it smell?
- Use an aerator from an aquarium to bubble air through the sample in the glass jar. Allow several hours for aeration; leave the aerator attached overnight. If you do not have an aerator, use a mechanical stirrer or a mixer. You may have to stir it several times.
- The next day when aeration is complete, pour another sample into a second test tube. Label it as "After aeration; Sample 2".
- Fold a piece of filter paper to form a cone. Wet the paper with tap water and then insert the cone in a funnel. Mount the funnel on a support (as you have learnt in Class VI).
- Place layers of sand, fine gravel and finally medium gravel in the funnel figure. (An actual filtration plant does not use filter paper, but the sand filter is several metres deep).
- Pour the remaining aerated liquid through the filter into the beakers. Do not allow the liquid to spill over the filter. If the filtered liquid is not clear, filter it a few times till you get clear water.
- Pour a sample of the filtered water into a third test tube labelled
- Pour another sample of the filtered water into a fourth test tube. Add a small piece of a chlorine tablet. Mix well until the water is clear. Label the test tube "Chlorinated; Sample 4".
- Observe carefully the samples in all the test tubes. Do not taste! Just smell them
5.0Wastewater treatment plant (WWTP)
A wastewater treatment plant is a facility that treats wastewater from industrial source. There are basically three processes involved in treating wastewater: primary, secondary, and tertiary.
Primary process:
This is a mechanical process which involves screening and settling of large particles. First the sewage is passed through screens of vertical bars to remove larger impurities such as metal cans, plastic bags, cloth pieces, etc. The wastewater is then passed through a grit and sand removal tank called the grit chamber.
Vertical Bars
Grit Chamber
Sedimentation Tank
The speed of the incoming wastewater is reduced so that sand, grit, pebbles, etc. settle down. The water is then passed through huge sedimentation tanks. Here solid waste such as faeces is allowed to settle down and the light floatable waste such as soaps, oils, plastics and greases rise. The material that settles at the bottom is referred to as sludge and the material that rises to the top as scum.
Scum: Light floatable waste that rises to the top during wastewater treatment is called the scum. The water that comes out of the sedimentation tanks is called clarified water.
Effluent: Discharge of liquid waste from an industry is called effluents.
Secondary process:
This is a biological process in which the organic matter in the sludge is broken down with the help of bacteria. This process is called digestion and as a result of this process biogas is produced. This biogas can be used either as a fuel or to produce electricity. The treatment at this stage can be speeded up by allowing water to flow into large aeration tanks, where air is blown into the sewage.
Tertiary process:
This is basically a chemical process in which chemicals are used to remove phosphorus and nitrogen from the water. Addition of chlorine and exposure to ultraviolet light kills any remaining bacteria and disinfects the water. The water is then discharged into water bodies.
6.0Alternative arrangement for sewage disposal
Low cost onsite sewage disposal systems have been developed to take care of places where there is no sewage system like in rural areas or in case of isolated buildings.
These systems include septic tanks and chemical toilets. A septic tank consists of a concrete or metal tank with an outlet submerged in the ground. Domestic sewage enters the tank through another inlet pipe. The solids settle down in the tank and the liquid flows through the outlet pipe into the soil.
Biogas plant:
Another method of waste disposal which is prevalent especially in village and small towns in India is setting up of biogas plants. In this method, human and animal excreta flow through covered drains into biogas plants. Microorganisms break down the materials present in the waste and produce biogas. This biogas is then used to produce electricity.
Vermi-composting Toilets:
Recently vermi-composting toilets have been developed in India as an alternative method for proper disposal of waste. It is based on an innovative design in which earthworms are used to convert human excreta into compost. There is minimal use of water and is a safe and hygienic way of processing human waste.
7.0Become an active citizen
(i) Wastes should be disposed of properly and not thrown away anywhere. (ii) Proper toilet facilities should be provided to rural people. (iii) Chemical wastes from the factories should be properly treated before being released into water. (iv) Sewage from cities should not be discharged directly into rivers. It must be treated and made harmless before release. (v) Ensure that there are no leaking sewage pipes. (vi) Ensure that there is no stagnant water in ponds and lakes. The clarity of water in a stream, river or ocean is a key determinant in fostering a healthy and balanced aquatic ecosystem. The clearer the water, the greater the ability of light to penetrate to aquatic plants which generate the oxygen needed of aquatic life.
Better house keeping practices
- Chemicals like paints, insecticides and medicines should not be thrown in the drains. These things may kill microbes that help to purify water.
- Used food remains, tea leaves, cotton sanitary towels should not be thrown in the drains. These waste choke the drains and do not allow free flow of oxygen. This slows down the degradation process. Such wastes should be thrown in the dustbin.
- Cooking oil and fats should not be thrown down the drain. These items on hardening block the pipes. Oil and fats should be thrown in the dustbin.
- Reduce the quantity of waste production.
8.0Sanitation at public places
In our country fairs are organised periodically. A large number of people participate in them. In the same way railway stations, bus depots, airports, hospitals are very busy places. Thousands of people visit them daily. Large amount of waste is generate here. It must be disposed of properly otherwise epidemics could break out. The government has laid down certain standards of sanitation but, unfortunately, they are not strictly enforced. However, all of us can contribute in maintaining sanitation at public places. We should not scatter litter anywhere. If there is no dustbin in sight, we should carry the litter home and throw it in the dustbin.
9.0Building Concepts
What is the reason behind increasing scarcity of freshwater?
- The increasing scarcity of freshwater is due to population growth, pollution, industrial development, mismanagement and other factors.
What is the relation between sanitation and diseases?
- Poor sanitation and contaminated drinking water is the cause of a large number of diseases. A vast number of our people are still without sewerage facilities. A very large fraction of our people defecates in the open, on dry riverbeds, on railway tracks, near fields and many a time directly in water. Untreated human excreta is a health hazard. It may cause water pollution and soil pollution. Both the surface water and groundwater get polluted. Groundwater is a source of water for wells, tubewells, springs and many rivers. Thus, it becomes the most common route for water borne diseases. They include cholera, typhoid, polio, meningitis, hepatitis and dysentery.
10.0Basic terminology
- Sewage - Sewage in the waste water from homes. (domestic liquid waste) as well as from industry, offices, etc.
- Contaminants - Generally suspended impurities are called contaminants.
- Manholes - A manhole is a hole in sewer system usually with a cover, through which a person enter to fire faulty pipes.
- WWTP - Waste water treatment plant.
- Aeration - Aeration in process of adding air into waste wate to allow aerobic biodegradation of organic materials.
- Sludge - Impurities that settles at the bottom.
- Scum - Impurities that rises to the tap is called scum.
Alternatives of Sewerage System (Septic tanks, Chemical toilets