Water is one of the basic necessities of life. We need water for all our household activities on a daily basis such as cooking, washing dishes or clothes, bathing or even using the toilet without water. The water becomes dirty after it is used for such activities. This used water which become dirty and unfit for further use is called wastewater.
The wastewater from your home contain used water made up of soap, food particles, strands of hair, traces of oil, dust, urine and human excreta. During monsoon, rainwater also gets into the drains and adds slit, pebbles, leaves and other plant material to the wastewater. The wastewater flowing through the drainage pipes is called sewage.
Sources of wastewater:
Treatment of sewage in cities and towns:
- Sewage water contains detergents, toxic chemicals food wastes, paper, human faeces, plastics, metal objects, microorganisms, blood, human/animal tissues, etc. These kinds of materials present in wastewater are called contaminants.
- In agricultural practices, pesticides and fertilizers are used, which gets mixed with fresh water during rains or flood, thereby contaminated the river and ponds.
- The wastewater from the industries may contain lubricant oil, paint, dye, chemicals and metals. These are also called Industrial effluents.
- Construction of buildings, mining leads to the generation of wastewater containing cement, paints, metals and chemicals.
- Abattoirs (slaughterhouses), animal farms and veterinary hospitals too contaminate water and contribute to sewage.
- One of the major sources of wastewater is domestic sewage from homes.
If sewage water is allowed to directly flow into the water bodies, it would pollute water. Such polluted water is not suitable for human consumption or for growing crops. It will also harm all kinds of plants and animals living in these water.
Thus, Wastewater must be cleaned before it is released into the water bodies. This is done in Sewage treatment plant or wastewater treatment plant. Treated wastewater can be used for various purposes.
Sewage treatment plant (Wastewater treatment plant):
Wastewater is treated using a series of physical, chemical and biological processes.
The pre-treatment process
involves the sewage being sent through grids or vertical bar that can remove large solid substances like metal cans, paper and plastic materials.
Primary treatment process:
In this process, the sewage flows through the grit chamber very slowly so that the sand, pebbles and soil settle down at the bottom.
It is a mechanical process; the sewage flows into the settling tank of sedimentation tank where the solid wastes like faeces are allowed to settle down.
The waste material that settle down at the bottom is called the sludge and the floatable material is called the scum.
The sludge at the bottom is removed with a scrapper every few days and treated further. The water then is left out is called the clarified water.
Secondary treatment process:
It is a biological process. This is done by transferring the clarified water into an aeration tank where air blowers bubble air, which helps the aerobic bacteria to grow and feed on the organic contaminants.
Microorganisms decompose most of the organic matter still present in the sewage.
The leftover liquid waste is allowed to remain in time so that microscopic organisms settle down at the bottom. This is called the activated sludge. This activated sludge is then left in sand dry beds.
Tertiary treatment process:
The leftover liquid waste is transferred to another large tank where the decomposed waste settles at the bottom. These tanks too are called sedimentation tanks.
At this stage, most of the solid substance from the water are removed.
The water is then shifted to a tank where it is treated with chlorine to kill all the microorganisms present in the wastewater and to remove the Phosphorus compounds and nitrogen compounds. Addition of chlorine to wastewater to kill germs is called chlorination. It is a chemical process.
The dirty water that was brought to the sewage treatment plant is now clean and can be used to cultivate crops, maintain large gardens, and manufacture goods in industries.
The water can also be discharged into oceans, rivers and lakes or used to recharge groundwater.
Effects of improper sewage management:
Methods of sludge management:
- Many places in our country have open drains in the streets. These serve as breeding places for mosquitoes, which cause diseases like malaria and Chikungunya.
- Untreated wastewater or sewage contains nutrients which are beneficial for the growth of algae. If this untreated wastewater is let off into the water bodies then it leads to an increase in algal growth called algal blooms. This causes depletion of oxygen in the water bodies making them unable to support aquatic life such a condition is called eutrophication.
- The overflowing drains can contaminate wells and streams too.
- The contamination can cause water- borne diseases such as Cholera, typhoid ,Hepatitis and dysentery.
- Sludge can be incinerated in sludge incinerators to convert it into ashes, which can be used in construction purposes or to supplement the nutrients in the soil.
- Dewatering of the sludge can be done by sludge- drying machines. The leftover solid waste is used in the manufacture of fertilizers.
- The gas produced by aerobic bacteria acting on the sludge in the aeration tank is used as biogas, which is a source of energy for cooking and electricity.
Alternative methods of wastewater management:
In many villages in our country, septic tank is used for treating household sewage.
A large concrete tank is built under the ground with inlet and outlet pipes attached to it. The inlet pipe carries the household sewage to the tank. Bacteria present in the tank decompose the solid waste. The excess water flows out of the tank through the outlet pipe into the soil.
It is suitable for places having sandy soil, as the outlet pipe gets blocked in clayey soil.
With the few modifications, a septic tank can be converted into an efficient biogas plant.
In such toilets, dilute Chemicals are used instead of water to act on human waste.
Control of sewage at homes:
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- Do not drain off cooking oil, paints and automobile oils. it leads to blockage.
- Chemical like paints, insecticides, medicines may kill decomposer microbes that help purify water, so, these must never be thrown down the drain.
- Do not drain the tea leaves, vegetable and animal food waste and egg shell. Solid waste clogs drains and make surrounding dirty.
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