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Wastewater is water contaminated by human use such as industrial discharge, washing of clothes, agricultural as well as commercial activities. The sources of contamination degrade the quality of water leading to the contamination of water. It also depends on various products or sources such as domestic and municipal water, sewage and industrial waste of chimneys. Wastewater contains biological, chemical, and physical pollutants. This wastewater can then be purified by various methods carried out in power plants.
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Key Terms: Wastewater, waste, water, contamination, pollutants, industrial discharge
What is Wastewater?
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All effluent from hospitals, households, commercial institutions and organisations is referred to as wastewater. It also includes horticultural, agricultural, and urban runoff. Effluent can be understood as sewage or liquid waste that is discharged in the water bodies either from direct sources or from treatment plants.
- Contaminants are things that contaminate a substance such as food or water.
- Organic impurities can include the substances that can pollute the abiotic substances such as soil, water, etc.
- The organic impurities that pollute the water are together known as sewage.
- Inorganic impurities include nitrates, phosphates, and metals.
- Bacteria are tiny organisms that are tiny lifeforms that can only be seen with a microscope.
- Sewage is liquid waste that contains a complex mixture of suspended solids, nutrients, organic and inorganic impurities, and other microbes.
- Saprophytic Bacteria feed on dead and decaying plants and animals that are rich in organic matter.
Wastewater
Effect of Contamination of Water
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Water Contamination results in various harmful effects such as:
- Loss of Aquatic Organisms: Contaminated water harms aquatic organisms. Runoff of harmful contaminants such as pesticides and discharges in the waterways can be fatal to aquatic life and lead to the death of prawns, fishes, etc.
- Decrease in Biochemical Oxygen Demand (BOD): The harmful contaminants in the water can use up the natural oxygen that is present in the waterbody. Excess of nutrients can also cause algal bloom and when these algae die and decomposes, more oxygen is used up. The decrease in the level of oxygen can lead to difficulty in breathing for the aquatic organisms.
- Loss of Local Invertebrate Species: The small invertebrates act as food for the fishes. Their death leads to the starvation of fishes and other aquatic organisms who depend on them for food. They then start to migrate to other water bodies that expose them to harm and great threat.
- Decreased Quality of Water: Contaminated water decreases the clarity of water which makes the water murky. Hence, aquatic organisms are not able to see clearly and detect predators.
- Reduce Reproductive Ability of Aquatic Organisms: Contaminated water is harmful to aquatic organisms as they lose their reproductive ability, cause disorders in their Central Nervous System (CNS), and lowers their immunity.
Wastewater Management
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The treatment of wastewater includes several steps that are used to purify the contaminated water by removing its contaminants to make it usable. The steps for the wastewater treatment are as follows:
- Wastewater Collection
- Screening
- Primary Treatment
- Secondary Treatment
- Final Treatment
Wastewater Treatment
Wastewater Collection
The first step to manage wastewater is to collect water in a storing tank where it further goes through many filtration steps.
Screening
Screening is the first step for water treatment. In this step, large objects from the wastewater are removed and then are added into the grit and sand removal tank where further treatment takes place.
Primary Treatment
In the primary treatment, all the organic wastes that are present in water are removed. This process is performed by pouring wastewater into a big tank and then processing the same. The solid matter then settles down at the bottom of the tank and it is known as the sludge.
The sludge is then decomposed by bacteria and biogas is released by the process. Biogas can be further used to generate electricity and it can also be used as a fuel.
Secondary Treatment
After the primary treatment, water goes to the aeration tank where the air is tapped in the water in order to increase the growth of aerobic bacteria. These bacteria then break down the small sludge particles that are not broken down in the primary treatment. These broken slugs are referred to as activated sludge.
Final Treatment
The activated sludge is then passed through a bed of sand drying machines. The water gets filtered and thus the sludge dries up in this step. The water is then made to flow over a wall where additional elements, if any, are eliminated. The filtered water is then released into the river.
Sewage Systems
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From each house, sewage is collected through the network of pipes and drainage known as sewers that takes them to wastewater treatment plants from where it is released in the water bodies.
- Better housekeeping practices: Cooked fats and oils should not be thrown down the drain as they clog the pipes. Remains of solid food, used tea leaves, sanitary towels, pieces of cotton, etc. should also not be pushed down the drain as they restrict the free flow of oxygen and thereby hampers the process of degradation.
- Vermi-processing toilet: In the process, waste sewage slurry that is collected from the disposal system is treated with earthworms, tiger worms, and wigglers. The faecal matter and other organic waste are decomposed. The process is really simple, hygienic and consumes less water. It leads to no odour or flies problem.
- Sanitation: It can mainly be understood as the provision of services and facilities that deals with the safe disposal of urine and human faeces. Poor sanitation can lead to multiple health hazards and diseases.
- Septic tanks: A buried water tight container is known as a septic tank. It is usually formed of concrete polythene where sewage is collected and then allowed to decompose by the activity of bacteria before draining by soaking the same.
Sewerage System
Things to Remember
- Wastewater is the water contaminated by humans by agricultural activities, industrial discharge, washing of clothes, and commercial activities.
- Effluent is the sewage or liquid waste discharged in the water bodies.
- Water contamination results in loss of aquatic organisms, decreased biochemical oxygen demand, and decreased quality of water.
- Wastewater can be treated by its proper management in a wastewater treatment plant.
- The steps involved in wastewater treatment are wastewater collection, screening, primary treatment, secondary treatment, and final processing.
Sample Questions
Ques. How is water pollution classified depending on the source? (3 marks)
Ans. As per the source, the types of water pollution are:
- Surface Water Pollution: The type of pollution in lakes, rivers, and oceans is known as surface water pollution. The water sources here are contaminated through various means of industrial waste, the release of waste or sewage, etc.
- Groundwater Pollution: Groundwater can be contaminated by the use of pesticides and insecticides. This is directly related to soil pollution.
- Marine Pollution: The pollution caused as a result of the discharge of industrial waste and sewage into the ocean is known as marine pollution. Plastic debris in the ocean can poison any creature that consumes it.
Ques. How can water pollution be controlled? (3 marks)
Ans. The various ways to control water pollution are:
- Industrial Wastewater Treatment: Industrial wastewater is a major cause of water contamination. The treatment of this waste to reduce the harmful chemicals present in it will control water pollution.
- Municipal Wastewater Treatment: Instead of directly discharging sewage waste in the water bodies, its treatment in a separate sewage treatment plant can help reduce water pollution.
- Agriculture Wastewater Treatment: Underground water pollution can be controlled by reducing the use of pesticides and insecticides in agriculture. This is because these chemicals can cause various health issues.
Ques. What is the composition of sewage? (5 marks)
Ans. Sewage is composed of the following components:
- Organic impurities are present in the sewage as animal wastes, human faeces, oil, vegetable and fruit wastes, herbicides, pesticides, etc.
- Inorganic impurities are present in the sewage as phosphates, nitrates, and metals.
- Sewage has phosphorus and nitrogen nutrients.
- The bacteria include the ones that cause water borne diseases such as typhoid and cholera.
- Other microbes in sewage include protozoa that cause a waterborne disease known as dysentery
Ques. What is a wastewater treatment plant? (3 marks)
Ans. A wastewater treatment plant is a place where sewage or wastewater from houses or other buildings is processed. The treatment of wastewater involves the following steps:
- Physical Process (Screening)
- Biological Processes
- Chemical Processes
Ques. Write a short note on sewage system. (3 marks)
Ans. The pipes carrying away sewage or wastewater from buildings are buried underground. An underground pipe that carries waste matter and dirty drainage water is known as sewer. Sewerage can be understood as an interconnected system of pipes or sewers located underground. It is responsible for carrying the sewage from where it is produced to the sewage treatment plants where its processing takes place.
Ques. How does contaminated water affects the environment? (3 marks)
Ans. The environment is affected by the contaminated water in the following ways:
- It can be fatal for fishes and other aquatic organisms.
- There is a decrease in the biochemical oxygen demand.
- The reproductive ability of the aquatic organisms is hampered.
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