Class 7 Science Chapter 13 Notes Wastewater Story
→ Aeration : It is the process in which air is pumped into clarified water to help bacteria grow.
→ Aerobic bacteria : Bacteria that require oxygen to live and grow are called aerobic bacteria.
→ Anaerobic bacteria : Bacteria that survive without oxygen are called anaerobic bacteria.
→ Bioga : It is a gaseous fuel produced by the fermentation of manure, plant or crop waste under aerobic conditions which is used to generate electricity from the waste matter.
→ Contaminants : The harmful substances which are dissolved and suspended as impurities in water.
→ Sanitation : The proper disposal of sewage and garbage from the houses or nearby areas is called sanitation.
→ Sewag : Waste water generated by homes, offices, hospitals, industries and other areas is called a sewage.
→ Sewer : A network of big and small pipes used to carry waste water to treatment plant is called sewer.
→ Sewerage : It is the drainage system of sewer.
→ Sludge : It is the residential, semi solid material that is produced as a by product during sewage treatment
of industrial or municipal waste water.
→ Wastewater is generated from various sources :
- Domestic wastewater which is generated at home comprises urine, faeces, detergent, dirt and food wastes.
- Industrial wastewater contains poisonous chemicals and metals.
- Wastewater generated from hospitals contain several types of disease causing germs and dangerous radioactive materials.
- Agricultural wastewater comprises rainwater that picks up fertilisers and pesticides from the land while flowing over it.
- Rainwater may pick up various contaminants such as soil particles, animal waste, oil, grease, organic compounds, etc. while running over the surface of the ground. It may also carry human faeces if people defecate in the open.
→ Sewage contain’s many impurities called contaminants. Many disease causing microorganisms such as Entamoeba histolytica which causes dysentery, is present in sewage.
→ Sewage goes through a system of pipes, called sewers, which are linked to each other to form a network called sewerage system.
→ Sewage from houses, usually, flows through cast iron or polyvinyl chloride (PVC) pipes, which may be 8 to 10 cm in diameter.
→ Manholes are openings on the road surface that are covered with heavy cemented or metallic lids, which help to reach the underground sewerage for cleaning and maintenance.
→ Sewers are of two types; Sanitary sewers and storm water sewers. Sewers which carry only domestic sewage are called sanitary sewers and the sewers which help in carrying run-offs from rain and melted snow are called storm water sewers.
→ Sanitary sewers can overflow during floods and there is also a risk of flood water contaminating drinking water supplies. This results in the outbreak of cholera epidemics after flood.
→ In cities, disposal of domestic sewage and storm sewage is separated by different sewer systems.
→ Treatment of wastewater is done in Wastewater Treatment Plant (WWTP). It is also called Sewage Treatment Plant (STP).
→ The first step of wastewater treatment is to pass the wastewater through bar screens, which are screens of vertical bars that removes large solid materials such as cans, plastic bags, etc.
→ The stream of sewage which enters the treatment plant is called influent and the water which comes out of the treatment plant is called effluent.
- Water is then allowed to go into a grit and sand removal tank where the speed of the incoming wastewater is decreased so that solid heavy objects like sand, grit and stones settle down and are removed.
- Sedimentation tanks in the sewage treatment plants are also called as clarifiers as they clear all the floatable materials like oil and grease and solids like faeces from the sewage treatment plant.
- In a digester the sludge is decomposed by anaerobic bacteria to release biogas. Anaerobic bacteria do not require oxygen for their survival.
- Biogas is a methane rich gas which is also called as gobar gas. It is made up of methane (50-70% ), carbon dioxide ( 30-40% ) along with very little amount of nitrogen, hydrogen sulphide and hydrogen. It is used directly as fuel and does not pollute the air. It is a storable form of energy.
- In an aeration tank of a sewage treatment plant, aerobic bacteria is allowed to grow by pumping air and consume organic matter, soaps, detergents, etc. Aerobic bacteria cannot grow in the absence of oxygen.
- Aeration also helps in the circulation of oxygen through the clarified water, thereby, helping in removal of foul odour from it.
- The treated water is, sometimes, treated with disinfectants like chlorine and ozone, before discharging into water bodies.
- Water supply, sanitation and health are closely related. Without adequate quantities of water for personal hygiene, skin and eye infections (trachoma) spread easily.
→ In some places in our country, there are open drains to dispose off the sewage which may easily get blocked by plastic bags and can overflow. This may result in breeding of mosquitoes, flies, germs and problem of foul smell in these drains.
→ An economical alternative for sewage disposal is onsite sewage disposal system.
→ Septic tanks are large tanks where the sewage is allowed to decompose with the help of anaerobic bacteria. It acts as sedimentation-cum-digestion tank.
→ In septic tanks, anaerobic digestion of the settled sludge occurs in its bottom zone and the remaining liquid is passed through a soak pit or filter bed for treatment.
→ Septic tanks can be constructed in areas where the water tabla is very low and rainwater from the surface does not interfere with their functioning.
→ Composting toilet is a dry toilet that uses a predominantly aerobic processing system that treats excreta, typically with no water or small volumes of flush water through composting or managed aerobic decomposition.
→ Microbes feed on organic matter present in the sewage and break it down into simpler substances. This is called decomposition.
→ We all can play a role in making our environment healthy and clean by adopting good sanitation practices.