Wastewater Story: Class 7 Science NCERT Chapter 18

Key Features of NCERT Material for Class 7 Science Chapter 18 – Wastewater Story

In the last chapter 17, you all learned about Forests. In chapter 18 of class 7 science NCERT textbook: Wastewater story, you will learn about the story of water and its wastage.

Quick revision notes

Water is a mixture of life. We as a whole use water and in that cycle of utilizing, we make it filthy. The water rich in  foam, blended in with oil and different toxins that go down the channels from sinks, showers, latrines, laundries is grimy. It is called wastewater.

We use water each day for drinking, washing, washing garments, preparing food, washing utensils, flushing latrines, wiping the floors, and so on. We can’t think about our life without water. We use heaps of water day by day which is given to the waste system consistently.

Water, Our Lifeline

Water is required by all types of life. Clean water is an essential need of individuals. Tragically, clean water isn’t accessible to a huge section of human populaces.

The water which is unsuitable for human utilization turns into the wellspring of many water-borne diseases which eventually lead to loss ( of human life. It is assessed that one billion individuals don’t get protected drinking water. Thus, understanding the direness we celebrate 22nd March as World Water Day to bring mindfulness among individuals for safe water, fit for human utilization.

In this way, the water is cleaned by eliminating toxins before it enters a waterbody or is reused. This cycle of wastewater treatment is generally known as sewage treatment which happens in a few stages as talked about later.

On World Water Day, for example 22 March 2005, the General Assembly of the United Nations announced the period 2005-2015 as the International Decade for activity on Water forever. All endeavors made during this decade mean to lessen significantly the quantity of individuals who don’t approach safe drinking water.


It is wastewater delivered by homes, enterprises, agricultural fields and other human exercises. It likewise incorporates water that has run down the road during a tempest or weighty downpour and it is fluid waste. The majority of its water has broken up and suspended impurities called contaminants.

Organization of Sewage

The accompanying segments make the sewage:

  • The natural impurities present in sewage are human excrement, creature squanders (like creature fertilizer), urea (as pee), oil, leafy foods squanders, pesticides, herbicides, and so on.
  • The inorganic impurities present in sewage are nitrates, phosphates and metals.
  • The supplements present in sewage are nitrogen and phosphorus.
  • The microorganisms present in sewage incorporate those microscopic organisms which cause water-borne diseases, for example, cholera and typhoid.
  • Different organisms present in sewage are Protozoa which cause a water-borne malady called looseness of the bowels.

Water Freshens Up: An Eventful Journey

In a house (an open structure) for the most part, there are two sets of channels, for example one set of channels carries clean drinking water into the house and the other set of funnels removes wastewater (sewage) from houses. For legitimate disinfection, a well-maintained sewage system is required.

Sewerage System

The funnels which divert wastewater or sewage from houses and different structures are covered under the ground. An underground funnel which diverts messy seepage water and waste issues is called sewer. The arrangement of seepage at a spot by laying sewers under the ground is called sewerage. As a matter of fact, sewerage is an underground system of interconnected funnels considered sewers that conveys the sewage from where it is delivered to the sewage treatment plants, where it is handled.


A manhole is a shrouded vertical gap in the ground, pavement or street, over the underground sewer pipeline through which a laborer can go down up to the sewer pipes for examination, cleaning, and so forth. Manholes are given at each 50-60 m separation in the principle sewer pipeline. Manholes are likewise given at the intersection of at least two sewers and at focuses where there is an adjustment toward the sewer line.

Treatment of Polluted Water

Play out the accompanying action. It will assist you with understanding the cycles that occur at the wastewater treatment plant.

Wastewater Treatment Plant (WWTP)

A spot where wastewater or sewage from houses and different structures is brought for handling is called a wastewater treatment plant.

Treatment of wastewater includes physical, organic and substance measures relying upon the nature of contaminants.

  1. Physical Process (Screening)

The bar screens first eliminate the huge trash objects like clothes, sticks, jars, polybags, napkins, clean towels, and so forth., from the wastewater.

  Waste water story

In the wake of going through the bar screen, wastewater is taken to a tank called grit and sand removal tanks. In this, sand and grit settle down gradually at the base of the tank as water goes gradually through this tank. The settled sand and impurities are eliminated from the tanks every now and then.

  1. Natural Process

The first sedimentation tank is slanted towards the inside. Solid like defecation settles at the base and is called sludge which is eliminated by a scraper. Oils and grease coast at the outside of the water are eliminated by a skimmer. The biogas delivered (by anaerobic microorganisms) in the process can be utilized as fuel or can be utilized to create power. Here, water gets freed from rubbage, oil, grease, and so forth and we get clarified water which is sent to the air circulation tank now. In the air circulation tank, the watery waste as of now contains microscopic organisms (aerobic) in it. The packed air bubbles are gone through this loss to give 02 to the microorganisms to increment bacterial movement which eventually processes human waste, food waste, cleansers and other undesirable and hurtful issues despite everything staying in the wastewater abandoning genuinely unadulterated water.

  1. Substance Process

The water after air circulation tank is permitted to remain in a subsequent sedimentation tank. Here, the organisms present get settled at the base at the tank as enacted muck which is about 97% water. At this stage, water has low degree of natural suspended issue and doesn’t contain numerous unsafe things. It is ok for human utilization however is sanitized by chlorine or ozone before dispersing it.

Become an Active Citizen

Waste age is a characteristic piece of human movement however we can restrict the kind of waste and amount of waste delivered. Regularly we have been repulsed by a hostile smell. Seeing open channels is sickening. The circumstance declines in the rainy season when the channels begin flooding. We need to swim through the mud pools on the streets. Generally unhygienic and unsanitary conditions win. Flies, mosquitoes and different insects breed in it.

We ought to be an enlightened resident and approach the district or the gram panchayat. We ought to likewise demand that open channels ought to be secured. In the event that the sewage of a specific house makes the area messy. We should demand them to be more thoughtful about other’s wellbeing.

Note: We should plant Eucalyptus trees from the beginning sewage lakes. These trees assimilate all excess wastewater quickly and discharge unadulterated water fume into the climate.

Better House Keeping Practices

We should limit and oversee waste at our homes before its removal in the accompanying way:

  • Cooking oil and fats ought not be tossed down the channel. They can solidify and obstruct the channels. In an open channel, the fats obstruct the dirt pores lessening its adequacy in sifting water. Toss oil and fats in the dustbin.
  • Utilized tea leaves, strong food stays, delicate toys, cotton, sterile towels, and so on., ought to likewise be tossed in the dustbin. These wastes gag the channels. They don’t permit the free progression of oxygen. This hampers the corruption cycle.
  • The synthetic compounds like paints, solvents, insecticides, medications and engine oils ought not be tossed in channels as they murder accommodating microorganisms which digest the natural waste.

Sanitation and Disease

Contaminated water and helpless sanitation rehearses are the significant reasons for the quantity of irresistible sicknesses in our nation. Safe sewage removal offices are as yet not accessible at numerous urban areas and towns in India. Along these lines, individuals go to open places and poo. This causes the expansion in insect-vector populace which communicates sicknesses like cholera, typhoid, meningitis, and so on.

Untreated human excreta is a wellbeing danger which causes soil contamination and water contamination too. The waterway water and groundwater are wellsprings of water for drinking for some individuals. Thus, the contaminated water can spread numerous illnesses particularly water-borne.

Vermi-processing Toilets

In the vermi-processing latrines, human excreta is treated by worms in a pit. The night crawlers ordinarily gobble up all natural issues present in human discharge and transform it into fertilizer. These are tow water use latrines for the protected processing of humans.

Alternate Arrangement for Sewage Disposal

Ease outside the sewage removal system has been created to deal with places where there is no sewage system, for example country regions, disengaged structures. These are depicted beneath:

(I) Septic tanks:

Septic tank is an ease nearby sewage removal system. Septic tanks are appropriate where there is no sewerage made. These tanks need cleaning each four to a half year.

A septic tank for the most part comprises of a major, secured underground tank made of cement having a delta pipe toward one side and on outlet pipe at the opposite end. The latrine seat is associated with the channel funnel of the septic tank. The human excreta from the latrine seat goes into the septic tank through the bay channel. The strong piece of excreta continues gathering at the base of the septic tank as a muck though watery waste stays above it.

The anaerobic microorganisms breakdown the vast majority of the strong natural issue present in human excreta because of which the volume of strong waste is diminished excessively. The processed strong waste continues saving at the base of septic tank. The watery waste is likewise cleaned by anaerobic microorganisms. The overabundance water leaves the septic tank through the outlet pipe and get ingested in soil.

(ii) Composting pits:

These are self-supported human waste removal units which isn’t associated with a sewer line or a septic tank. A composting latrine separates and dries out human waste to compost.

(iii) Chemical latrines:

These latrines have restricted capacity limit with respect to human waste and should be discharged occasionally. These are the latrines which utilize artificially treated store found just beneath the latrine seats. The synthetic substances lessen the foul smell emerging from human discharge and do incomplete purification of human waste.

Sanitation at Public Places

In our nation, fairs are composed intermittently. An enormous number of individuals participate in them. Similarly, railroad stations, transport terminals, air terminals, medical clinics are extremely bustling spots. A huge number of individuals visit them every day which create enormous measure of waste. It must be discarded appropriately in any case pandemics could break out. The legislature has set out specific principles of sanitation yet unfortunately, they are not carefully authorized. We ought not dissipate litter anyplace. In the event that there is not a single dustbin to be found, we should convey the litter at home and toss it in the dustbin.


 We as a whole have a task to carry out in keeping our condition spotless and sound. We should understand our duty in keeping up the water sources in a sound state. Receiving great sanitation practices ought to be our lifestyle. As a problem solvers your individual activity will have an extraordinary effect. Impact others with your vitality thoughts and ideal, A great deal con be accomplished if individuals cooperate. There is extraordinary force in aggregate activity.

As a active resident, we have numerous obligations with respect to sanitation. These can be recorded as follows:

  • To guarantee that our environmental factors are perfect.
  • To guarantee that the sewerage system in our home is appropriately overseen.
  • In the event that any spillage or an open channel in the sewerage system is available, at that point it ought to be accounted for to the district or the gram panchayats to demand that the open channel must be secured appropriately and a few air and water-borne infections can be forestalled.


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