Q.Name the states involved in Ganga action plan.
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🔒 Start your 14-day free trial to unlock the full solution →Concept understanding — Biochemical Oxygen Demand
Imagine you have a glass of clean drinking water and a glass of water from a muddy, smelly pond. If you left both out in the sun for a few days, the pond water would turn foul and cloudy much faster. Why? Because the pond water is full of organic waste — dead leaves, sewage, or leftover food — that tiny bacteria in the water start to eat. As these bacteria feed, they breathe oxygen, just like we do. The more waste there is, the more bacteria grow, and the more oxygen they consume from the water.
That consumption of oxygen by bacteria is the core idea behind Biochemical Oxygen Demand, or BOD.
What BOD actually measures
BOD is a measure of the amount of dissolved oxygen that microorganisms (mainly bacteria) need to break down organic matter present in a water sample over a specific time, usually 5 days, at a fixed temperature (20°C). Think of it as the "appetite" of the water for oxygen. If the water has a high BOD, it means there is a lot of organic waste for bacteria to decompose, so they will use up a large amount of oxygen.
The NCERT textbook for Class 12 Biology (Chapter 16: Environmental Issues) states it clearly: "Biochemical Oxygen Demand (BOD) refers to the amount of the oxygen that would be consumed if all the organic matter in one liter of water were oxidised by bacteria." The key point is that BOD is not a measure of the waste itself, but of the oxygen required to clean that waste biologically.
Why BOD matters in the real world
BOD is the single most important indicator of organic pollution in rivers, lakes, and wastewater. Here is why it matters:
- It tells you how polluted the water is. Clean river water typically has a low BOD (say, under 5 mg/L). Sewage water, on the other hand, has a very high BOD (often 200–600 mg/L). The higher the BOD, the dirtier the water.
- It predicts the health of aquatic life. Fish and other aquatic animals need dissolved oxygen to survive. When BOD is very high, bacteria use up so much oxygen that there is little left for fish. This can lead to "dead zones" where nothing can live.
- It guides wastewater treatment. Before sewage or industrial effluent is released into a river, treatment plants must reduce its BOD to a safe level. The government sets legal limits for BOD in treated water. If a factory releases water with high BOD, it is breaking the law. …
The Ganga Action Plan (GAP) was launched in 1985 to improve the water quality of the river Ganga, which was receiving a huge untreated sewage and industrial-effluent load from towns along its course, raising its biochemical oxygen demand and depleting dissolved oxygen.
The NCERT chapter text itself does not name any specific states or towns -- it only says the Ganga Action Plan was initiated "to save these major rivers of our country from pollution." Beyond the book, the real-world Ganga Action Plan's first phase (1985) is well known to have concentrated on three states:
- Uttar Pradesh — cities such as Kanpur and Varanasi
- Bihar — cities such as Patna
- West Bengal — cities around Kolkata, on the Hooghly distributary …
The Ganga Action Plan (1985) initially covered Uttar Pradesh, Bihar, and West Bengal — the three states through which the Ganga flows in its most polluted stretches — before expanding in later phases.
The Ganga Action Plan was launched in 1985 as India's first major river-cleaning initiative, born out of urgent concern over the deteriorating condition of the Ganga. The river, sacred to millions and a lifeline for nearly half a billion people, had become severely polluted by untreated sewage, industrial effluents, and ritual waste. The plan aimed to intercept, divert, and treat this pollution before it reached the river.
In its first phase (GAP-I), the programme focused on the three states where pollution was most acute and where the Ganga carried the heaviest load of urban and industrial waste:
- Uttar Pradesh — home to major pilgrimage and industrial cities like Varanasi, Kanpur, and Allahabad (now Prayagraj), which discharged enormous quantities of untreated sewage and tannery effluents directly into the river.
- Bihar — covering stretches around Patna and other urban centres where domestic and industrial waste added to the pollution burden.
- West Bengal — including Kolkata and surrounding areas, where the Hooghly (a distributary of the Ganga) faced severe contamination from both municipal sewage and industrial discharge. …
A different angle: trace the Ganga's course on a map and mark where the major polluting cities sit, instead of recalling a list of state names.
Following the river downstream from its Himalayan origin: it enters the plains and passes major urban centres — Kanpur and Varanasi (Uttar Pradesh), then Patna (Bihar), then on to Kolkata on the Hooghly distributary (West Bengal) before reaching the Bay of Bengal. …
- AP EAPCET 2024Set ap-2024-05-16-AN1 markMCQQ.Match the following. List-1: A. Eutrophication, B. Biomagnification, C. BOD, D. Cultural eutrophication. List-2: I. Demand of oxygen, II. Natural ageing of lake by nutrient enrichment, III. Increasing pollutant concentration at successive trophic levels in aquatic food chain, IV. Human activity accelerate ageing process of lake (A) A-II, B-IV, C-I, D-III (B) A-III, B-II, C-IV, D-I (C) A-III, B-IV, C-I, D-II (D) A-II, B-III, C-I, D-IV
›Reveal solutionSolution
Matches ecological/pollution terms to their definitions: A-II, B-III, C-I, D-IV.
Concept and Intuition
Eutrophication is the natural process by which a water body accumulates nutrients over time and gradually 'ages,' eventually filling in with vegetation. When human inputs (sewage, fertilizer runoff) accelerate this same nutrient enrichment, it is termed cultural eutrophication. Biomagnification is a distinct phenomenon in food chains, where persistent pollutants (like DDT) increase in concentration at each successive trophic level because they are not readily excreted. Biochemical/Biological Oxygen Demand (BOD) measures the amount of dissolved oxygen consumed by microorganisms decomposing organic matter in water — a standard indicator of organic pollution load.
Step-by-Step Solution
- A. Eutrophication → natural ageing of a lake by nutrient enrichment → II.
- B. Biomagnification → increasing pollutant concentration at successive trophic levels → III.
- C. BOD → demand of oxygen (for microbial decomposition) → I. …
- AP EAPCET 2021Set ap-2021-09-03-AN1 markMCQQ.Study the following statements and select the incorrect ones?(i) Physical removal of large and small particles through filtration and sedimentation is called primary sewage treatment(ii) Secondary sewage treatment is mainly a mechanical process(iii) Activated sludge sediment in a sewage treatment plant is a rich source of aerobic bacteria(iv) Biogas, commonly called as gobar gas, is pure methane (A)(i) &(ii) only (B)(ii) &(iv) only (C)(ii) &(iii) only (D)(iii) &(iv) only
›Reveal solutionSolution
This tests the stages of sewage treatment and the composition of biogas. The incorrect statements are (ii) (secondary treatment is biological, not mechanical) and (iv) (biogas is a mixture, not pure methane) — option (B).
Concept and Intuition
Sewage treatment happens in stages: primary treatment is purely physical — removing large and small suspended solids by filtration and sedimentation (floating debris skimmed off, grit settled out). Secondary (biological) treatment then passes this effluent through aeration tanks where it is vigorously agitated and aerobic microbes are allowed to grow, forming flocs called activated sludge; these microbes consume the remaining organic matter, drastically reducing the BOD (biochemical oxygen demand) — this is a biological, not mechanical, process. A small part of the activated sludge is pumped into anaerobic sludge digesters, where anaerobic bacteria digest the sludge, producing a mixture of gases (biogas/gobar gas) — mainly methane, but also CO₂, hydrogen sulphide, and other gases, so it is never "pure" methane.
Step-by-Step Solution
- Evaluate (i): Primary sewage treatment = physical removal of solids via filtration and sedimentation. This is correct as stated.
- Evaluate (ii): Secondary treatment involves passing effluent through aeration tanks with active growth of aerobic microbes (biological process) — calling it "mainly a mechanical process" is incorrect. …
- AP EAPCET 2021Set ap-2021-09-07-FN1 markMCQQ.Assertion (A): Bioremediation is the use of microbes to remove toxic substances. Reason (R): Certain microbes are present naturally in the sewage which help in sewage treatment (A) A is correct but R is wrong (B) A is wrong but R is correct (C) Both A and R are correct (D) Both A and R are not correct
›Reveal solutionSolution
Bioremediation uses microbes to remove toxic substances, and sewage-treatment plants rely on naturally present microbes to do exactly this — both statements are true.
Concept and Intuition
Bioremediation is the general term for using biological agents — most commonly bacteria and other microbes — to degrade, detoxify, or remove pollutants from a contaminated environment (soil, water, or wastewater). Municipal sewage treatment is one of the most familiar large-scale applications of this principle: sewage naturally contains a diverse microbial community, and treatment plants harness these microbes (in aeration tanks, activated sludge, etc.) to break down organic matter, reducing pollution load before the water is released.
Step-by-Step Solution
- Assertion: "Bioremediation is the use of microbes to remove toxic substances" — this is the standard textbook definition of bioremediation, and it is correct.
- Reason: "Certain microbes are present naturally in the sewage which help in sewage treatment" — this is also a correct, well-established fact; primary and secondary sewage treatment stages depend on these naturally occurring/aerobic heterotrophic microbes. …
- AP EAPCET 2021Set ap-2021-09-07-FN1 markMCQQ.The purpose of biological treatment of waste water is to ____ (A) Reduce BOD (B) Increase BOD (C) Reduce sedimentation (D) Increase sedimentation
›Reveal solutionSolution
Biological (secondary) treatment of wastewater uses microbes to consume organic pollutants, thereby reducing BOD — a measure of how polluted the water is.
Concept and Intuition
Biochemical Oxygen Demand (BOD) is the amount of dissolved oxygen that microorganisms would need to break down the organic matter present in a water sample over a given time. Untreated sewage has a high BOD, since it's rich in biodegradable organic material — releasing such water into a river would cause aquatic microbes to consume most of the dissolved oxygen, suffocating fish and other aquatic life. Biological (secondary) treatment deliberately encourages microbial breakdown of this organic matter under controlled conditions (e.g., in an aeration tank with activated sludge), so that most of the biodegradable material is removed before the water is discharged, resulting in a much lower BOD.
Step-by-Step Solution
- Recall the definition of BOD — a direct measure of the organic pollution load of water/wastewater. …
- AP EAPCET 2021Set ap-2021-09-06-FN1 markMCQQ.Activated sludge have the ability to settle quickly so that it can _________ (A) Be rapidly pumped back from sedimentation to aeration tank (B) Absorb pathogenic bacteria present in waste water, while sinking to the bottom of the settling tank (C) Be discarded and anaerobically digested (D) Absorb colloidal organic matter
›Reveal solutionSolution
The rapid-settling property of activated sludge allows a portion of it to be recycled from the settling tank back into the aeration tank as a microbial inoculum, keeping the treatment process running efficiently.
Concept and Intuition
Secondary (biological) sewage treatment uses aeration tanks where effluent is vigorously agitated and aerated, allowing aerobic microbes to grow and form flocs while consuming organic matter (measured as BOD reduction). This microbe-rich floc mass is called activated sludge. After aeration, the mixture is passed to a settling (sedimentation) tank where the flocs, being of a size and density that sink quickly, settle out. A part of this settled sludge is pumped back into the aeration tank to maintain a continuous, healthy population of decomposer microbes for treating fresh incoming sewage, while the excess settled sludge is passed on to anaerobic sludge digesters.
Step-by-Step Solution
- Recall the flow of the activated sludge process: aeration tank → settling/sedimentation tank → sludge disposal + effluent.
- Recognise that rapid settling of the sludge flocs is what enables efficient separation in the sedimentation tank. …
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