# Water and Soil Pollution for UPSC: BOD, Eutrophication, Treatment Technologies, Polluted River Stretches, Namami Gange and Groundwater Source: https://tracknation.in/story/water-and-soil-pollution-for-upsc-bod-eutrophication-treatment-technologies-polluted-river-stretches-namami-gange-and-groundwater (TrackNation — free UPSC notes with PYQs) > Water and soil pollution for UPSC: BOD and DO, eutrophication, biofilters, membrane bioreactors and activated carbon, sand mining, the CPCB's polluted river stretches (296 in 2025), Namami Gange, the 2025 groundwater assessment, the Water Act and the UNCCD. Includes practice questions and the real PYQs. ## How UPSC Tests Water and Soil Pollution 🎯 **Exam priority: Tier-2. Water questions ask technologies and regulation; soil questions are rare, so a short list of land-degradation facts is enough.** *UPSC asked: biofilters in aquaculture and what they do to ammonia (2023); membrane bioreactors as a wastewater technology (2024); the effects of sand mining on groundwater and salinity (2018); and why activated carbon is a cheap tool for removing heavy metals from effluent (2025 transcribed question). The same ideas return as Mains questions about river cleaning, groundwater stress and industrial effluent.* Keep three boxes in mind: **measure** (BOD, DO, the monitoring network), **treat** (the technologies) and **govern** (the Water Act, Namami Gange, groundwater assessment). ## BOD, DO, Eutrophication and Treatment Technologies ## Measuring and treating water pollution ### The key terms - **Dissolved oxygen (DO):** the oxygen in water that fish need. For outdoor bathing the primary criterion is DO of at least **5 mg/L**. - **Biochemical oxygen demand (BOD):** the oxygen microbes use to break down organic waste. A high BOD means heavy organic pollution and low DO. The bathing criterion is BOD of at most **3 mg/L**; pH should be 6.5 to 8.5. - **Eutrophication:** enrichment of a water body by nitrogen and phosphorus (fertiliser runoff, sewage) causes algal blooms that die, decay and use up the oxygen. ### Treatment technologies the exam has tested | **Technology** | **How it works** | | Biofilter (in aquaculture) | Holds bacteria that convert toxic ammonia in fish waste to nitrate (2023 PYQ); it removes waste, it does not add phosphorus | | Membrane bioreactor | Membrane filtration combined with activated-sludge biological treatment for wastewater (2024 PYQ) | | Activated carbon | Very large surface area that adsorbs heavy metals; can be made cheaply from carbon-rich waste, so it is attractive for effluent treatment (2025 question) | | Sewage treatment plant (STP) and common effluent treatment plant (CETP) | STPs treat domestic sewage; CETPs treat the combined effluent of small industries such as tanneries | **Sand mining** lowers the water table, lets pollutants reach groundwater and lets saline water move inland. It increases salinity; statements that it decreases salinity are wrong (2018 PYQ). ## Polluted River Stretches, Namami Gange and Groundwater ## Rivers and groundwater: what the data say ### Monitoring and polluted river stretches - The National Water Quality Monitoring Programme covers 28 States and 6 UTs: **2,260** river locations, 587 on lakes, 143 on ponds, 102 on tanks, 1,271 groundwater locations and 559 on other water bodies. The Ganga has real-time monitoring at **40 stations**. - A river location with BOD above **3 mg/L** is polluted; **two or more polluted locations in sequence make a Polluted River Stretch (PRS)**. Priority classes depend on the maximum BOD: I above 30 mg/L, II 20 to 30, III 10 to 20, IV 6 to 10 and V 3 to 6. - 351 stretches on 323 rivers in 31 States and UTs were identified in 2018. The 2025 assessment, based on 2022 and 2023 data, identified **296 PRS on 271 rivers** in 32 States and UTs, out of 623 rivers monitored; 149 of the 2018 stretches no longer qualified as polluted. - Industry: charters for the five major sectors (pulp and paper, distillery, sugar, textile, tannery) lifted compliance of grossly polluting industries in the Ganga basin to **82 per cent in 2023 from 39 per cent in 2017**; online continuous monitoring (OCEMS) is used to promote self-regulation. ### Namami Gange By the end of 2025 the National Mission for Clean Ganga had sanctioned **513 projects worth ₹42,019 crore** and completed 344. In the Ganga basin 216 sewerage projects have been sanctioned for **6,560 MLD** of treatment capacity and 5,220 km of sewers. The Ganga Pulse Public Portal shows real-time STP outlet quality (pH, BOD, COD, suspended solids) in the five main-stem States. ### Groundwater Resource Assessment 2025 | **Measure** | **Value** | | Annual recharge | 448.52 bcm | | Annual extractable resource | 407.75 bcm | | Annual extraction | 247.22 bcm (stage of extraction about 60.63 per cent) | | Assessment units | 6,762 | | Over-exploited (extraction above recharge) | 730 units (10.80 per cent) | | Critical (90 to 100 per cent) | 201 units (2.97 per cent) | | Semi-critical (70 to 90 per cent) | 758 units (11.21 per cent) | | Safe (below 70 per cent) | 4,946 units (73.14 per cent) | | Saline | 127 units (1.88 per cent) | Over-exploited and critical units exceed 25 per cent of units in Punjab, Rajasthan, Haryana, Delhi and Tamil Nadu. The **Atal Bhujal Yojana** (participatory groundwater management in seven States: Gujarat, Haryana, Karnataka, Madhya Pradesh, Maharashtra, Rajasthan and Uttar Pradesh, five years from 1 April 2020) has now ended its tenure. ## Water Act, Cess Act and the UNCCD ## The law, and a short note on soil and land - **Water (Prevention and Control of Pollution) Act, 1974 (amended 1988):** State Pollution Control Boards set and enforce effluent standards; the Central Board coordinates and acts for Union Territories. The 1988 amendment let the Boards *close* a defaulting plant instead of relying only on prosecution. - **Water Cess Act, 1977:** raises money for the Boards by charging designated industries and local bodies for water use; a polluter gets a **70 per cent rebate** on the cess after installing effluent treatment. - **Soil and land:** The **UN Convention to Combat Desertification (UNCCD, 1994)** is the first and only legally binding international agreement on drylands (arid, semi-arid and dry sub-humid areas), with a bottom-up approach that involves local communities. The Ministry of Environment, Forest and Climate Change is India's nodal ministry, and its Desertification Cell coordinates the work. ## How UPSC Could Ask This Next - **Technologies:** biofilters, membrane bioreactors, activated carbon, constructed wetlands and phytoremediation: what each removes. - **Measurement:** BOD versus DO, the bathing criteria, what makes a river stretch "polluted". - **Programmes:** Namami Gange, Atal Bhujal Yojana and the groundwater categories. - **Law:** what the 1988 amendment added and who sets effluent standards. ## Further Reading - NCERT Biology (Class 12) and Geography textbooks, the India State of Forest Report, the MoEFCC Annual Report, the Economic Survey and the official lists cited in this note — the primary sources behind every figure above. ## Test Yourself: Practice Questions and PYQs Twelve practice questions on water quality, treatment technologies, river and groundwater data and the Water Act, followed by the real UPSC Prelims questions. ## Practice Questions **Q1.** A river location is considered polluted if its Biochemical Oxygen Demand (BOD) exceeds - (a) 0.3 mg/L - (b) 30 mg/L - (c) 10 mg/L - (d) 3 mg/L **Answer: (d)** — BOD above 3 mg/L makes a location polluted. **Q2.** A Polluted River Stretch (PRS) is defined as - (a) a stretch with dissolved oxygen above 5 mg/L - (b) a river with more than one dam - (c) any single location with BOD above 3 mg/L - (d) two or more polluted locations in continuous sequence **Answer: (d)** — The definition needs two or more contiguous polluted locations. **Q3.** In the CPCB's 2025 assessment of polluted river stretches (based on 2022 and 2023 data), how many stretches were identified? - (a) 149 - (b) 311 - (c) 351 - (d) 296 **Answer: (d)** — 296 PRS on 271 rivers; 351 was the 2018 figure and 311 the 2022 figure. **Q4.** In aquaculture, a biofilter holds bacteria that - (a) kill all bacteria in the tank - (b) add ammonia to the water - (c) convert toxic ammonia in fish waste into nitrate - (d) increase phosphorus for the fish **Answer: (c)** — UPSC's 2023 question: biofilters remove waste by nitrification. **Q5.** A membrane bioreactor is a technology used for - (a) wastewater treatment - (b) desalination of seawater only - (c) soil fertilisation - (d) generating hydroelectric power **Answer: (a)** — It combines membrane filtration with activated-sludge treatment. **Q6.** Which of the following are consequences of heavy sand mining in a river? 1. Lowering of the water table 2. Entry of pollutants into groundwater 3. Decrease in salinity of coastal groundwater 4. Movement of saline water inland - (a) 1, 2, 3 and 4 - (b) 1, 2 and 4 only - (c) 2, 3 and 4 only - (d) 1 and 3 only **Answer: (b)** — Sand mining increases salinity, so statement 3 is wrong. **Q7.** Why is activated carbon an attractive tool for treating industrial effluent? 1. It has a very large surface area that adsorbs heavy metals. 2. It can be made cheaply from carbon-rich waste. - (a) Both 1 and 2 - (b) 2 only - (c) Neither - (d) 1 only **Answer: (a)** — Both reasons are correct. **Q8.** Consider the following statements about the Groundwater Resource Assessment 2025: 1. About 60.63 per cent of the annual extractable resource is being extracted nationally. 2. 730 assessment units are over-exploited. 3. Over-exploited and critical units exceed 25 per cent of units in Punjab, Rajasthan, Haryana, Delhi and Tamil Nadu. Which of the statements given above are correct? - (a) 2 and 3 only - (b) 1 and 3 only - (c) 1, 2 and 3 - (d) 1 and 2 only **Answer: (c)** — All three match the assessment. **Q9.** A groundwater assessment unit is classified as 'Critical' when the stage of extraction is - (a) between 90 and 100 per cent - (b) between 70 and 90 per cent - (c) above 100 per cent - (d) below 70 per cent **Answer: (a)** — Over-exploited is above 100 per cent, semi-critical 70 to 90 and safe below 70. **Q10.** Which Act allowed the Pollution Control Boards to close a defaulting industrial plant after a 1988 amendment? - (a) Biological Diversity Act, 2002 - (b) Forest (Conservation) Act, 1980 - (c) Wildlife (Protection) Act, 1972 - (d) Water (Prevention and Control of Pollution) Act, 1974 **Answer: (d)** — The 1988 amendment to the Water Act added the power of closure. **Q11.** Under the Water (Prevention and Control of Pollution) Cess Act, 1977, a polluter that installs effluent treatment equipment gets a rebate of - (a) 10 per cent of the cess - (b) 70 per cent of the cess - (c) no rebate - (d) 100 per cent of the cess **Answer: (b)** — The Act gives a 70 per cent rebate to encourage investment in treatment. **Q12.** The UN Convention to Combat Desertification (UNCCD) of 1994 is - (a) a legally binding convention on drylands that takes a bottom-up approach involving local communities - (b) an agreement on ozone-depleting substances - (c) a voluntary declaration without parties - (d) a convention on migratory birds **Answer: (a)** — UNCCD is the legally binding convention for drylands. ### UPSC Previous Year Questions (PYQs) *Real UPSC Prelims questions, checked against the official paper and answer key.* **Q1.** (2023) With reference to the role of biofilters in Recirculating Aquaculture System, consider the following statements : 1. Biofilters provide waste treatment by removing uneaten fish feed. 2. Biofilters convert ammonia present in fish waste to nitrate. 3. Biofilters increase phosphorus as nutrient for fish in water. How many of the statements given above are correct? - (a) Only one - (b) All three - (c) None - (d) Only two **Answer: (d)** — Biofilters hold bacteria that convert toxic ammonia in fish waste into nitrate and remove waste; they do not increase phosphorus for the fish. Statements 1 and 2 are right. **Q2.** (2024) “Membrane Bioreactors” are often discussed in the context of: - (a) Wastewater treatment technologies - (b) Assisted reproductive technologies - (c) Vaccine production technologies - (d) Drug delivery nanotechnologies **Answer: (a)** — Membrane bioreactors combine membrane filtration with activated-sludge treatment, a wastewater-treatment technology. **Q3.** (2018) Which of the following is/are the possible consequence/s of heavy sand mining in river beds? 1. Decreased salinity in the river 2. Pollution of groundwater 3. Lowering of the water-table Select the correct answer using the code given below: - (a) 1 and 3 only - (b) 2 and 3 only - (c) 1, 2 and 3 - (d) 1 only **Answer: (b)** — Heavy sand mining lowers the water table, lets pollutants reach groundwater and lets saline water move inland. It increases salinity rather than decreasing it, so 2 and 3. **Q4.** (2025) Consider the following statements : Statement I : Activated carbon is a good and an attractive tool to remove pollutants from effluent streams and to remediate contaminants from various industries. Statement II : Activated carbon exhibits a large surface area and a strong potential for adsorbing heavy metals. Statement III : Activated carbon can be easily synthesized from environmental wastes with high carbon content. Which one of the following is correct in respect of the above statements? - (a) Neither Statement II nor Statement III is correct - (b) Both Statement II and Statement III are correct but only one of them explains Statement I - (c) Both Statement II and Statement III are correct and both of them explain Statement I - (d) Only one of the Statements II and III is correct and that explains Statement I **Answer: (c)** — Activated carbon has a large surface area for adsorbing heavy metals and can be made cheaply from carbon-rich waste, which is why it is an attractive effluent-treatment tool. II and III both explain I. ### Mains Practice Questions Use these to frame full-length answers. You don't have to answer one exactly — they show the angles UPSC tests, so let them guide which points you cover. - Explain the terms BOD and DO. How do they relate to eutrophication, and why is BOD the criterion for identifying polluted river stretches in India? - Despite substantial investments, Namami Gange has had a mixed record in cleaning the Ganga. Evaluate the progress using the sewage treatment capacity sanctioned and completed, and suggest the missing pieces. - Groundwater over-extraction is concentrated in a few States. Using the 2025 assessment, explain the causes and a policy mix to correct it. - Compare the roles of the Water Act, 1974 and the Water Cess Act, 1977. How effective is an incentive such as the 70 per cent rebate? - Discuss the role of treatment technologies (biofilters, membrane bioreactors, activated carbon, constructed wetlands) in reducing industrial and domestic water pollution. ### UPSC Mains — Previous Years’ Questions on this topic (last 10 years) These are the **actual GS Mains questions** UPSC has asked on this theme — real proof of how, and when, it is tested. Try to write a full answer to each. - 2025 (GS-III): Seawater intrusion in the coastal aquifers is a major concern in India. What are the causes of seawater intrusion and the remedial measures to combat this hazard? - 2024 (GS-III): Industrial pollution of river water is a significant environmental issue in India. Discuss the various mitigation measures to deal with this problem and also the government's initiatives in this regard. - 2023 (GS-III): What is oil pollution? What are its impacts on the marine ecosystem? In what way is oil pollution particularly harmful for a country like India? - 2017 (GS-III): Not many years ago, river linking was a concept but it is becoming a reality in the country. Discuss the advantages of river linking and its possible impact on the environment. (Answer in 150 words)