UPSC CSE Prelims
Clean and Green Technologies Previous Year Questions (PYQs)
Practice solved questions for Clean and Green Technologies with detailed step-by-step solutions, key insights, and trend analysis for UPSC CSE PRELIMS.
Solved Previous Year Questions
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In rural road construction, the use of which of the following is preferred for ensuring environmental sustainability or to reduce carbon footprint?
- Copper slag
- Cold mix asphalt technology
- Geotextiles
- Hot mix asphalt technology
- Portlant cement
Select the correct answer using the code given below:
Detailed Explanation:
Answer: Option 1 — 1, 2 and 3 only
For ensuring environmental sustainability and reducing carbon footprint in rural road construction, copper slag (a by-product reducing natural resource demand), cold mix asphalt (lower temperature processing with reduced emissions), and geotextiles (synthetic materials minimizing excavation and resource use) are preferred. Hot mix asphalt requires high energy consumption, and Portland cement production is carbon-intensive, making them less environmentally sustainable choices.
✅ Statement 1 – Correct: Copper slag, a copper refining by-product, can replace sand in concrete, reducing sand mining and environmental impact.
✅ Statement 2 – Correct: Cold mix asphalt technology operates at lower temperatures, consuming less energy and emitting fewer greenhouse gases compared to hot mix.
✅ Statement 3 – Correct: Geotextiles provide soil stabilization and drainage while reducing the need for excessive excavation and natural resource consumption.
❌ Statement 4 – Incorrect: Hot mix asphalt technology requires high temperatures and thus higher energy consumption, making it less environmentally sustainable.
❌ Statement 5 – Incorrect: Portland cement production is highly energy-intensive and emits significant CO₂, contributing substantially to carbon footprint.
📝 Short Notes: Sustainable Road Construction Materials
| Material/Technology | Environmental Benefits | Carbon Footprint Impact |
|---|---|---|
| Copper Slag | By-product utilization; reduces sand mining; waste recycling | Low - diverts industrial waste |
| Cold Mix Asphalt | Lower production temperature (60-100°C vs 150-180°C); allows recycled materials; can be produced on-site | Reduced by 30-50% compared to hot mix |
| Geotextiles | Reduces excavation depth; improves soil stability; extends road life; reduces gravel/stone requirement | Low - reduces material transport and extraction |
| Hot Mix Asphalt | Good performance but high energy demand | High - requires 150-180°C processing |
| Portland Cement | Limited - energy-intensive production | Very High - 0.8-0.9 kg CO₂ per kg cement |
- Green Road Construction: Focus on using industrial by-products, recycled materials, and low-energy technologies
- Rural Road Context: PMGSY (Pradhan Mantri Gram Sadak Yojana) encourages use of sustainable materials and local resources
- Geotextiles Applications: Separation, filtration, drainage, reinforcement, and erosion control in road construction
- Fly Ash & Slag: Other industrial by-products increasingly used as sustainable alternatives in road construction
With reference to bio-toilets used by the Indian Railways, consider the following statements:
- The decomposition of human waste in the bio-toilets is initiated by a fungal inoculum.
- Ammonia and water vapour are the only end products in this decomposition which are released into the atmosphere.
Which of the statements given above is/are correct?
Detailed Explanation:
❌ Statement 1 – Incorrect: Bio-toilets used by Indian Railways employ anaerobic bacteria (not fungi) as the inoculum to decompose human waste in an oxygen-free environment.
❌ Statement 2 – Incorrect: The decomposition produces methane gas, carbon dioxide, treated water (after chlorination), and minimal sludge – not just ammonia and water vapour.
Biomass gasification is considered to be one of the sustainable solutions to the power crisis in India. In this context, which of the following statements is/are correct?
- Coconut shells, groundnut shells and rice husk can be used in biomass gasification.
- The combustible gases generated from biomass gasification consist of hydrogen and carbon dioxide only.
- The combustible gases generated from biomass gasification can be used for direct heat generation but not in internal combustion engines.
Detailed Explanation:
✅ Statement 1 – Correct: Coconut shells, groundnut shells, and rice husk are excellent agricultural residues and biomass feedstock for gasification due to their high carbon content and low moisture.
❌ Statement 2 – Incorrect: The syngas (synthesis gas) from biomass gasification primarily contains carbon monoxide (CO), hydrogen (H₂), methane (CH₄), and carbon dioxide (CO₂), not just hydrogen and carbon dioxide.
❌ Statement 3 – Incorrect: Syngas from biomass gasification can be used for both direct heat generation and in internal combustion engines after proper cleaning and cooling to remove tar and particulates.
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