GATE — Environmental Science and Engineering (ES) · India · IITs and IISc on rotation (2026: IIT Guwahati)
Original practice questions written to the published syllabus · not past papersMunicipal, hazardous, biomedical, plastic and electronic waste: generation, collection, processing, energy recovery and landfills. Crop residue and manure handling are taught in the Agricultural Engineering subject waste-management-environmental-engg and livestock-farm waste in the Veterinary subject environmental-hygiene; this subject is the general waste-management science they draw on.
In the exams: GATE ES Section 7 (whole section); ICAR AICE subject 71 Unit 5 (whole unit); UGC NET Unit 7
GATE -- Environmental Science and Engineering (Section 7)
A whole section: generation and characterisation calculations (moisture, density, energy content), collection and transfer economics, composting C:N mixing, biogas yields, incineration energy and temperature criteria, landfill volume, liners, leachate and gas, hazardous waste characteristics, biomedical colour coding, e-waste and plastic rules.
How our questions for GATE spread across the units of Solid & Hazardous Waste Management. Difficulty: 18 easy, 13 medium, 3 hard.
| Composting and vermicomposting of organic waste | 4 | |
| MSW sources, generation rates and characteristics | 3 | |
| Collection, transfer and transport | 3 | |
| Material recovery and recycling | 3 | |
| Anaerobic digestion and biogas from organic waste | 3 | |
| Thermal processes: incineration, pyrolysis, gasification | 3 | |
| Sanitary landfill design, leachate and landfill gas | 3 | |
| Hazardous waste: characteristics, treatment and disposal | 3 | |
| Waste hierarchy and integrated solid waste management | 2 | |
| Biomedical waste management | 2 | |
| Plastic waste and extended producer responsibility | 2 | |
| Waste management rules and their national equivalents | 2 | |
| E-waste: hazards and resource recovery | 1 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
A 1.0 kg waste sample weighs 0.45 kg after oven drying. What is its moisture content on a wet basis?
C. 55%
(wet - dry)/wet = 0.55 = 55%. Dividing by dry mass gives the dry-basis value 122%.
Which resin identification code denotes PET?
B. 1
1 PET, 2 HDPE, 3 PVC, 4 LDPE, 5 PP, 6 PS, 7 other. PVC is 3, PP is 5 and 7 covers other plastics.
During thermophilic composting, temperatures typically reach:
B. About 55-65 degrees C
Heat from microbial activity kills pathogens and weed seeds.
A plant burns 1,000 t/d of waste with calorific value 8 MJ/kg at 22% electrical efficiency. What is its electrical output?
B. 20.4 MW
1,000,000 kg x 8 MJ x 0.22 / 86,400 s = 20.4 MW. Omitting efficiency gives the thermal input; dividing by 3,600 confuses hours and seconds.
A landfill receives 500 t/d of residual waste compacted to 0.85 t/m3, with cover soil adding 15% to volume. What volume is used each year?
A. 246,912 m3
500/0.85 x 1.15 = 676 m3/d; x 365 = 246,912. Omitting the cover allowance or multiplying by density gives the wrong volume.
Using first-order decay, Q = k L0 M e^(-kt), with k = 0.05/yr, L0 = 100 m3 CH4/t and M = 100,000 t placed in one year, what is methane generation 5 years later?
B. 389,400 m3/yr
0.05 x 100 x 100,000 x e^-0.25 = 389,400. Omitting k gives the remaining potential, not the annual rate.
A waste with pH 1.5 is hazardous under RCRA because it is:
B. Corrosive
Corrosivity: pH <= 2 or >= 12.5. Ignitability concerns flash point; reactivity concerns instability.
Microplastics are plastic particles smaller than:
B. 5 mm
They are found in soils, water, air and food. 5 micrometres and 5 cm are wrong size limits.
Global plastic production is now about:
D. 400 million t/yr
Most is packaging and short-lived products. Production is far larger than millions of tonnes and far smaller than tens of billions.
Which convention addresses persistent organic pollutants?
D. Stockholm Convention
Basel covers hazardous waste trade; Rotterdam prior informed consent for chemicals; Minamata mercury.
Ten here, 34 in the app. The Laisha app has every practice question we have written to GATE in this subject, marked as you go, with timed papers, a jump-to-unanswered list and a certificate when you pass at 70 per cent.
Free for ten days, then one subscription of US$10 a month. We would rather say so here than have you find it later.
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