60 solved GATE CE questions on Environmental Engineering, drawn from 5 exam years and grouped by year. Every question shows the official answer and a step-by-step solution.
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Identify the pollutant, its concentration, the flow, and the treatment objective before selecting a process. These selected foundations connect water quality parameters, treatment unit operations, air pollution, and solid waste management. The original exercises use idealized supplied data for learning; they are not instructions for designing treatment systems.
Our study notes and original examples support the PYQs below; they are not official exam questions or a replacement for the current syllabus.
BOD₅ measures the oxygen consumed by biological degradation of organic matter over 5 days at 20 °C. Ultimate BOD (L₀) is the total oxygen demand. The first-order model gives BOD_t = L₀(1 − e^(−k t)), where k is the decay rate constant. COD includes both biodegradable and non-biodegradable oxidizable matter.
Check yourself: Is the given BOD a 5-day value or the ultimate value?
Total hardness is the sum of calcium and magnesium hardness, expressed as mg/L of CaCO₃ equivalent. Carbonate hardness corresponds to alkalinity; non-carbonate hardness is the excess. Chlorine dosage equals chlorine demand plus the desired residual. Breakpoint chlorination requires dosing past the demand curve.
Check yourself: Have you converted Ca²⁺ and Mg²⁺ concentrations to CaCO₃ equivalents using their equivalent weights?
Primary treatment removes settleable solids by sedimentation. Secondary biological treatment (activated sludge, trickling filters) removes dissolved organics. Detention time equals tank volume divided by flow rate. The food-to-microorganism (F/M) ratio and sludge age characterize activated sludge operation.
Check yourself: Is the removal efficiency applied to the influent concentration or the load?
Common air pollutants include particulate matter, SO₂, NOₓ, CO, and O₃. Electrostatic precipitators and bag filters remove particles; scrubbers remove gases. The Gaussian plume model estimates ground-level concentration from a point source under steady wind, assuming the plume spreads normally in the crosswind and vertical directions.
Check yourself: Are the emission rate, wind speed, and dispersion coefficients in compatible units?
Municipal solid waste generation is expressed as mass per capita per day. Composting requires aerobic conditions and a suitable C:N ratio (roughly 25:1 to 30:1). Environmental Impact Assessment identifies, predicts, and evaluates impacts before project approval; it follows a structured process including screening, scoping, and public participation.
Check yourself: Does the calculation use generation rate, collection efficiency, or disposal capacity?
Original teaching example · not a PYQ
Original mini-example: a wastewater sample has BOD₅ = 150 mg/L at 20 °C. The first-order decay rate constant is k = 0.23 per day (base e). Assume the standard first-order BOD model. Find the ultimate BOD (L₀).
Ultimate BOD (L₀) ≈ 219.5 mg/L.
A water sample has Ca²⁺ = 80 mg/L and Mg²⁺ = 24.3 mg/L. What is the total hardness as CaCO₃? Use equivalent weight of CaCO₃ = 50, Ca = 20, Mg = 12.15.
Total hardness = 300 mg/L as CaCO₃.
Calcium hardness = 80 × (50/20) = 200 mg/L as CaCO₃. Magnesium hardness = 24.3 × (50/12.15) ≈ 100 mg/L as CaCO₃. Total hardness = 200 + 100 = 300 mg/L as CaCO₃.
Supplemental reading, not an official GATE reading list or an endorsement of these notes.
Free video lectures covering water quality parameters, treatment processes, and wastewater engineering aligned with the GATE CE environmental engineering syllabus.
Free supplemental course covering water treatment fundamentals, disinfection, and sanitation systems with lecture notes.
This page shows 60 recent questions from the released archive, newest first. For older questions and complete papers, browse all GATE CE papers. Questions can carry more than one subject tag; counts are not marks weightage.
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