GATE Water and Wastewater Treatment and Management: Water and Wastewater Quality – Previous Year Questions

6 GATE previous year questions on Water and Wastewater Quality (Water and Wastewater Treatment and Management, Environmental Science and Engineering) with answers and explanations, from every paper.

1. GATE 2022 ES Q45 (2 marks, Multiple select) – Rivers X, Y have reaeration constants .92,1.12 day⁻¹ and deoxygenation constants .23,.35 day⁻¹ respectively. Select correct statements.
2. GATE 2023 ES Q58 (2 marks, Numerical answer) – A BOD bottle contains 25 mL wastewater diluted to 300 mL. Wastewater ultimate BOD75 mg/L, initial diluted DO6.5 mg/L, and day 7 DO1.25 mg/L;day 5 was…
3. GATE 2024 ES Q12 (1 mark, Multiple choice) – Which listed ion does NOT cause water hardness?
4. GATE 2024 ES Q46 (2 marks, Multiple select) – Which are Streeter–Phelps oxygen-sag assumptions?
5. GATE 2026 ES Q30 (1 mark, Multiple select) – Total Kjeldahl Nitrogen includes which forms of nitrogen? Select all that apply.
6. GATE 2026 ES Q41 (2 marks, Multiple choice) – A water sample has Na+,Ca2+,Mg2+,Cl-,SO 42-,NO 3- concentrations 30,10,15,30,60,5 mg/L respectively. Atomic weights (g/mol) are Ca 40,Mg 24,Na 23,Cl…