Environmental Engineering
Environmental Engineering covers water demand, treatment, wastewater characteristics, BOD/COD, sedimentation, filtration, disinfection, and air and solid-waste management. The exam tests process design and numerical dilution problems.
Core rules
- Per-capita water demand for Indian cities is commonly taken as 135 lpcd, with peak factors applied to design supply.
- BOD measures oxygen consumed by microorganisms; COD measures oxygen equivalent of chemically oxidisable matter; COD ≥ BOD.
- BOD of a diluted sample: BOD = (D₁ − D₂) × dilution factor, where dilution factor = volume of diluted sample/sample volume.
- Sedimentation removes settleable solids; filtration removes fine particles; disinfection inactivates pathogens.
- Detention time = volume/flow; overflow rate = flow/surface area.
Worked example
A 5 mL wastewater sample is diluted to 300 mL. Initial DO D₁ = 8 mg/L and final DO D₂ = 2 mg/L after 5 days. Dilution factor = 300/5 = 60. BOD₅ = (8 − 2) × 60 = 360 mg/L. If seeded dilution water is used, subtract the seed correction before multiplying by the dilution factor.
Traps that cost marks
- Reversing the dilution factor.
- Treating COD and BOD as interchangeable.
- Forgetting seed correction in seeded BOD tests.
- Using surface overflow rate and detention time interchangeably.
Exam focus
Practise BOD/COD calculations, sedimentation basin sizing, and the sequence of conventional water-treatment units.