Environmental Engineering (Water Supply, Sanitary, Public Health)
Environmental Engineering covers water demand, treatment trains, distribution, sewage characteristics, biological treatment, sludge handling and public health. The WBPSC AE paper tests process design parameters from CPHEEO manuals and IS 10500, plus simple mass balances.
Core rules
- Water demand uses per capita demand, with peak factor 1.5–2.0 for distribution; fire demand is separate.
- Treatment: screening, aeration, coagulation-flocculation, sedimentation, filtration and disinfection.
- Sedimentation design uses surface overflow rate Q/A, not detention time alone.
- BOD₅=(D₁−D₂)×dilution factor for unseeded dilution; nitrification can inflate BOD.
- Activated sludge is controlled by F/M ratio, MLSS, sludge age and return sludge; secondary clarifier SOR is a key check.
Worked example
A sample is diluted 1:20. Initial DO is 8.0 mg/L and final DO is 4.0 mg/L. BOD₅=(8.0−4.0)×20=80 mg/L. If seeded dilution water consumed 0.5 mg/L, the seed correction is subtracted before multiplying. For a 2000 m³/d flow, BOD load is 80 mg/L×2000 m³/d=160 kg/d.
Traps
- Using a 1:20 dilution as a factor of 5 instead of 20.
- Forgetting seed correction.
- Mixing MLD and m³/d.
- Designing sedimentation only by detention time while ignoring SOR.
- Treating chlorination as a substitute for filtration.