Environmental Engineering
Environmental Engineering covers water demand and treatment, wastewater characteristics, air pollution and solid-waste management.
Core rules
- Water demand is expressed in litres per capita per day (LPCD); peak factors account for hourly and daily variation.
- Conventional treatment: screening → coagulation-flocculation → sedimentation → filtration → disinfection. Chlorination CT depends on residual concentration and contact time.
- BOD5 is measured at 20°C over 5 days; dilution water and seed corrections are applied when the sample is strong.
- BOD exertion follows first-order kinetics: BODt = BODu(1 − e^(−kt)).
- Wastewater: activated sludge uses recycle and aeration; trickling filters are attached-growth; UASB is anaerobic.
- Air quality is managed through ambient standards and dispersion; PM10, SO2 and NOx are common indicators.
Worked example
A 5 mL wastewater sample is diluted to 300 mL. Initial DO is 8.0 mg/L; final DO after 5 days is 4.0 mg/L. Find BOD5. Dilution fraction P = volume of sample / total volume = 5/300 = 0.01667. BOD5 = (D1 − D2)/P = (8.0 − 4.0)/0.01667 = 240 mg/L. If the blank or seed correction were significant, it would be subtracted before dividing by P.
Traps
Inverting the dilution fraction; reporting COD as BOD; ignoring seed correction for industrial wastes; treating BOD as a conservative parameter; mixing LPCD with cumecs.