Environmental Pollution and Control
What this domain tests
This domain covers air, water, soil, noise, thermal and radioactive pollution: sources, effects, monitoring and control. The exam tests BOD, COD, pH, particulate matter, AQI, wastewater treatment, the 3Rs and cleaner production.
Core rules and concepts
- Pollution is the introduction of a contaminant that causes harm or exceeds assimilative capacity.
- BOD measures oxygen consumed by microbes decomposing organic matter; COD measures oxygen demand of both biodegradable and many non-biodegradable substances. COD is generally higher than BOD.
- Primary treatment removes solids; secondary treatment uses biological processes; tertiary treatment removes nutrients or specific pollutants.
- Air pollution control includes cyclones, scrubbers, electrostatic precipitators, bag filters and catalytic converters; prevention includes fuel switching and efficiency.
- Noise is measured in decibels, a logarithmic scale; a 10 dB rise is about a tenfold increase in sound intensity.
Worked example
A factory discharges 1,000 L day⁻¹ of wastewater with BOD 300 mg L⁻¹. BOD load = 300 mg L⁻¹ × 1,000 L = 300,000 mg = 0.30 kg day⁻¹. After treatment to 30 mg L⁻¹, load = 0.03 kg day⁻¹. Removal = (0.30 − 0.03) ÷ 0.30 × 100 = 90%. Reason: load depends on both concentration and flow, so dilution changes concentration but not necessarily total load.
Traps that cost marks
Do not equate BOD with COD. Dilution is not treatment. PM10 and PM2.5 are size fractions, not chemical names. A pH of 5 is ten times more acidic than pH 6, not twice. Noise controls must consider duration and distance, not only peak level.