Environmental Engineering and Pollution Control
Core concepts
Environmental control integrates with process design. Know air pollution basics: particulates and gases (SOx, NOx, CO, VOCs), dispersion (Gaussian plume, stack height, stability classes), and control devices (cyclones, baghouses, ESPs, scrubbers, catalytic converters). For water, understand BOD, COD, TSS, DO, and treatment trains (primary, secondary activated sludge, tertiary). Solid and hazardous waste management, incineration and landfilling, and the waste hierarchy (reduce, reuse, recycle, recover, dispose) are tested. Also cover effluent standards, the concept of dilution and assimilative capacity, greenhouse gases, and cleaner production. Noise and thermal pollution appear occasionally. Environmental legislation frameworks and EIA are conceptual topics.
Traps
BOD measures biodegradable organics (usually 5-day), COD measures chemically oxidisable matter; COD ≥ BOD typically. Do not confuse removal efficiency with outlet concentration. Cyclone efficiency rises with smaller cut diameter but pressure drop increases. Scrubbers handle gases and fine particles; ESPs are efficient for fine particulates but sensitive to resistivity. In dispersion, stable conditions reduce mixing.
Worked rule of thumb
Collection efficiency of a control device: η = (Cin − Cout)/Cin. For a series of devices, overall η = 1 − (1 − η1)(1 − η2)… A cyclone at 80% followed by a baghouse at 99% gives overall 1 − 0.2×0.01 = 99.8%.
Exam strategy
Identify the pollutant, its phase and the applicable standard, then select the control technology and compute efficiency.