23-Chem-B2 Environmental Engineering · December 2013
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Paper format. EGBC 04-Chem-B2 Environmental Engineering, December 2013, 3 hours, closed-book with a candidate-prepared double-sided 8½×11-inch aid sheet. Seven problems, each worth 20 marks; candidates attempt any five, and only the first five answers in the workbook are marked. All seven problems are solved below as a complete study resource.
Reference texts: G. Tchobanoglous, F. L. Burton & H. D. Stensel (Metcalf & Eddy), Wastewater Engineering: Treatment and Reuse (4th ed., McGraw-Hill) — BOD kinetics, dissolved air flotation, activated-sludge design, nutrient removal; M. L. Davis & D. A. Cornwell, Introduction to Environmental Engineering (5th ed., McGraw-Hill) — drinking-water treatment, air pollution control, ion exchange, reverse osmosis, soil remediation; C. D. Cooper & F. C. Alley, Air Pollution Control: A Design Approach — membrane/condensation/adsorption control technologies, thermal oxidation, odour control; S. P. Turner, Workbook of Atmospheric Dispersion Estimates (2nd ed., CRC Press) — the Gaussian plume model and Pasquill–Gifford stability classes. Canadian context follows the Canadian Environmental Protection Act (CEPA 1999), the Canadian Council of Ministers of the Environment (CCME) Municipal Wastewater Effluent and Drinking Water Quality guidelines, and provincial air/water permitting practice (e.g. BC Environmental Management Act, Metro Vancouver air-quality bylaws), which govern effluent/emission limits and treatment-technology selection referenced throughout.
Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.
A comparative matrix, as recommended by the question, is the clearest way to present the three control-technology families side by side.
| Technology | Main design principle | Advantages (2) | Limitations (2) | Example industrial process |
|---|---|---|---|---|
| (i) Membrane filtration (particulates) | The gas (or liquid) stream is forced through a microporous polymeric or ceramic membrane; particles larger than the membrane's pore size are physically rejected at the membrane surface (sieving), while the carrier fluid passes through — unlike a fabric filter's depth/cake filtration, separation is governed primarily by the fixed pore-size cutoff of the membrane itself. | Extremely sharp size cutoff gives very high, consistent removal efficiency even for sub-micron particles; compact footprint compared with an equivalent baghouse or ESP for the same gas volume. | Membrane fouling (cake buildup, pore blinding) progressively raises pressure drop and requires backwashing or periodic membrane replacement; higher capital cost per unit throughput than conventional fabric filtration, and membranes are vulnerable to chemical/thermal degradation outside a narrower operating window. | Ceramic membrane filtration of hot process off-gas in cement or metals processing, or crossflow membrane polishing of fine particulate from a pharmaceutical/semiconductor cleanroom exhaust. |
| (iii) Condensation (gases) | The gas stream is cooled (or compressed) below the dew point of the target vapour-phase pollutant, driving it to condense out of the gas phase into a recoverable liquid; the achievable removal is set by the pollutant's vapour-pressure curve at the operating temperature/pressure, so condensation is only effective for pollutants with a sufficiently high concentration and a boiling point not too far below ambient. | Recovers the pollutant as a liquid product (often solvent-recovery credit that partially offsets operating cost) rather than merely destroying it; no chemical reagent consumption, unlike absorption or oxidation. | Ineffective at reducing concentration below the pollutant's saturation vapour pressure at the coldest practical operating temperature, so it typically cannot reach very low outlet concentrations alone (often paired with a polishing adsorption step); refrigeration/compression energy cost rises sharply for pollutants with low boiling points. | Solvent-vapour recovery from a printing, degreasing, or tank-farm vapour-recovery system (e.g. recovering chlorinated or hydrocarbon solvent vapour for reuse). |
| (iv) Adsorption (odorous vapours) | The odour-laden gas is passed through a bed of a high-surface-area sorbent (typically activated carbon, sometimes impregnated with an oxidant for reduced-sulfur odorants); odorant molecules are retained on the internal pore surface by van der Waals/physisorption (or chemisorption for impregnated media) until the bed reaches breakthrough, at which point it is regenerated (steam/thermal swing) or replaced. | Very effective down to extremely low (ppb-level) odour-threshold concentrations, which is exactly the regime where odour complaints occur even though the mass loading is trivial; simple, passive equipment with no moving parts in the bed itself. | Adsorption capacity is finite and the bed requires monitoring/regeneration or replacement on a breakthrough schedule; humidity and competing (non-odorous) VOCs in the stream can co-adsorb and prematurely exhaust capacity for the target odorant. | Activated-carbon adsorption of H₂S/mercaptan odours from a wastewater headworks or biosolids-handling building exhaust, or VOC/odour polishing on a rendering-plant exhaust. |
