23-Chem-B2 Environmental Engineering · December 2014
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Paper format. EGBC 04-Chem-B2 Environmental Engineering, December 2014, 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 — fabric filtration, thermal oxidation, adsorption, 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 application |
|---|---|---|---|---|
| (i) Fabric filters (baghouse) — particulates | Dust-laden gas is drawn through a woven or felted fabric bag; particles are captured on the growing surface cake (depth filtration during cake build-up, then surface/cake filtration once established), and the cake is periodically dislodged by pulse-jet, reverse-air, or mechanical shaking into a collection hopper. | Very high collection efficiency (>99%) across a wide particle-size range, including the sub-micron fraction that gravity settlers and cyclones cannot capture; relatively simple, well-understood technology with modular scale-up. | Pressure drop rises as the cake builds, requiring a defined cleaning cycle (too frequent re-entrains dust, too infrequent chokes flow); bag material is vulnerable to high temperature, moisture condensation (blinding), and chemical attack, restricting the operating envelope. | Baghouse dust control on a cement kiln, foundry, or grain-handling facility exhaust. |
| (ii) Thermal oxidizers — vapours | The vapour-laden gas stream is heated (directly fired, or via a recuperative/regenerative heat exchanger to recover energy from the hot outlet gas) to a temperature and residence time sufficient to oxidize the organic vapour to CO₂ and H₂O; a catalyst bed can lower the required temperature (catalytic vs. thermal/regenerative oxidation). | Can achieve very high (>99%) destruction efficiency for a broad range of VOCs/organic vapours regardless of chemical identity, unlike a technology tuned to one specific compound; regenerative designs recover a large fraction of the combustion energy, substantially cutting net fuel cost for dilute streams. | Significant auxiliary fuel cost for dilute vapour streams below their auto-thermal (self-sustaining) concentration; produces its own combustion by-products (NOx, and HCl if the vapour is chlorinated), which may require downstream acid-gas or NOx control. | Regenerative thermal oxidation (RTO) of solvent vapour from an automotive paint-booth or printing-press exhaust. |
| (iii) Adsorption towers — gases | The gas stream is passed through a packed bed of a high-surface-area sorbent (activated carbon, zeolite); target gas molecules are retained on the internal pore surface by physisorption (or chemisorption for an impregnated/reactive sorbent) until the bed approaches breakthrough, at which point it is thermally/steam regenerated or replaced, often using two parallel beds so one adsorbs while the other regenerates. | Very effective at recovering or removing gas-phase contaminants even at low (ppm-level) concentrations where combustion-based control becomes uneconomical; a non-regenerative or solvent-recovery adsorption system can recover the adsorbed compound as a saleable/reusable product. | Finite, saturable capacity requires a defined breakthrough-monitoring/regeneration schedule; competing co-adsorption of humidity or other gas-stream constituents can prematurely exhaust capacity for the target contaminant, and some regeneration methods generate a concentrated waste stream needing further treatment. | Activated-carbon adsorption of gasoline-vapour emissions at a fuel-storage/loading-rack vapour-recovery unit. |
