23-Chem-B2 Environmental Engineering · May 2014
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Paper format. EGBC 04-Chem-B2 Environmental Engineering, May 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, nutrient removal, activated-sludge design, sedimentation design; 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, air quality modelling; C. D. Cooper & F. C. Alley, Air Pollution Control: A Design Approach — particulate/gas/vapour control, thermal/catalytic 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 Guidelines for Canadian Drinking Water Quality (Health Canada), the Canadian Council of Ministers of the Environment (CCME) Municipal Wastewater Effluent guidelines, and provincial air/water permitting practice (e.g. BC Environmental Management Act and Metro Vancouver air-quality bylaws).
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.
As recommended by the question, a comparative matrix presents the three contaminant-specific control technologies side by side.
| Contaminant / Technology | Main design principle | Advantages (2) | Limitations (2) | Example industrial process |
|---|---|---|---|---|
| (i) Particulates — electrostatic precipitator (ESP) | Particles pass between high-voltage discharge electrodes and grounded collection plates, acquire a negative charge by field/diffusion charging, migrate to the grounded plate under the applied field, and are collected then periodically rapped into a hopper. | Very high collection efficiency (>99%) across a wide size range, including sub-micron particulate; very low pressure drop compared with a fabric filter or scrubber, an important operating-cost advantage on huge continuous gas volumes. | Efficiency is sensitive to particle electrical resistivity (very high- or very low-resistivity dust collects poorly); large capital footprint and re-entrainment risk if rapping is not carefully timed. | Coal- or biomass-fired power-plant flue-gas particulate control. |
| (ii) Toxic gases — packed-bed absorption (chemical scrubbing) | The gas stream is contacted counter-currently with a reactive liquid (acid, base, or oxidant) in a packed column; the toxic gas transfers across the gas–liquid interface driven by Henry's-law solubility/reactivity and is neutralized or captured in the liquid. | Very effective for soluble/reactive acid or base gases (SO₂, HCl, NH₃, H₂S) even at low concentration; can recover a saleable by-product (e.g. gypsum from SO₂ scrubbing) while achieving compliance. | Generates a liquid waste stream requiring its own treatment/disposal; ineffective for gases with low solubility or reactivity unless an engineered reactive liquid is developed for that specific compound. | Flue-gas desulfurization (lime/limestone scrubbing) at a smelter or coal-fired power plant. |
| (iii) Odorous vapours — carbon adsorption | The odorous vapour-laden gas passes through a bed of activated carbon; odorous organic molecules are physically adsorbed onto the carbon's very high internal surface area (van der Waals forces), removing them from the gas stream until the bed's adsorption capacity is exhausted (breakthrough). | Very effective at very low odour-threshold concentrations where combustion/absorption are impractical; simple, passive, low-energy operation with no liquid waste stream generated. | Finite adsorption capacity requires periodic bed replacement or thermal regeneration, an ongoing operating cost; humidity and competing compounds in the gas stream reduce effective capacity for the target odorant. | Wastewater headworks or biosolids-handling building odour control (activated-carbon canisters on exhaust air). |
