18-Env-A1 Principles of Environmental Engineering · December 2014
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams — December 2014 — 04-Env-A1 / Principles of Environmental Engineering. 3 hours duration; closed book with an 8.5×11 in double-sided aid sheet; Casio or Sharp approved calculator only. Any five questions constitute a complete paper (first five answers marked); all seven are solved below for completeness. Each question is worth 20 marks.
Reference texts. Davis & Cornwell, Introduction to Environmental Engineering (6th ed.); Metcalf & Eddy, Wastewater Engineering: Treatment and Resource Recovery (5th ed.); MWH’s Water Treatment: Principles and Design (3rd ed.); Guidelines for Canadian Drinking Water Quality (Health Canada); Canadian Council of Ministers of the Environment (CCME) water-quality guidelines; Canadian Environmental Protection Act, 1999 (CEPA); Andrews, Canadian Professional Engineering and Geoscience (professional ethics).
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.
| Method | Advantage | Limitation | Best Application |
|---|---|---|---|
| Activated-carbon adsorption | Very high removal efficiency for VOCs (benzene, acetone) at low-to-moderate concentration; recoverable solvent if the bed is thermally regenerated | Carbon bed saturates and must be regenerated or replaced; poor performance at high humidity or high VOC loading | Solvent-use industries (printing, degreasing, coating) with dilute, intermittent VOC streams |
| Thermal/catalytic oxidation | Near-complete destruction of VOCs (>95–99%) rather than transfer to another medium; catalytic version runs at lower temperature and fuel cost | Fuel-cost and $\text{NO}_x$ trade-off at high combustion temperature; catalyst poisoning by particulates or certain compounds | Continuous, moderate-to-high-concentration VOC streams (paint-curing ovens, chemical process vents) |
The two methods span the two broad control strategies engineers choose between for a fixed source: capture-and-collect (adsorption, which concentrates the pollutant for disposal or recovery) versus capture-and-destroy (thermal/catalytic oxidation, converting the toxic to $\text{CO}_2$/$\text{H}_2\text{O}$) — the choice is driven mainly by concentration, flow rate and whether the recovered material has value.
The three terms describe progressively more (or differently) enforceable expressions of the same underlying water- or air-quality target, and the distinction matters directly to how an environmental engineering design is specified and defended. A quality objective is a numeric or narrative goal set for a specific water body or airshed reflecting its intended use (e.g., a dissolved-oxygen objective of 6 mg/L set for a specific salmon-bearing reach to protect that use); it is site-specific and aspirational, not itself a legal discharge limit. A quality guideline (e.g., the CCME Water Quality Guidelines, or the Guidelines for Canadian Drinking Water Quality) is a generic, science-based numeric or narrative benchmark developed nationally for a given use (protection of aquatic life, drinking water), intended to inform the setting of local objectives and permits but not, on its own, legally binding. A quality standard is a legally enforceable numeric limit, typically embedded in a discharge permit or regulation (e.g., a specific $\text{BOD}_5$/TSS effluent limit written into a municipal wastewater treatment plant's operating permit under provincial legislation) that a facility must meet or face regulatory enforcement.
The practical significance for design: an engineer designs a treatment facility to reliably meet the legally binding standard in its permit (the design basis), informed by the national guideline (used to set that standard's numeric value in the first place), while the local objective for the receiving water body explains why that particular numeric standard was chosen for that discharge rather than a generic one — a design that meets a generic guideline value but not the more stringent objective-derived standard for its specific, sensitive receiving water is non-compliant, even though it may satisfy the guideline in isolation.
