18-Env-A5 Air Quality and Pollution Control Engineering · December 2014
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams — December 2014 — 04-Env-A5 / Air Quality and Pollution Control Engineering. 3 hours duration; closed book with a candidate-prepared 8½×11 in double-sided aid sheet; Casio or Sharp approved calculator only. Any five (5) questions constitute a complete paper (the first five answers as they appear are marked); all seven are solved below for completeness. Each question is worth 20 marks with section marks shown in brackets.
Reference texts. Cooper & Alley, Air Pollution Control: A Design Approach (4th ed.); Wark, Warner & Davis, Air Pollution: Its Origin and Control (3rd ed.); Davis & Cornwell, Introduction to Environmental Engineering (6th ed.); Canadian Environmental Protection Act, 1999 (CEPA) and the Canadian Ambient Air Quality Standards (CAAQS) administered by Environment and Climate Change Canada.
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.
Benzene (from fuel evaporation, incomplete combustion, and solvent/petrochemical operations) is a genotoxic human carcinogen, causally linked to acute myeloid leukemia and other blood dyscrasias, with no established safe threshold of exposure. An effective engineering strategy is vapour recovery at every transfer point — floating-roof storage tanks (eliminating the vapour space above the liquid) combined with balanced (return-line) vapour recovery during tank truck loading/unloading, which captures benzene-laden vapour that would otherwise vent directly to atmosphere and routes it to a carbon adsorber or the vapour-recovery unit for recondensation.
Mercury (released mainly from coal combustion, where trace Hg in the coal volatilizes in the flame and partly remains as elemental/oxidized vapour through the flue-gas train) is a potent neurotoxin, bioaccumulating as methylmercury in aquatic food chains and causing developmental neurological damage, particularly in children exposed in utero. An effective engineering strategy is activated-carbon injection (ACI) upstream of the particulate control device: powdered activated carbon (often halogen-impregnated to target elemental Hg0) is injected into the flue gas, adsorbs the mercury species, and the loaded carbon is then captured along with fly ash in the downstream ESP or baghouse.
A biofilter is the standard biotechnology for food-processing odour control (e.g., rendering, coffee roasting, or bakery/fermentation off-gas rich in reduced-sulphur and volatile fatty-acid odorants). Process design: odorous exhaust air is first humidified/conditioned (typically through a spray humidification chamber) to bring it to near-saturation, since the biologically active layer requires consistent moisture (40–60% by weight) to function. The conditioned air is then ducted, at low, evenly distributed face velocity, up through a packed bed of an organic support medium (compost, bark mulch, or a compost/perlite blend) that hosts an acclimated biofilm of odour-degrading bacteria and fungi. As the air percolates through the bed, odorous compounds partition from the gas phase into the moist biofilm and are aerobically oxidized to CO2, water and biomass. Design is governed by the empty-bed residence time (EBRT, typically 15–60 s, set by bed depth and superficial velocity) and bed moisture/pH control; a well-designed biofilter routinely achieves 90–95%+ odour and VOC removal at a fraction of the capital and operating cost of thermal oxidation.
Emission trading (cap-and-trade) sets an overall regional or international emissions cap for a pollutant, allocates or auctions tradable allowances (each representing the right to emit one unit of pollutant) up to that cap, and lets sources buy and sell allowances among themselves. A source that can reduce emissions cheaply sells its surplus allowances to a source facing high abatement costs, so the cap-mandated total reduction is achieved at the lowest aggregate cost across the whole system, regardless of which individual facility does the reducing. Between international neighbours (the historical model being the Canada–U.S. Air Quality Agreement's acid-rain provisions, paralleling the U.S. Acid Rain Program's SO2 allowance trading), the mechanism additionally addresses transboundary pollution: because SO2/NOx emitted in one country contributes to acid deposition in the other, a jointly agreed cap with cross-border allowance recognition lets both countries share the compliance flexibility while still guaranteeing the combined transboundary load falls, avoiding the free-rider problem of one country reducing emissions while the other does not.
