16-Civ-A3 Elementary Environmental Engineering · Undated paper
Question 6 of 7: Air-Pollution Control & Solid-Waste Management
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Notes on this paper
Paper format. National Exams, May 2019 — 16-Civ-A3 Elementary Environmental Engineering. Closed book (one 8.5″×11″ double-sided aid-sheet), 3 hours. Seven problems; any five constitute a complete paper (each 20 marks). All seven are solved here as a study resource.
Reference texts. Davis & Cornwell, Introduction to Environmental Engineering (5th ed.); Mihelcic & Zimmerman, Environmental Engineering: Fundamentals, Sustainability, Design (3rd ed.); Metcalf & Eddy, Wastewater Engineering: Treatment and Resource Recovery (5th ed.); MWH (Crittenden et al.), Water Treatment: Principles and Design (3rd ed.); CCME Canadian Environmental Quality Guidelines; Health Canada Guidelines for Canadian Drinking Water Quality; Impact Assessment Act (Canada, 2019).
Source note. The seven questions and their sub-part mark splits follow the paper’s own Marking Scheme (page 7): 1 (6/6/8), 2 (7/7/6), 3 (8/5/7), 4 (6/7/7), 5 (10/10), 6 (3/3/4 + 3/3/4), 7 (10/10) — each closing to 20 marks. Where a figure ordinate must be read off a plot it is flagged in a check callout.
Question 6: Air-Pollution Control & Solid-Waste Management (20 marks)
(a) Electrostatic precipitator (particulates). The dirty gas passes between discharge electrodes and grounded collecting plates; a high-voltage corona charges the particles, and the electric field drives the charged particles onto the plates (migration/drift velocity governs efficiency, per the Deutsch–Anderson relation). Rapping periodically dislodges the collected dust into hoppers. It achieves very high removal of fine particulates at low pressure drop.
(b) Wet scrubbing (SO2). The flue gas is contacted with an alkaline slurry/liquid (typically lime or limestone). SO2 absorbs into the liquid and reacts — $\text{SO}_2 + \text{CaCO}_3 + \tfrac12\text{O}_2 + 2\text{H}_2\text{O} \rightarrow \text{CaSO}_4\!\cdot\!2\text{H}_2\text{O} + \text{CO}_2$ — converting a gaseous pollutant into a solid gypsum by-product. Removal depends on gas–liquid contact area and liquid-to-gas ratio.
(c) Adsorption (NO2 / organic vapours). The gas passes through a bed of high-surface-area sorbent (activated carbon or a molecular sieve); pollutant molecules bind physically (or chemically) to the internal pore surface, so the exit gas is cleaned until the bed nears saturation (breakthrough), after which the bed is regenerated (thermal/steam or pressure swing) or replaced. Effective for dilute vapours and odours; NOx is more commonly reduced by selective catalytic reduction, noted as the industry-standard alternative.
6(ii) — Solid-waste management strategies.
(a) Storage and collection.Technical: provide covered, vermin-proof containers and source-separated streams (waste/recycling/organics), sized and routed for efficient collection frequency to prevent odour and litter. Non-technical: service-level policy, collection scheduling and public education on set-out practices.
(b) Materials recovery and recycling.Technical: a materials-recovery facility (MRF) with screens, magnets/eddy-current separators and optical sorting to recover marketable fractions; composting/anaerobic digestion for organics. Non-technical: extended-producer-responsibility and deposit-return programs, plus markets/procurement policy that create demand for recyclate — following the 3R hierarchy (reduce → reuse → recycle).
(c) Landfill leachate.Minimize generation: engineered final cap and grading to shed surface water, run-on/run-off controls, and diversion of clean water to keep it out of the waste mass. Treat what forms: a low-permeability liner and leachate-collection system route leachate to on-site treatment or to a WWTP; recirculation (bioreactor operation) can accelerate stabilization. Groundwater monitoring wells confirm containment.
