NivaarExam PrepOfficial exam papers ↗

18-Env-A1 Principles of Environmental Engineering · May 2014

Question 5 of 7: Air Toxics Control and Solid Waste Management Planning

Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)

Notes on this paper

National Exams — May 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 5: Air Toxics Control and Solid Waste Management Planning (20 marks)

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.

(i) Three Air-Toxics Control Methods

Air toxics control methods: advantage, limitation and best application
MethodAdvantageLimitationBest Application
Activated-carbon adsorption (fixed source)Very high removal efficiency for VOCs (benzene, acetone) at low-to-moderate concentration; recoverable solvent if regeneratedCarbon bed saturates and must be regenerated/replaced; poor performance at high humidity or high VOC loadingSolvent-use industries (printing, degreasing) with dilute, intermittent VOC streams
Thermal/catalytic oxidation (fixed source)Near-complete destruction of VOCs (>95–99%) rather than transfer to another medium; catalytic version runs at lower temperature/fuel costFuel-cost and $\text{NO}_x$ trade-off at high temperature; catalyst poisoning by particulates or certain compoundsContinuous, moderate-to-high-concentration VOC streams (paint-curing ovens, chemical process vents)
Baghouse fabric filtration / catalytic converters (fixed-source PM, mobile-source $PM_{2.5}$/CO/HC)Very high $PM_{2.5}$ collection efficiency (baghouse, >99%); catalytic converters simultaneously cut CO, HC and $\text{NO}_x$ from vehicle exhaustBaghouse: pressure-drop and bag-replacement maintenance; converter: requires unleaded fuel and proper operating temperature, does not address fine PM from brake/tire wearBaghouse for fixed-source particulate (cement, metals processing); catalytic converters mandated on all light-duty mobile sources

The three methods span the two broad control strategies engineers choose between: capture-and-destroy (thermal/catalytic oxidation, converting the toxic to $\text{CO}_2$/$\text{H}_2\text{O}$) versus capture-and-collect (adsorption, filtration, which concentrates the pollutant for disposal or recovery) — the choice is driven mainly by concentration, flow rate and whether the recovered material has value.

(ii) 25-Year Solid Waste Management Plan

With only five years of remaining landfill capacity against a 25-year planning horizon, the plan cannot rely on landfilling alone and must combine waste reduction with new capacity and processing infrastructure, sequenced so that diversion measures reduce the tonnage that must ultimately be landfilled or processed at a new facility.

  1. Waste reduction and diversion (source reduction, recycling and organics diversion). Expanding curbside recycling and introducing mandatory organics/green-bin collection (composting or anaerobic digestion of food and yard waste) typically diverts 40–60% of the residential waste stream from disposal, directly extending the life of remaining capacity and aligning with provincial waste-diversion targets (e.g., Ontario's/CCME's waste-diversion and circular-economy frameworks) that set numeric diversion-rate objectives municipalities must report against.
  2. Extraprovincial engineering options for the disposal shortfall (new engineered landfill cell or waste-to-energy). Siting and permitting a new, properly engineered landfill cell (composite liner, leachate collection and treatment, methane gas collection) takes years, so the plan must begin the environmental assessment and site-selection process immediately; alternatively or in combination, a waste-to-energy facility recovers energy from the residual (non-divertible) waste stream and further reduces the volume requiring landfilling, both of which must meet air-emission standards under provincial regulation.
  3. Landfill gas capture and beneficial use. The existing (near-capacity) site and any new cell should have an engineered gas-collection system to capture methane (a potent greenhouse gas and odour/safety concern) for flaring or beneficial use (electricity generation or pipeline injection), which is now a standard regulatory expectation for large landfills under federal/provincial methane-reduction regulations.
  4. Extended producer responsibility and waste-reduction bylaws. Working with provincial extended-producer-responsibility (EPR) programs (packaging, electronics, tires) shifts disposal responsibility and cost upstream to producers, reducing the tonnage entering the municipal stream before it ever reaches the landfill gate, and supports the "reduce" tier of the pollution-prevention hierarchy ahead of "treat/dispose."

Each strategy is explicitly tied to a regulatory hook — provincial diversion targets, landfill design/liner standards, air-emission limits for waste-to-energy, and methane-reduction regulations — so that the plan is not just technically sound but demonstrably compliant with the environmental quality standards the local regulator will use to evaluate the new capacity.