18-Env-A6 Solid Waste Engineering and Management · May 2016
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Reference texts: Tchobanoglous, Theisen & Vigil, Integrated Solid Waste Management: Engineering Principles and Management Issues; Vesilind, Worrell & Reinhart, Solid Waste Engineering; Davis & Cornwell, Introduction to Environmental Engineering (6th ed.); CCME, Guidance Document on Landfill Gas Management; Canadian Environmental Protection Act, 1999.
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.
(1) Carbon:nitrogen (C:N) ratio — roughly 25–30:1 by mass, balancing readily available carbon (energy source) against nitrogen (needed for microbial cell synthesis); a ratio far outside this range slows decomposition or drives off excess nitrogen as ammonia. (2) Moisture content — roughly 50–60% by weight, enough to support microbial activity without saturating the pore space and excluding oxygen. (3) Oxygen supply (aeration) — sustained aerobic conditions throughout the pile, via turning or forced/passive air supply, to avoid odorous anaerobic pockets (Q4/Q5). (4) Particle size — small enough to provide adequate surface area for microbial attack, but not so fine that it collapses the pore space needed for air movement. (5) pH — near neutral, roughly 6.5–8.0, for optimal microbial activity across the bacterial and fungal populations involved. (6) Temperature — a sustained thermophilic range (roughly 55–65 °C) for pathogen and weed-seed destruction, without exceeding the range that inhibits the thermophilic organisms themselves.
