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18-Env-A6 Solid Waste Engineering and Management · May 2014

Question 21 of 22: Strategies to Derive Energy from Municipal Wastes

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

Notes on this paper

National Examination, May 2014 — 04-Env-A6 / 18-Env-A6, Solid Waste Engineering and Management. 3 hours duration, closed book, no calculator, one letter-sized aid sheet permitted. All 22 questions constitute a complete paper (100 marks total).

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 21: Strategies to Derive Energy from Municipal Wastes (2 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.

(1) Direct thermal conversion (waste-to-energy) — mass-burn or refuse-derived-fuel (RDF) incineration of the combustible fraction, recovering heat as steam and/or electricity. (2) Biological conversion to biogas — anaerobic digestion of the organic fraction (or landfill-gas recovery from an existing landfill, capturing the methane generated by in-situ anaerobic decomposition) for combustion in a boiler or engine-generator. Both routes displace fossil-fuel energy that would otherwise be purchased and reduce the volume/mass of waste that must ultimately be landfilled, but they suit different fractions of the waste stream: thermal conversion works best on the dry, high-heating-value fraction (paper, plastics, wood), while biological conversion works best on the wet, readily biodegradable organic fraction that would otherwise burn poorly and lower a combustor's overall efficiency.