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18-Env-A6 Solid Waste Engineering and Management · May 2017

Question 9 of 16: Life-Cycle Analysis of a Composting Facility

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

Notes on this paper

National Examination, May 2017 — 04-Env-A6 / 18-Env-A6, Solid Waste Engineering and Management. 3 hours duration, closed book, non-communicating calculator permitted. All 16 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; ISO 14040/14044, Environmental Management — Life Cycle Assessment.

Q6 below is solved from the six printed per-component rows, which are unambiguous exam-given data — see the callout at Q6 for the arithmetic. Table 2's "5.800 kJ/kg" organics value (period instead of comma) is read as 5,800 kJ/kg.

Question 9: Life-Cycle Analysis of a Composting Facility (5 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.

9.1 Benefits of conducting a Life-Cycle Analysis. An LCA quantifies the full environmental footprint of a system across its entire life cycle rather than at just one process step, revealing burden-shifting that a narrow facility-gate comparison would miss (e.g. a process that looks clean on-site but relies on high-emission upstream transport or inputs). It provides a defensible, standardized (ISO 14040/14044) basis for comparing genuinely different technology options — here, composting against landfilling or incineration — on a consistent functional-unit basis, supports credible avoided-emissions/avoided-product credits (e.g. compost displacing synthetic fertilizer), and identifies which life-cycle stage dominates the impact, focusing limited engineering/design effort on the change that will actually move the result.

9.2 Variables for an LCA of an MSW composting facility. The inventory should capture: feedstock composition and quantity (source-separated organics vs. mixed MSW, moisture content, C:N ratio); energy inputs (fuel for collection/haul, electricity and diesel for turning/aeration equipment); water inputs (added during processing to maintain moisture); land area occupied by the pad/facility; process emissions (fugitive CH₄ and N₂O from anaerobic pockets in poorly-aerated piles, VOCs and odour, leachate/runoff from the composting pad); transport distances (feedstock collection haul and finished-compost distribution haul); outputs (finished compost mass and quality, and the residual "contraries" fraction rejected to landfill); and avoided-impact credits (compost displacing synthetic fertilizer manufacture, and diverted organics avoiding landfill methane generation).

In practice the two sub-questions are linked: the benefits identified in 9.1 (defensible technology comparison, avoided-emissions crediting) are only realized if the inventory in 9.2 is complete enough to capture the dominant impact — omitting transport distances or the avoided-fertilizer credit, for instance, would undermine the very comparison-basis benefit that makes conducting the LCA worthwhile in the first place.