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

Question 4 of 16: Source Separation vs. MRF Separation

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 4: Source Separation vs. MRF Separation (10 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.

Evaluating source separation (households sort recyclables into designated streams before collection) against centralized separation (all waste collected commingled and sorted mechanically/manually at a materials recovery facility, MRF) requires weighing several linked factors. Recovered-material quality and marketability — source-separated material is typically less contaminated (no food/liquid mixing with paper or plastics) and commands a higher resale value, while commingled MRF-sorted material has higher contamination and lower quality, sometimes requiring double handling or facing rejection by end markets. Capital and operating cost split — source separation shifts capital cost into the collection side (multiple collection streams and vehicles, or a compartmentalized truck) while MRF separation concentrates capital in one centralized facility (screens, magnets, eddy-current and optical sorters) but keeps collection simple (single-stream). Participation and compliance — source separation depends on resident behaviour and diligence, and participation rates and set-out quality vary widely without sustained public education, whereas MRF separation removes that dependency (residents just discard waste as usual) at the cost of higher facility investment. Diversion/recovery rate achievable — a well-run MRF can often achieve higher overall material capture (it processes 100% of the waste stream rather than relying on voluntary participation), though its recovery of any single material stream is imperfect due to commingling losses. Collection logistics — multiple source-separated streams increase the number of collection routes/trucks (and therefore collection cost, which already dominates the SWM budget per Q3), whereas single-stream collection for MRF processing minimizes collection-side cost and complexity. The recommended system for most communities is a hybrid: source separation of the highest-value, easily-contaminated streams (e.g. organics, glass) combined with single-stream collection and MRF processing of the remaining commingled recyclables — balancing quality against collection cost.