18-Env-A6 Solid Waste Engineering and Management · December 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.); Freeze & Cherry, Groundwater; 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.
Both alternatives recover the same target materials — paper/fibre, containers, organics — but shift the cost, quality and behavioural burden to a different point in the system, so the evaluation has to weigh technical, economic, institutional and social factors together rather than picking on capital cost alone.
Recovered-material quality and market value. Source (at-home) separation into clean streams (blue-bin fibre, commingled containers, green-bin organics) yields a higher-purity, higher-value feedstock with less contamination and cross-material breakage than a mixed-waste stream sorted mechanically at an MRF, which must contend with broken glass contaminating paper, food residue on recyclables, and film plastics fouling sorting equipment. Higher purity translates directly into better resale price and fewer rejected loads.
Capital and operating cost, and who bears it. Source separation shifts the sorting labour to the household (free to the utility) but requires the community to fund and operate a multi-stream collection fleet (separate trucks or compartmentalized trucks, more collection routes/time). An MRF concentrates the capital cost into one facility (conveyors, screens, eddy-current and optical sorters, balers, a trained workforce) but allows single-stream ("dirty-recyclables") collection with one truck type, cutting collection cost at the expense of sorting cost and residue (reject) disposal cost.
Participation rate and behavioural reliability. Source separation depends entirely on sustained household compliance — participation rates fall over time without ongoing public education, enforcement (set-out audits) and convenient container design, and contamination rises when residents are unsure what belongs in which bin. An MRF is insulated from this human-behaviour risk: recovery depends on equipment performance and staffing, not on thousands of independent household decisions, at the cost of needing more aggressive (and imperfect) mechanical/optical separation technology.
Diversion rate achievable and range of materials. A well-run MRF, especially with mixed-waste processing, can often achieve a numerically higher diversion rate because it captures material from non-participating households too; but it recovers a narrower, lower-grade product mix than a well-participating source-separation program, which can extend to compostable organics that an MRF cannot mechanically sort out of a mixed refuse stream.
Siting, permitting and community acceptance. An MRF is a fixed facility requiring land, a siting/permitting process, traffic and noise considerations and community buy-in (similar concerns to landfill siting, see Question 12); source separation requires no new facility but does require sustained public-education investment and enforcement capacity within the municipality.
Flexibility to changing markets and waste composition. Source-separated streams are easier to reconfigure (add a new stream, e.g. glass-only, by changing bin colours and public messaging); an MRF's sorting line is a fixed capital asset and re-tooling it for a new material stream (e.g. adding film-plastic recovery) is a capital project, not a policy change.
