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.
Key issues: (1) feedstock supply and quality — a reliable, adequately source-separated organics stream (low contamination from plastics/glass) is essential, requiring an upstream collection and public-education program; (2) process design and control — carbon-to-nitrogen ratio, moisture content, aeration/turning frequency and temperature must be actively managed to sustain thermophilic composting (see Question 18) without odour generation or incomplete stabilization; (3) siting and buffer distance — odour and bioaerosol generation make siting and community acceptance a significant issue, similar in kind to landfill and combustion-facility siting (Questions 12 and 15); (4) process residuals and contaminant screening — non-compostable contaminants (plastic film, glass) must be screened from the feedstock and the finished residue disposed of; (5) finished-product quality and market — compost must meet a recognized quality standard (e.g. CCME/provincial compost guidelines for pathogen reduction, maturity and contaminant limits) to be marketable as a soil amendment; and (6) capital/operating cost and facility scale relative to the available feedstock volume and the diversion targets the facility is meant to serve.
Because composting is highly sensitive to feedstock contamination, the upstream and downstream issues are more tightly coupled here than for most other diversion technologies: a facility sized correctly on paper can still fail commercially if plastic-film or glass contamination in the incoming organics stream degrades the finished compost below the quality standard needed to sell it, so the public-education/collection-quality program (issue 1) and the finished-product market (issue 5) have to be planned together from the very outset, not sequenced as separate, later-stage problems. A useful early step is a pilot collection program covering a subset of the community before full-scale rollout, letting the contamination rate and resulting compost quality be measured against real local behaviour before the full facility's capital budget is committed.
