18-Env-A6 Solid Waste Engineering and Management · May 2015
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.
A life cycle analysis (LCA) of a proposed composting operation should account for burdens and credits across the full cradle-to-end-use chain, not just the composting process itself. Energy inputs include collection-vehicle fuel, and electricity/diesel for shredding, turning and screening equipment at the facility. Emissions must capture both process emissions (N₂O and, where anaerobic pockets form, CH₄ generated within the compost pile itself) and the avoided emissions credit for diverting organics from landfill, where the same material would otherwise generate landfill methane over decades — typically the single largest credit in a composting LCA. Water use covers moisture added to maintain the 50–60% process target and any runoff/leachate management at the facility. Transportation factors in both the inbound haul distance from collection routes to the facility and the outbound distribution distance of finished compost to end users, since a facility sited far from either can erode much of the process's net environmental benefit.
Land use accounts for the facility's operational footprint over its service life. Product substitution/end-use credit recognizes that finished compost displaces synthetic fertilizer and, in some markets, peat moss, avoiding the upstream energy and emissions of manufacturing those substituted products — another significant credit. Finally, residuals and rejects (contaminants, oversize material screened out) must be tracked as a debit, since this fraction typically still requires landfill disposal and its LCA burden should not be attributed to the diverted, composted fraction. A complete LCA weighs these credits (avoided landfill methane, avoided fertilizer manufacture) against these burdens (collection/processing energy, process emissions, residuals disposal) on a common functional-unit basis, typically per tonne of organic waste diverted.
