23-CS-3 Sustainability, Engineering and the Environment · May 2014
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams — May 2014 — 11-CS-3 Sustainability, Engineering and the Environment. Closed book; approved calculator permitted. Any four questions constitute a complete paper; all questions are of equal value (25 marks each).
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.
Reuse means using a product or component again in its existing form for the same or a different purpose, without reprocessing—e.g. refilling a returnable glass bottle. Recycling means reprocessing a used material back into raw material to manufacture new products—e.g. melting glass bottles to make new glass. The difference is that reuse keeps the item's form and embedded value intact (no reprocessing energy), whereas recycling breaks the item down to its material and remakes it, consuming energy in the reprocessing; reuse therefore sits above recycling in the waste hierarchy because it conserves more of the invested value.
Products of many bonded, dissimilar materials are hard to separate and recycle. Example: designing packaging or a product housing from a single polymer (mono-material) rather than a multilayer laminate of different plastics and foils, so it can be cleanly recycled instead of going to landfill—retaining material value and preventing waste.
Building in more capacity or capability than needed wastes materials and energy. Example: specifying one oversized "one-size-fits-all" motor or pump for many light duties makes it run inefficiently in most, wasting energy and emissions; right-sizing to the actual duty (or using a variable-speed drive) prevents that continuous waste.
A product should last only as long as its intended service life. Example: single-use items made from compostable/biodegradable materials rather than permanent plastics—durable enough for use, then degrading harmlessly instead of persisting as waste.
(i) Functional unit: the service of keeping one patient (infant) clean and dry for a defined period—e.g. all diaper-changes required per patient-day, or per patient stay—so the comparison reflects equal service (many disposables versus fewer cloth diapers reused many times). (ii) Stages: raw-material extraction; manufacturing; distribution/transport; use (for cloth, the laundering—water, energy, detergent—repeated over many cycles); and end-of-life (disposables to landfill; cloth eventually discarded). (iii) Higher-impact alternative by stage: in raw materials and manufacturing, disposables are worse because a new diaper is consumed at every change (pulp, superabsorbent polymer, plastics) whereas cloth is made once and reused; in the use phase, cloth is worse because of the repeated laundering (hot water, energy, detergent, and wastewater); at end-of-life, disposables dominate the burden as large volumes of non-degradable landfill waste, while cloth generates little. (iv) Stage of greatest impact for each: for disposables, the raw-material/manufacturing stage plus end-of-life landfill; for cloth, the use (laundering) stage. The overall winner depends on how the laundering is done (efficient, high-load washing and low-carbon energy favour cloth) and how many times the cloth is reused.
Design for disassembly: designing products so they can be readily taken apart at end of life for repair, reuse, or material recovery. Industrial ecology: designing industrial systems on the model of natural ecosystems, so one process's waste becomes another's input and materials cycle. Reverse manufacturing: the systematic disassembly of used products to recover components and materials for remanufacture, reuse, or recycling (the "reverse" of assembly). Pollution prevention (P2): reducing or eliminating waste and pollution at the source through better design and process efficiency, rather than treating it after creation. Intrinsic hazard: the inherent capacity of a substance or design to cause harm (its toxicity, flammability, reactivity), which green design seeks to reduce at source. Intangibles: costs or benefits (e.g. reputation, aesthetics, quality of life) that are real but difficult to quantify in monetary terms.
