23-CS-3 Sustainability, Engineering and the Environment · December 2014
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams — December 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.
Using a single material (mono-material design) instead of many bonded, dissimilar ones lets a product be cleanly disassembled and recycled rather than landfilled—e.g. an all-one-polymer package or housing—retaining material value and preventing waste.
This principle says a product's performance should be judged partly by its value after its first use. Example: designing a photocopier, engine, or electronic device so that at end of first life its components can be readily remanufactured or refurbished and resold—e.g. modular, standardized, easily-inspected parts—so the product has a productive "second life" instead of becoming waste. Designing for remanufacture prevents the pollution and resource use of making everything anew.
Design a product to last exactly its intended service life—e.g. single-use items from compostable materials rather than permanent plastics—so it does not persist as waste beyond its usefulness.
The IPAT equation expresses environmental impact as $I = P \times A \times T$, where I is the environmental Impact, P is Population (number of people), A is Affluence (consumption or GDP per person), and T is Technology (environmental impact per unit of consumption). It shows that impact grows with population and affluence but can be reduced by cleaner, more efficient technology.
(i) Functional unit: delivering a defined amount of electrical energy to power the camera over a defined period—e.g. "the batteries required to supply the camera's energy needs over one year (or a fixed number of amp-hours)." This is essential because one rechargeable NiMH cell replaces many single-use alkaline cells. (ii) Stages: raw-material extraction; manufacturing; distribution; use (for NiMH, the electricity for repeated recharging plus the charger); and end-of-life. (iii) Higher-impact alternative by stage: in raw materials and manufacturing, single-use alkaline is worse over the functional unit because dozens of cells must be manufactured to match one rechargeable; in the use phase, NiMH carries the (small) burden of charging electricity and the charger; at end-of-life, single-use generates far more spent-battery waste (and NiMH contains recoverable metals), though both require proper battery recycling to avoid heavy-metal contamination. (iv) Stage of greatest impact for each: for single-use alkaline, the repeated manufacturing stage (and disposal volume); for NiMH, the manufacturing of the more complex cell, amortized over many cycles. Over any realistic number of recharge cycles the rechargeable is environmentally preferable, because its higher per-unit manufacturing burden is spread over hundreds of uses.
Design for disassembly: designing products to be easily taken apart at end of life for repair, reuse, or recycling. Industrial ecology: designing industrial systems like natural ecosystems so one process's waste is another's input. Reverse manufacturing: systematically disassembling used products to recover components and materials for remanufacture or recycling. Pollution prevention: reducing or eliminating waste at the source rather than treating it afterward. Intrinsic hazard: the inherent capacity of a substance/design to cause harm (toxicity, flammability, reactivity). Intangibles: real but hard-to-quantify costs or benefits such as reputation, aesthetics, or quality of life.
