23-CS-3 Sustainability, Engineering and the Environment · December 2018
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams — December 2018 — 11-CS-3 Sustainability, Engineering and the Environment. Open book; non-communicating 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.
Complex, highly ordered materials embody large processing energy, so that investment should be preserved through reuse or remanufacture—e.g. remanufacturing a complex electronic module or engine rather than shredding it to base metals, preventing the pollution of making it anew.
Building in more capacity/capability than needed wastes materials and energy—e.g. specifying one oversized "one-size-fits-all" motor for many light duties runs it inefficiently in most; right-sizing (or a variable-speed drive) prevents that continuous energy waste.
Minimizing material diversity lets a product be disassembled and recycled cleanly—e.g. a single-polymer (mono-material) product or package can be recycled as one stream instead of being landfilled, retaining value and preventing waste.
Pollution prevention reduces or eliminates waste at the source. It cuts operating costs by (1) lower raw-material and energy use per unit (reducing purchasing and utility bills) and (2) lower waste-treatment, disposal, and compliance costs (avoiding the expense and liability of managing waste). P2 thus often pays for itself.
(i) Functional unit: providing one student's writing needs for the school year (e.g. the amount of writing that a set of disposable pencils, or one mechanical pencil plus refills, delivers). (ii) Stages: raw materials; manufacturing; distribution; use; end-of-life. (iii) Higher-impact alternative by stage (per functional unit, i.e. one student-year, assuming roughly 8–10 wooden pencils versus one mechanical pencil plus leads and erasers): Raw-material extraction — wood is higher: cedar/basswood harvesting, graphite-clay, paint and a metal ferrule for every one of the many pencils, whereas the mechanical pencil's small mass of petroleum-based plastic and steel is extracted once and the graphite leads weigh a few grams. Manufacturing — mechanical is higher per unit (injection-moulded plastic, a machined metal clutch and spring, more energy-intensive processes), but the wood pencils' repeated sawing, kiln-drying, lacquering and assembly for many units make the two comparable per student-year; the mechanical pencil's burden is a one-time investment. Distribution/packaging — wood is higher: many units (and repeated re-supply orders) are packaged and shipped through the year, against one pencil plus compact lead refills. Use — wood is slightly higher: sharpening turns a large fraction of each pencil into shavings (and electric sharpeners use power), while the mechanical pencil consumes only the lead actually written with. End-of-life — per unit the mechanical pencil is worse (mixed plastic and metal that persists in landfill and is hard to recycle), while the wooden stubs are a steady stream of waste (the wood biodegrades but the paint, ferrule and eraser do not); if the mechanical pencil is lost or broken early, its end-of-life burden multiplies. (iv) Stage of greatest impact: for the wood pencil, the recurring raw-material/manufacturing stage (many units made and shipped); for the mechanical pencil, its one-time manufacturing (plastic/metal body), amortized over a year of refills. The mechanical pencil is generally preferable if it genuinely replaces many disposables and is not itself discarded prematurely.
The triple bottom line holds that true sustainability requires performing acceptably in three dimensions simultaneously: economic (profit/prosperity—financially viable), social (people—fair, healthy, benefiting society and workers), and environmental (planet—protecting resources and ecosystems). A system, product, or process is genuinely sustainable only if it is sound on all three; success on one at the expense of another (e.g. profit through pollution) is not sustainable.
