23-CS-3 Sustainability, Engineering and the Environment · December 2017
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams — December 2017 — 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.
Highly ordered, complex materials embody large processing energy (low entropy), so that investment should be preserved through reuse or remanufacture rather than destroyed. Example: reusing or remanufacturing a complex electronic assembly or engine preserves its embedded complexity, whereas shredding it to recover base metals discards it—preventing the pollution and energy of making a complex part anew.
Because separating mixed materials is the hardest, most energy-intensive step of recovery, it should be planned at the design stage. Example: designing a product so its materials part easily (snap-fits and a single polymer instead of glued composites), so end-of-life recycling needs no energy-intensive separation—preventing the waste that arises when mixed materials cannot be economically separated.
Pollution prevention (P2) is reducing or eliminating waste and pollution at the source—through process design, material substitution, and efficiency—rather than treating it after creation. It reduces operating costs in two clear ways: (1) lower raw-material and energy costs—using less material and energy per unit (and recycling in-process) directly cuts purchasing and utility bills; and (2) lower waste-management, treatment, and compliance costs—preventing waste avoids the expense of treating, storing, transporting, and disposing of it, plus regulatory fees and potential liability. P2 thus often pays for itself, aligning environmental benefit with cost saving (the "pollution prevention pays" principle).
(i) Functional unit: providing all the reading material one student needs over a defined period (e.g. several years of schooling)—so the many printed books are compared fairly with the one e-reader used repeatedly. (ii) Stages: raw materials; manufacturing; distribution; use (e-reader electricity for charging); end-of-life. (iii) Higher-impact alternative by stage: in raw materials and manufacturing, per functional unit the books are worse (paper, ink, and printing for many titles) though a single e-reader's electronics are energy- and toxics-intensive; in use, the e-reader carries the (small) charging energy; in distribution, heavy books are worse to ship; at end-of-life, books are recyclable/compostable while the e-reader is hazardous e-waste. (iv) Stage of greatest impact: for books, the recurring raw-material/manufacturing stage; for the e-reader, its one-time manufacturing. The e-reader is generally preferable if it replaces many books and is used for years.
Design for disassembly: designing products to be easily taken apart for repair, reuse, or recycling. Environmental purchasing policy: a procurement policy that preferentially buys goods and services with lower environmental impact (recycled content, energy efficiency, low toxicity), using purchasing power to drive greener supply. Reverse manufacturing: disassembling used products to recover components and materials. E-waste: discarded electronic equipment, a hazardous and fast-growing waste stream. Intangibles: real but hard-to-quantify costs/benefits such as reputation or quality of life.
