11-CS-3 Engineering Management · May 2015
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams — May 2015 — 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.
Designing from a single material (mono-material) rather than bonded dissimilar materials lets a product be cleanly recycled rather than landfilled—e.g. an all-one-polymer package—retaining material value and preventing waste.
Design a product to last only its intended service life—e.g. single-use items from compostable materials rather than permanent plastics—so it degrades harmlessly instead of persisting as waste.
$I = P \times A \times T$: environmental Impact equals Population (number of people) × Affluence (consumption or GDP per person) × Technology (impact per unit of consumption). Impact rises with population and affluence but can be reduced by cleaner, more efficient technology.
Reuse uses a product again in its existing form without reprocessing (e.g. refilling a returnable bottle), preserving its embedded value. Recycling reprocesses the used material into raw material to make new products (e.g. melting the bottle for new glass), consuming reprocessing energy. Reuse sits above recycling in the waste hierarchy because it conserves more of the invested value.
(i) Functional unit: keeping one baby clean and dry for a defined period—e.g. all diaper-changes required per baby over the diapering years—so the many disposables are compared fairly with the few cloth diapers reused repeatedly. (ii) Stages: raw materials; manufacturing; distribution; use (for cloth, repeated laundering—water, energy, detergent); end-of-life. (iii) Higher-impact alternative by stage: raw materials/manufacturing—disposables worse (a new diaper per change: pulp, superabsorbent polymer, plastics); use—cloth worse (repeated hot-water laundering and wastewater); distribution—disposables worse (a continuous stream of bulky packaged product trucked to retailers, against a one-time purchase of a few dozen cloth diapers; home-laundered cloth has almost no distribution burden, though a diaper-service delivery van narrows the gap); end-of-life—disposables worse (several thousand soiled diapers per child go to landfill, where the plastic and superabsorbent persist and untreated faeces bypass sewage treatment, whereas worn-out cloth is a small quantity of largely biodegradable textile). (iv) Stage of greatest impact: for disposables, manufacturing plus landfill disposal; for cloth, the use (laundering) stage. The overall winner depends on laundering efficiency and energy source and on how many times the cloth is reused.
Design for disassembly: designing products to be easily taken apart for repair, reuse, or recycling. Emissions trading: a market-based system in which a cap is set on total emissions and tradable allowances let firms buy/sell the right to emit, achieving reductions at least cost. Industrial ecology: designing industrial systems like ecosystems so one process's waste becomes another's input. Reverse manufacturing: disassembling used products to recover components and materials. Pollution prevention: reducing/eliminating waste at the source. E-waste: discarded electrical and electronic equipment, a rapidly growing and hazardous waste stream containing toxic metals and recoverable materials. Natural capital: the stock of natural resources and ecosystems that yields a flow of valuable goods and services. Externalities: costs or benefits of an activity borne by third parties not reflected in its market price (e.g. pollution). Intangibles: real but hard-to-quantify costs/benefits such as reputation or quality of life.
