Social and environmental impact

Explain what the life cycle assessment of a product is and list its main stages, from cradle to grave. Why can looking only at the use phase give a false impression of the real impact?

The figure shows the life cycle of a mobile phone with one stage covered. State which stage is missing and describe two environmental impacts that occur in it.

Compare the life cycle of a returnable glass bottle with that of a single-use plastic bottle: impacts in extraction and manufacturing, transport (glass is heavier), number of uses, and end of life. Explain which factor usually tips the balance in favour of the returnable bottle.

Define the carbon footprint of a product and explain why it is expressed in $\text{kg}$ of CO₂ equivalent (the sum of all greenhouse gases converted to their CO₂ equivalent). Give an example of a daily activity and its approximate footprint.

Explain what the water footprint of a product is (water consumed throughout its life cycle) and why a cotton T-shirt can 'embody' more than $2\,000\ \text{L}$ even if manufacturing it barely gets it wet. What is the difference between green water (rainwater), blue water (irrigation), and grey water (pollutant dilution)?

A sustainability report for a rucksack uses four indicators: energy ($\text{MJ}$), emissions ($\text{kg CO₂ eq}$), water ($\text{L}$), and waste generated ($\text{kg}$). Explain why a single indicator is insufficient (an option may win on carbon and lose on water), what indicator weighting is, and what subjectivity it introduces.

Explain what an official ecolabel is (such as the EU Ecolabel) and how it differs from a 'green' advertising claim: who awards it, against what verifiable criteria, and what guarantee it offers consumers.

Distinguish between reduce, reuse, and recycle with an example of packaging for each verb, and explain why the waste hierarchy orders options in precisely this way (the best option is the one that avoids generating waste).

Life cycle assessments of shopping bags yield surprising results: a cotton bag must be used tens or hundreds of times to match the per-use impact of a plastic bag. Analyse the factors that explain this threshold (cotton farming: water and pesticides; transported weight; actual number of reuses) and what practical conclusion you draw for your own shopping.

Explain the difference between a linear economy (take, make, use, dispose) and a circular economy, and describe three circular loops (maintenance and repair, whole-product reuse, material recycling) with a product example for each loop. Why is the shortest loop (repairing) usually the most efficient?

Two mobile phone manufacturers approach the design of a device with opposing philosophies:

• Device X: Unibody chassis sealed with waterproof thermal adhesive (IP68), ultra-thin fixed non-removable battery, and components integrated into a single motherboard.

• Device Y: Modular chassis assembled with standard Torx screws (IP54), user-replaceable battery in 2 minutes, and independent modules (camera, USB port, screen) connected via ribbon cables.

• Analyze the life cycle of both devices: what advantages and disadvantages do they present in the use phase regarding drops/water, and at the end of life for recycling rare earth elements (neodymium, tantalum)?

• An official Repairability Index awards Model X a score of $3,8/10$ and Model Y an $8,9/10$. Justify which four technical criteria this index weights to penalize Device X.

• Suppose the manufacturer of Y stops updating the operating system after 3 years, while X provides software support for 7 years. Predict how this gap in planned/perceived obsolescence alters the actual sustainability estimated in the physical design.

In 2012, a city's passenger car fleet had an average fuel consumption of $6,5\text{ l}/100\text{ km}$, and each vehicle was driven $10\,000\text{ km/year}$. In 2024, thanks to improvements in injection systems and engine downsizing, the mechanical efficiency of internal combustion engines improved by $28\,\%$. However, the widespread purchase of SUV-type vehicles increased the average mass by $30\,\%$ and the frontal area by $15\,\%$, resulting in an actual consumption of $5,8\text{ l}/100\text{ km}$. Furthermore, as the fuel cost per kilometer became cheaper, the average distance traveled increased to $12\,500\text{ km/year}$.

1. Quantitatively calculate the percentage change in total fuel consumed per vehicle per year and interpret the result in light of Jevons' Paradox (rebound effect).

2. Break down the factors of the direct rebound effect (user behavior) and indirect rebound effect (product design/sizing) in this case.

3. The city council proposes subsidizing the purchase of mild hybrid SUVs (MHEV) to reduce pollution. Justify technically why this measure will worsen the problem, and design a regulatory proposal based on physical vehicle parameters (weight, footprint, consumption per passenger-km) to neutralize the rebound effect.

Explain what an impact assessment report is and what minimum sections it must contain (description of the technology, identified impacts, corrective measures, and conclusions). Who writes it and who uses it to make decisions?

A data centre consumes electricity for its servers and almost as much again to cool them. Explain what the PUE indicator is (the ratio of total energy to IT equipment energy), what value indicates an efficient centre, and three measures to improve it (free cooling, location in cold climates, waste heat reuse).

A municipality is debating replacing $50$ high-pressure sodium (HPS) streetlights of $150\text{ W}$ with $45\text{ W}$ LED luminaires. The streetlights operate $4\,100\text{ h/year}$. The electricity cost is $0,18\text{ \euro/kWh}$ and the grid emission factor is $0,22\text{ kg CO}_2\text{/kWh}$. The purchase and installation of each LED costs $190\text{ \euro}$ and its manufacturing generates $48\text{ kg CO}_2\text{eq}$. The current luminaires have 4 years of useful life remaining; removing them and managing them as waste generates $2,5\text{ kg CO}_2\text{eq}$ per point.

1. Calculate the economic payback period and the carbon payback time of the investment.

2. The councilor states: "Replacing streetlights that still work is anti-ecological because usable equipment is being discarded and manufacturing new units has already polluted." Refute or confirm his statement with technical data by calculating the net balance of $\text{CO}_2$ emissions over the 4 years of remaining life of the HPS streetlights.

3. Predict how the inclusion of a telemanagement system that dims the luminous flux to $50\,\%$ for $5\text{ h}$ at night in the LEDs would affect the sizing and environmental payback.