Exercises: 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.

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?

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 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).

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)?

Compare the per-passenger impact of a Madrid–Barcelona trip by plane and by high-speed train, explaining which phase of the flight accounts for most emissions (take-off) and why the source of the train's electricity matters in the comparison.

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.

An electric car produces no tailpipe emissions, but its battery accounts for a large portion of its manufacturing impact. Explain what the initial 'carbon debt' of an electric vehicle is compared to an internal combustion vehicle, what determines the mileage at which the balance evens out (electricity grid mix, battery size), and what practical conclusion can be drawn.

Identify three social impacts of factory automation (direct employment, new technical roles, working conditions) and three environmental impacts (energy consumption, electronic waste, material efficiency), and write a balanced conclusion for the assessment report.

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.

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).

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?

Analyse the life cycle of a standalone solar streetlight: manufacturing impacts (panel, lithium battery, pole), use phase (emissions?), and battery end-of-life. Compare it with a grid-connected streetlight and explain in which situations the solar light is clearly advantageous and in which it is not.

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.

A university cafeteria serves $120\,000$ coffees a year and compares two service systems through a Life Cycle Assessment (LCA):

• Option A (Disposable): Paper cup with a compostable PLA lining. Manufacturing and transport footprint: $24\text{ g CO}_2\text{eq}$ and $0,25\text{ l}$ of water per unit. When disposed of in a landfill or composting facility, it generates $16\text{ g CO}_2\text{eq}$.

• Option B (Reusable): Injection-molded polypropylene cup ($40\text{ g}$). Manufacturing footprint: $320\text{ g CO}_2\text{eq}$ and $3,2\text{ l}$ of water. Washing in an on-site commercial dishwasher consumes $0,35\text{ l}$ of water and generates $9\text{ g CO}_2\text{eq}$ of energy per cycle. A loss or breakage rate of $2\,\%$ per use is estimated.

• Calculate the environmental payback threshold (minimum number of uses a reusable cup must last to emit less total $\text{CO}_2\text{eq}$ than the equivalent disposables).

• Interpret the impact of the loss rate: if students lose the cup before the 15th use, predict which option generates a greater carbon impact and which generates a greater water footprint.

• Design two technical or operational management measures for the cafeteria to ensure that the reusable option is environmentally viable.

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.

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.

A comparative LCA is conducted between two garments intended for the same functional use:

• Garment S (Virgin polyester, fast fashion): Manufacturing: $4,5\text{ kg CO}_2\text{eq}$ and $150\text{ l}$ of water. Estimated lifespan: $12$ wears/washes before tearing or losing its shape.

• Garment N (Durable organic cotton): Manufacturing: $8,2\text{ kg CO}_2\text{eq}$ and $2\,700\text{ l}$ of water (farming and spinning). Estimated lifespan: $75$ wears/washes.

Each domestic washing and drying cycle generates $0,18\text{ kg CO}_2\text{eq}$ and consumes $25\text{ l}$ of water. In each wash, Garment S sheds approximately $1\,800$ non-biodegradable synthetic microfibers.

1. Define the appropriate Functional Unit to make a fair comparison and calculate the carbon footprint ($100$ wears) for both textile systems.

2. Interpret the environmental trade-off: justify why evaluating only the manufacturing water footprint would lead to an incorrect conclusion about which one is more sustainable.

3. Design two technical modifications (one in the spinning process/textile design and another in the home appliance maintenance phase) aimed at mitigating the specific negative externality of microplastic shedding in Garment S.

A combined cycle power plant supplies electricity and heat to an industrial district, emitting $0,36\text{ kg CO}_2\text{/kWh}$ and $110\text{ mg NO}_x\text{/Nm}^3$. The healthcare, social, and atmospheric acidification costs not paid by the company (negative externality) are estimated at $0,028\text{ \euro/kWh}$. To correct this, the government is evaluating two internalization policy instruments:

• Instrument A: Direct environmental tax (Pigouvian tax) of $0,028\text{ \euro/kWh}$.

• Instrument B: Tradable emission permits market with an annual cap reduction (cap-and-trade) of $4\,\%$.

• Predict how each instrument will incentivize plant engineers: under what technical conditions will they choose to install selective catalytic reduction (SCR) systems instead of passing the cost on to users' energy bills?

• If the company passes $100\,\%$ of tax A on to the price of the kilowatt-hour, analyze why a regressive social impact occurs on low-income residential consumers, and justify how to structure a "carbon dividend" to correct it.

• Demonstrate why a flat tax does not guarantee an absolute emission cap during a period of economic growth, whereas a cap-and-trade system does.

A fast-food chain annually replaces $200\,000$ sets of polystyrene (PS) cutlery with two alternatives:

• Option 1: Polylactic acid (PLA), biodegradable under industrial composting (temperature $>58\text{ }^\circ\text{C}$ and controlled humidity for 60 days). In the region, only $18\,\%$ of the collected organic fraction is treated in composting plants with these specifications; the rest goes to landfill or incineration.

• Option 2: Birch wood with a vegetable wax coating. Its processing requires $3$ times more land area and $2,5$ times more water than PLA, but it biodegrades in soil or home compost in $90$ days.

• Analyze the "burden shifting" phenomenon: predict what mechanical and environmental problems will occur if users dispose of the PLA cutlery in the yellow container for conventional plastic packaging (PET/PE).

• Based on the waste management data of the region, justify which of the two options offers a more favorable real ecological balance at the end of life.

• Evaluate the technical feasibility of replacing disposable cutlery with stainless steel cutlery using a Deposit-Refund System (DRS). Determine which infrastructure limiting factors (washing space, local water/energy consumption, loss rate) must be audited to validate its implementation.

An electric vehicle manufacturer must select the cell chemistry for a new urban fleet:

• NMC cell (Nickel-Manganese-Cobalt): Energy density of $250\text{ Wh/kg}$. Each $60\text{ kWh}$ battery requires $9\text{ kg}$ of cobalt, largely originating from mining associated with severe human rights impacts and water pollution in the DR Congo. Its hydrometallurgical recycling is economically profitable due to the high market value of cobalt and nickel.

• LFP cell (Lithium Iron Phosphate): Energy density of $155\text{ Wh/kg}$. It uses abundant iron and phosphorus without cobalt or nickel. Being less dense, the battery weighs $61\,\%$ more for the same capacity, increasing vehicle consumption by $1,2\text{ kWh/100 km}$. Its recycling is currently running at a loss.

• Present the environmental justice conflict: analyze the trade-off between local extractive justice (human rights and mining degradation in exporting countries) and global climate impact during the use phase.

• Predict the geographical destination of the batteries at the end of their useful life: if LFP recycling is not spontaneously profitable through the market, what risk of transboundary waste trafficking to developing countries is generated if Extended Producer Responsibility (EPR) is not enforced?

• Propose two technical and regulatory specifications (such as the Digital Battery Passport or mandatory percentages of recycled content in new cells) that would allow the use of NMC chemistry while verifiably mitigating social externalities at origin.