Earth's Resources and Potable Water (C10.1)

Earth's resources

The Earth provides:

• Finite (non-renewable): fossil fuels (coal, oil, gas), metal ores, minerals — will eventually run out.
• Renewable: solar, wind, tidal energy, biofuels, timber (if managed sustainably).

Sustainable development: meeting current needs without compromising the ability of future generations to meet theirs.

Potable water

Potable water is water that is safe to drink — low levels of dissolved salts, low microorganism count, appropriate pH (~6.5–8.5), no harmful pollutants.

Note: potable ≠ pure water. Pure water contains no dissolved substances; potable water may contain some minerals.

Obtaining potable water in the UK (fresh water):

1. Collect water from reservoirs, lakes, rivers, groundwater.
2. Sedimentation: large particles settle.
3. Filtration: sand filter removes fine particles.
4. Chlorination: chlorine gas or sodium hypochlorite added → kills microorganisms (disinfection).
5. pH adjusted if needed.

Obtaining potable water from salt water (desalination):

• Distillation: very energy-intensive → expensive; used in water-scarce regions (Middle East).
• Reverse osmosis: water forced through semi-permeable membrane under pressure; removes dissolved salts. Energy-intensive but less than distillation.

Waste-water treatment

Sewage and industrial waste must be treated before returning to rivers:

1. Screening: large debris removed.
2. Sedimentation: solid sludge settles (primary sedimentation).
3. Biological treatment (trickling filters/activated sludge): bacteria break down organic matter.
4. Further sedimentation.
5. Treated water sterilised (chlorination/UV) and returned to environment.

Sludge is treated by anaerobic digestion → biogas (mainly methane — usable as fuel) + digestate (fertiliser).

Alternative metal extraction

Traditional smelting (reducing with carbon) is energy-intensive. Alternatives for low-grade ores:

Bioleaching:
Bacteria oxidise sulfide ores, releasing metal ions into solution (leachate). Metal extracted by displacement or electrolysis. Slow but low energy; can process low-grade ores.

Phytomining:
Plants absorb metal ions from soil; plants harvested and burned; metal extracted from the ash. Sustainable; can remediate contaminated land.

Common exam errors

1. Saying potable water is pure water — potable means safe to drink, not pure (distilled).
2. Forgetting that chlorination kills microorganisms (not removes particles — that's filtration).
3. Confusing bioleaching (bacteria) with phytomining (plants).