Using Resources

Definition: Potable Water

Potable water is water that is safe to drink and does not contain harmful microorganisms or toxic substances.

It is not "pure" because it contains low levels of dissolved salts, which are safe for consumption.

Treatment Process

Methods depend on the water source and country. Standard steps for fresh water include:

1. Source selection: Usually from rivers, lakes, or aquifers.
2. Filtration: Passed through filter beds to remove insoluble solids.
3. Sterilisation: Microbes are killed using Chlorine, Ozone, or UV light.

Desalination

Used in desert regions or countries with very limited fresh water supplies. Salt is removed via distillation or reverse osmosis. Both are expensive because they require massive amounts of energy.

The 4 Mandatory Stages

Before sewage can be released back into the environment, it must undergo these steps:

1. Screening: Removes large objects like twigs, grit, and plastic.
2. Sedimentation: Heavier solids settle out as sludge, leaving liquid effluent on top.
3. Aerobic Digestion: Air is pumped through effluent; bacteria break down organic matter in the presence of oxygen.
4. Anaerobic Digestion: Sludge is broken down without oxygen. This produces methane gas, which can be used as a renewable fuel to generate electricity.

[Image of the stages of wastewater treatment]

Sustainable Mining

Traditional mining causes significant environmental damage, such as habitat destruction and air pollution. These alternative methods extract copper from low-grade ores:

• Phytomining: Plants absorb metal ions into their roots. The plants are harvested and burnt; the resulting ash contains a high concentration of the metal.
• Bioleaching: Bacteria break down ores to produce a solution called a leachate, which contains metal ions.

Evaluating Environmental Impact

LCAs track the impact of a product through 4 stages: Raw material extraction, Manufacture, Use, and Disposal.

[Image of Life Cycle Assessment flowchart]

Limitations

LCAs are not purely objective because:

• Assigning values to pollutants involves subjective judgement.
• LCAs may be incomplete because some environmental impacts are difficult to quantify with exact data.

Ammonia Production

This process produces ammonia for fertilisers. The reaction is reversible and exothermic.

$$ N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g) $$

Compromise Conditions

Condition	Value	Reasoning (Le Chatelier)
Pressure	200 atm	Higher pressure shifts equilibrium to the right (fewer molecules) to increase yield.
Temperature	450°C	Exothermic reaction; low temp gives higher yield but 450°C is a compromise for a faster rate.
Catalyst	Iron	Increases the rate of reaction but has no effect on the yield.

Agricultural Productivity

Fertilisers increase crop yield by providing essential elements for healthy plant growth.

• N (Nitrogen): For leaf growth and proteins.
• P (Phosphorus): For roots and flowers.
• K (Potassium): For overall hardiness.