Earth's Resources: Water, Pollution and Sustainability
Finite and Renewable Resources
The Earth provides natural resources that humans depend on for warmth, shelter, food and transport. Finite resources (also called non-renewable) will eventually be exhausted because they are consumed faster than they form. Examples include fossil fuels (which took millions of years to form) and metal ores mined from the Earth’s crust. Renewable resources can be replaced at roughly the same rate they are used — examples include timber from managed forests, crops, wind energy, solar energy and hydroelectric power.
Sustainable development means meeting the needs of today’s population without depleting resources that future generations will depend on. Chemistry plays a central role: designing industrial processes with higher atom economy, developing renewable and biodegradable materials, improving recycling technology, and creating more energy-efficient production routes all contribute to a more sustainable future.
Sustainable development: meeting current needs without compromising the ability of future generations to meet theirs. It requires using finite resources wisely, recycling, reducing waste, and developing renewable alternatives.
Potable Water
Potable water is water that is safe to drink. It is not chemically pure — it still contains dissolved mineral salts — but has sufficiently low levels of dissolved substances and harmful microorganisms to be safe for human consumption. In the UK, most potable water is produced from fresh water sources such as rivers, lakes and reservoirs, through a multi-stage treatment process.
Step 1: Filtration — the water is passed through filter beds (layers of gravel and sand) to remove large solid particles and debris, including some suspended solids.
Step 2: Sterilisation — to kill harmful bacteria and microorganisms, the water is treated using chlorine, ozone, or ultraviolet (UV) light. Chlorine is the most commonly used method in the UK because it is effective, relatively cheap, and its residual effect continues to kill bacteria as the water travels through the distribution network to homes. Ozone and UV are used in some systems but provide no residual protection once the water leaves the treatment plant.
The treated water is then tested to ensure it meets drinking water standards before being distributed. The quality standards are set to protect public health.
Desalination
In countries with limited fresh water, potable water must be produced from sea water or brackish water. Desalination achieves this by removing dissolved salts. Two main methods are used:
Distillation: the sea water is heated until it boils, the water vapour is condensed and collected, leaving the dissolved salts behind. Reverse osmosis: sea water is forced under high pressure through a membrane that allows water molecules through but blocks dissolved salt ions. Both methods require large amounts of energy, making potable water produced by desalination considerably more expensive than that produced from fresh water. In the UK, where rainfall is generally sufficient, fresh water treatment is the primary approach. In arid regions, desalination is essential despite the high energy cost.
Desalination produces potable water from sea water by distillation (boiling and condensing) or reverse osmosis (high-pressure membrane filtration). Both methods require large amounts of energy, making desalinated water much more expensive than water treated from fresh sources.
Treating Waste Water
Waste water from homes, industry and agriculture must be treated before being returned to rivers or the sea, to prevent pollution and protect aquatic ecosystems. Sewage treatment is a multi-stage process involving both physical and biological methods.
1. Screening — large solid objects such as rags and sticks are removed by passing the sewage through coarse screens and grit channels. 2. Primary sedimentation — the screened sewage flows slowly through large settlement tanks. Heavier solids sink to form sludge, while lighter grease floats to the surface. Both are removed. 3. Biological treatment — the remaining liquid passes through aeration tanks where aerobic microorganisms break down dissolved organic matter. This biological stage is essential for removing dissolved organic pollutants. The sludge from sedimentation is also treated separately: anaerobic bacteria digest it, producing biogas (mainly methane) which can be used as a fuel. 4. Final clarification and sterilisation — the cleaned water undergoes further sedimentation, then is sterilised before being safely released into rivers.
Industrial waste water may contain heavy metals or toxic organic compounds and requires specialised treatment before release. Agricultural run-off containing nitrate fertilisers can cause eutrophication in waterways — excessive algal growth that depletes oxygen and harms aquatic life — if not properly managed.
Haber Process and NPK Fertilisers
Ammonia produced by the Haber process is a starting material not only for direct use as a fertiliser but for the production of NPK fertilisers — compound fertilisers containing nitrogen, phosphorus and potassium in specific ratios. Nitrogen is provided by ammonium compounds or urea (both derived from ammonia), phosphorus from processed phosphate rock, and potassium from potash (potassium-containing minerals). These three elements are essential for healthy plant growth: nitrogen for leaf and stem growth, phosphorus for root development and energy transfer, and potassium for flower, fruit and disease resistance. The correct balance of N, P and K varies with soil type and crop, and is determined by soil analysis.
NPK fertilisers supply three key plant nutrients: nitrogen (N) for growth of leaves and stems, phosphorus (P) for root development and energy processes, and potassium (K) for flowers, fruits and disease resistance. Ammonia from the Haber process is the nitrogen source.
Sustainability in Resource Use
Sustainable management of Earth’s resources includes: reducing consumption of finite resources, recycling to recover valuable materials, developing biodegradable alternatives to persistent plastics, and improving industrial processes to reduce waste and pollution. The principle applies across every sector — from agriculture (sustainable fertiliser use to prevent eutrophication) to water management (reducing leakage and improving efficiency) to manufacturing (designing products for disassembly and recycling at end of life). Balancing economic development with environmental protection remains one of the central challenges of the 21st century.