Chem

Potable water is a vital resource for life. Potable water is water that is safe to drink. Not much of earth's water is potable.

Type of water-

• Pure water- Water molecules and nothing else
• Potable water- Water molecules, low levels of salts, safe levels of harmful microbes
• Salty water- water molecules, with dangerously high levels of salt, can have high levels of harmful microbes 
• Freshwater (from rivers, lakes, or underground)- water molecules, low levels of salt, often have harmful microbes at high levels

Wastewater- Human activities produce lots of wastewater as sewage, agriculture waste and industrial waste.

• Sewage and agricultural waste contain organic matter and harmful microbes.

• Industrial waste contains organic matter and harmful chemicals.

These must be removed before the water can be put back into the environment.

Natural and synthetic resources- 

We use the Earth’s resources to provide us with warmth, fuel, shelter, food, and transport.

• Natural resources are used for food, timber, clothing, and fuels.

• Synthetic resources are made by scientists. They can replace or supplement natural resources.
When choosing and synthesising resources, it is important to consider sustainable development. This is a development that meets the needs of current generations without compromising the ability of future generations to meet their own needs.

Finite and renewable resources-
Some resources are finite. This means that they will eventually run out.
 Fossil fuels are an example of a finite resource. They take so long to form that we use them faster than they are naturally formed. 
Resources that will not run out are called renewable resources. 
Wood is an example of a renewable resource. Trees can be grown to replace any that are cut down for wood.

Metal extraction- metals can be extracted from their ores by reduction or electrolysis. However, metal ores are a finite resource and these processes require lots of energy. Scientists are looking for new ways to extract more sustainable metals. 
Phytomining and bioleaching are two different processes that are being developed to extract copper from low-grade ores (these are ores with only a little copper in them).

Phytomining- 1. Grow plants near the ore, 2. Harvest and burn the plants, 3. The ash contains a metal compound, 4. Process the ash by electrolysis or displacement with scrap metal.

Bioleaching- 1. grow bacteria near the metal ore, 2. Bacteria produce leachate solutions that contain metal compounds, 3. Process the leachate by electrolysis or displacement with scrap metal.

Both of these methods avoid the digging, moving, and disposing of large amounts of rock associated with traditional mining techniques.

Freshwater- In the UK, potable water is produced from rainwater that collects in lakes and rivers. To produce potable water:

1. Choose an appropriate source of fresh water.

2. Pass the water through filters to remove large objects.

3. Sterilise the water to kill any microbes

Salty water- Some countries do not have lots of fresh water available. Desalination is the process of turning saltwater into potable water. This requires a lot of energy and can be done by:

• distillation

• reverse osmosis

Reverse osmosis involves using membranes to separate the salts dissolved in the water. The water needs to be pressurised and the salty water corrodes the pumps. As such, it is an expensive process.

Wastewater-

Human activities produce lots of waste water as sewage, agricultural waste, and industrial waste.
• Sewage and agricultural waste contain organic matter and harmful microbes.
• Industrial waste contains organic matter and harmful chemicals.
These must be removed before the water can be put back into the environment.

Treating sewage water- 1. screening and grit removal, 2.Sedimentation- The sewage is left so that solid sediments settle out of the water. The sediments sink to the bottom of the tank. The liquid sits above the sediment.

 Treating Sludge- 1. sewage sludge This sediment is called sludge. Sludge contains organic matter, water, dissolved compounds, and small solid particles. 2. Anaerobic treatment- Bacteria are added to digest the organic matter. These bacteria break down the matter anaerobically – with a limited supply of oxygen. 3, Biogas- The anaerobic digestion of sludge produces biogas. Biogas is a mixture of methane, carbon dioxide and hydrogen sulfide. It can be used as fuel.  4, remaining sludge used as fuel- The remaining sludge can be dried out and can also be burnt as fuel.

Treating effluent- 1, effluent- The remaining liquid is called effluent. This effluent has no solid matter visible but still contains some matter and harmful microorganisms.2, aerobic treatment- Bacteria are added to the effluent. These bacteria feed on organic matter and the harmful microorganisms in the effluent. The bacteria break down the matter by aerobic respiration – oxygen needs to be present. 3, bacteria removed- The bacteria are allowed to settle out of the water.4, discharged back to rivers- The water is now safe enough to be released back into the environment.