[Part 2]- C12- using resources ♻️

• waste water, is water that contains dangerous substances and toxins which is detrimental to the environment and human health.

• urban lifestyles [flushing toilets and washing clothes] and industrial processes [making paper or chemicals] produces large amounts of waste water, that requires treatment before being released into the environment

• sewage and agricultural waste water, require the removal of organic matter [e.g- urine and faeces] and harmful microbes [such as bacteria]

• sewage is first screened by passing through a mesh, to remove grit and solids

• the sewage is then settled in large sedimentation tanks, to produce a liquid effluent and sewage sludge [which sinks]

• sewage sludge is then taken away, and anaerobically digested by bacteria

• the liquid effluent is aerobically treated to reduce liquid effluent and harmful microorganisms [before it is returned to the environment]. • this is because, the liquid effluent contains large amounts of organic molecules and harmful microorganisms

• the treated liquid effluent is then safely discharged into nearby rivers, or into the sea

• air is bubbled through the liquid effluent, so aerobic bacteria can multiply and digest the organic molecules and harmful microorganisms

• in the absence of oxygen, anaerobic bacteria can produce biogas which can be produce for electricity

• digested sludge can be used as fertilisers for farming

• sewage is settled when it undergoes sedimentation • this means, the heavier suspended solids sink to the bottom of the sedimentation tank, to produce sludge whilst the lighter effluent floats on the top

• in some places in the world, treated sewage water is used to directly produce potable water

• ground water • salt water • and, waste water

• the easiest way to produce potable water, is to use ground water from aquifers • groundwater from aquifers is usually safe to drink, once it has been treated with chlorine

• because aquifers can sometimes be polluted [such as being polluted with fertilisers from farms]

• potable water can directly be produced from treating waste water; this takes many purification steps, which is expensive • therefore, obtaining potable water from waste water, is only done where water is scare

• the Earth’s resources of metal ores are limited because, millions of tons of metal ores are extracted from the Earth’s crust annually [every year] • this means metal ores such as copper are becoming scare [running out], so copper must be instead extracted from low-grade ores

• a metal ore contains enough metal to make it economical [cost effective], to extract metal

• low-grade ores only contain very small amounts of copper • this means, it is harder to extract copper economically from these ores

• phytomining and bioleaching avoid traditional miming methods of digging, moving and disposing of large amounts of rock

• phytomining, is when plants are used to absorb metal compounds

• bioleaching, is when bacteria produces leachate solutions that contain metal compounds

• plants first absorb the metal compound, and they concentrate it in their tissue • these plants are then harvested and burned; the ash contains a relatively high concentration of the metal compound