Term
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Definition
| Water that is unsuitable for drinking, irrigation, industrial use or washing. |
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Term
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Definition
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Term
| What are water pollutants in sewage? |
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Definition
| Heavy metals, pesticides, dioxins, PBCs, organic matter, nitrates and phosphates |
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Term
| What are the main sources of water pollution? |
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Definition
| Batteries, detergents, industrial processes and agricultural processes |
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Term
| What is the purpose of sewage treatment? |
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Definition
| To remove disease-causing microorganisms, organic materials and toxic substances and to reduce the BOD. |
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Term
| Describe primary sewage treatment. |
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Definition
| Water is filtered and allowed to settle twice (can be sped up with aluminium sulphate), then Cl2 or O3 is used to kill bacteria. |
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Term
| What is the problem with primary sewage treatment? |
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Definition
| Not sufficient to improve the water quality to a safe level, barely removes BOD waste |
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Term
| Describe secondary sewage treatment. |
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Definition
| Like primary sewage treatment, but it uses an aeration tank where aerobic bacteria oxidise and break down organic matter (activated sludge process) |
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Term
| What is the problem with primary and secondary sewage treatment? |
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Definition
| They both do not remove dissolved inorganic substances such as nitrates, phosphates and heavy metal ions. |
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Term
| Decribe tertiary sewage treatment. |
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Definition
| Uses carbon beds, chemical precipitation and/or anaerobic biological processes. |
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Term
| What is the carbon-bed method? |
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Definition
| It uses activated carbon granules with high surface area to absorb organic chemicals and purify the water. |
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Term
| What is chemical precipitation? |
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Definition
| Uses H2S to convert heavy metals into their sulphides which can be easily removed: M + H2S -> MS + 2H. Phosphates are reduced with calcium ions. |
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Term
| What are anaerobic biological processes? |
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Definition
| Denitrification; denitrifying bacteria reduce nitrates to nitrogen gas. |
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Term
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Definition
| The removal of salt from seawater. |
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Term
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Definition
| The process of heating the salt water creating fresh water as vapour and a salt precipitate. |
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Term
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Definition
| The movement of water molecules from areas of high concentrations to those of lower concentration across a semipermeable membrane. |
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Term
| How can osmosis be reversed? |
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Definition
| By increasing the osmotic pressure in the area of low concentration (seawater), so more water molecules move to the fresh water. |
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