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Water - SQA Key Definitions :
Water - SQA Key Definitions :
- Anaerobic digestion - The biological process in which microorganisms break down biodegradable material (such as sewage sludge) in the absence of oxygen.
- Biogas - The flammable gas methane, created by the anaerobic digestion of the sludge.
- Biological oxidation - The chemical breakdown of organic waste by bacteria, converting it into energy & new bacterial biomass.
- Blackwater - Wastewater that contains human waste (faeces and urine) and is considered a biological hazard.
- Coagulation - The process of adding a set of chemicals to water, which causes smaller contaminants (clay, silt or bacteria) to clump together, forming clusters known as 'Floc'.
- Desalination - The process of extracting fresh water from salt water.
- Disinfection - The removal of pathogens, such as bacteria, parasites and viruses, either using chemicals or UV light exposure.
- Drip irrigation - The process of water being directly applied to the plant's root zone through a network of pipes, providing a very low flow of water continuously to the plants.
- Effluent - Water that has undergone water treatment and is ready to be discharged into a waterway.
- Filtration - The process of removing suspended solids by passing water through a series of filters.
- Floc - Clusters of contaminants (clay, silt & bacteria) created during the coagulation process.
- Flocculation - The addition of long-chain polymers to stick the microscopic flocs together, making their removal easier.
- Greywater - Wastewater generated from household processes that do not involve faecal contamination or high-risk pathogens, e.g. bathwater.
- Pathogen - A microorganism, such as bacteria, parasites and viruses, which can cause illness.
- Purification - The process of removing undesirable chemicals, biological contaminants, and suspended solids from water to make it safe to drink.
- Screening - The process of using mesh filters to remove large pieces of debris (sticks, leaves, plastic waste, etc.) from water.
- Sedimentation - The process of leaving water undisturbed, allowing suspended solids to settle to the bottom of the tank as a sludge.
- Sewage liquor - The liquid part of the sewage after sedimentation, which goes on for biological processing.
- Sewage sludge - The semi-solid sediment formed in sewage treatment, consisting of a complex mixture of organic matter, microorganisms, and inorganic debris.
Sustainable Management of Water Resources : Desalination
Sustainable Management of Water Resources : Desalination
Over the past 100 years, water consumption has steadily risen due to increased demand for water both in people’s homes as well as demand for water for agriculture and industry. Treating water to make it potable (safe to drink) requires a significant amount of energy and other resources, and so people are being advised to reduce their water consumption where possible, to allow sustainable water management. This also applies to 'Water-Rich' countries like Scotland, but is especially critical in countries with limited fresh water supplies.
Over the past 100 years, water consumption has steadily risen due to increased demand for water both in people’s homes as well as demand for water for agriculture and industry. Treating water to make it potable (safe to drink) requires a significant amount of energy and other resources, and so people are being advised to reduce their water consumption where possible, to allow sustainable water management. This also applies to 'Water-Rich' countries like Scotland, but is especially critical in countries with limited fresh water supplies.
Given that ~ 97% of the water on Earth is saltwater, it would be great if humans could drink it, but unfortunately, drinking saltwater produces toxic effects in humans :
Given that ~ 97% of the water on Earth is saltwater, it would be great if humans could drink it, but unfortunately, drinking saltwater produces toxic effects in humans :
A major method that is used in over 170 countries to supplement their fresh water supplies is 'Desalination'. Desalination is the process of extracting fresh water from salt water. The source of the salt water is usually seawater, but the process is also used on brackish groundwater (less salty than seawater but still not drinkable), especially in the US, where there is a high proportion of salt deposits that the groundwater has passed through.
A major method that is used in over 170 countries to supplement their fresh water supplies is 'Desalination'. Desalination is the process of extracting fresh water from salt water. The source of the salt water is usually seawater, but the process is also used on brackish groundwater (less salty than seawater but still not drinkable), especially in the US, where there is a high proportion of salt deposits that the groundwater has passed through.
The map below shows the location of major desalination plants (over 10,000 m³/day) globally :
The map below shows the location of major desalination plants (over 10,000 m³/day) globally :
Desalination is only performed when absolutely necessary, as it is :
Desalination is only performed when absolutely necessary, as it is :
- Energy-intensive - The process involves creating mechanical pressure with electric pumps, requiring large amounts of electricity.
- Produces waste - The wastewater from the process is hyper-saline (more than twice as salty as seawater), which is then pumped back into the sea, causing environmental damage.
Sustainable Management of Water Resources : Water conservation
Sustainable Management of Water Resources : Water conservation
Water conservation aims to reduce the amount of water used in agriculture and industry. Depending on the level of development within a country, this will require different focuses.
Water conservation aims to reduce the amount of water used in agriculture and industry. Depending on the level of development within a country, this will require different focuses.
Less economically developed countries (LEDCs), such as Myanmar and Haiti, tend to use less water than more economically developed countries (MEDCs). The majority of water in LEDCs is used in agriculture for watering crops. LEDCs tend to be warmer countries, and as such, the water evaporates from the crops and the soil very quickly. Due to this, water must be continually applied to prevent the crops from dying.
Less economically developed countries (LEDCs), such as Myanmar and Haiti, tend to use less water than more economically developed countries (MEDCs). The majority of water in LEDCs is used in agriculture for watering crops. LEDCs tend to be warmer countries, and as such, the water evaporates from the crops and the soil very quickly. Due to this, water must be continually applied to prevent the crops from dying.
More economically developed countries (MEDCs), such as Japan and South Korea, tend to use a lower percentage of their water in the agricultural sector, but because of their larger and more advanced industrial and commercial sectors, much more water is used than in LEDCs.
More economically developed countries (MEDCs), such as Japan and South Korea, tend to use a lower percentage of their water in the agricultural sector, but because of their larger and more advanced industrial and commercial sectors, much more water is used than in LEDCs.
There is a range of methods of water conservation that can be used in an agricultural context :
There is a range of methods of water conservation that can be used in an agricultural context :
Drip Irrigation
Drip Irrigation
Unlike traditional flood or sprinkler irrigation, drip irrigation delivers water directly to the plant's root zone through a network of pipes, providing a very low flow of water continuously to the plants.
Unlike traditional flood or sprinkler irrigation, drip irrigation delivers water directly to the plant's root zone through a network of pipes, providing a very low flow of water continuously to the plants.
This method can reduce water usage by up to 70%.
This method can reduce water usage by up to 70%.
Drought-Resistant Crops
Drought-Resistant Crops
Drought-resistant crops can tolerate a reduction in water application while maintaining the same harvest yield as conventional varieties.
Drought-resistant crops can tolerate a reduction in water application while maintaining the same harvest yield as conventional varieties.
This method can reduce water usage by up to 30%.
This method can reduce water usage by up to 30%.
Conservation Tillage
Conservation Tillage
Tilling the soil exposes the moist lower layers to the air, causing rapid evaporation. Conservation tillage involves leaving the previous year’s crop residue (like stalks and leaves) on the ground, reducing this evaporation.
Tilling the soil exposes the moist lower layers to the air, causing rapid evaporation. Conservation tillage involves leaving the previous year’s crop residue (like stalks and leaves) on the ground, reducing this evaporation.
This method can reduce water usage by up to 15%.
This method can reduce water usage by up to 15%.
Use of Cover Crops
Use of Cover Crops
By planting a 'cover crop' (a plant grown for the benefit of the soil rather than for harvest), water loss is reduced as it creates a physical barrier against the sun and wind.
By planting a 'cover crop' (a plant grown for the benefit of the soil rather than for harvest), water loss is reduced as it creates a physical barrier against the sun and wind.
This method can reduce water usage by up to 15%.
This method can reduce water usage by up to 15%.
Tailwater Recovery
Tailwater Recovery
Tailwater is the water that has runoff a field. By the capture and reuse of this water, freshwater inputs can be reduced.
Tailwater is the water that has runoff a field. By the capture and reuse of this water, freshwater inputs can be reduced.
This method can reduce water usage by up to 30%.
This method can reduce water usage by up to 30%.
There is a range of methods of water conservation that can be used in an industrial context :
There is a range of methods of water conservation that can be used in an industrial context :
Closed-Loop Cooling
Closed-Loop Cooling
Traditional cooling systems pull from a source, use it once to absorb heat, and then discharge it back into the environment. A 'Closed-Loop' system recirculates the same water through a heat exchanger. The water is cooled (via fans or evaporation) and sent back through the machinery.
Traditional cooling systems pull from a source, use it once to absorb heat, and then discharge it back into the environment. A 'Closed-Loop' system recirculates the same water through a heat exchanger. The water is cooled (via fans or evaporation) and sent back through the machinery.
This method can reduce water usage by up to 98%.
This method can reduce water usage by up to 98%.
Wastewater Recycling
Wastewater Recycling
Wastewater recycling involves water being used multiple times for a range of tasks before being discharged. For example, the water used in fabric dyeing can be used through 10 cycles before it needs to be replaced.
Wastewater recycling involves water being used multiple times for a range of tasks before being discharged. For example, the water used in fabric dyeing can be used through 10 cycles before it needs to be replaced.
This method can reduce water usage by up to 70%.
This method can reduce water usage by up to 70%.
Leak Management
Leak Management
By detecting and repairing leaks within equipment and water supply systems, the overall water consumption can be reduced.
By detecting and repairing leaks within equipment and water supply systems, the overall water consumption can be reduced.
This method can reduce water usage by up to 30%.
This method can reduce water usage by up to 30%.
Smart Monitoring
Smart Monitoring
By monitoring the water flow through a system with a range of sensors, which detect micro-leaks, control flow rate to match usage and through A.I., predicting when components are about to fail before they do, water usage cna be reduced.
By monitoring the water flow through a system with a range of sensors, which detect micro-leaks, control flow rate to match usage and through A.I., predicting when components are about to fail before they do, water usage cna be reduced.
This method can reduce water usage by up to 30%.
This method can reduce water usage by up to 30%.
Production Changes
Production Changes
Changing procedures or methods of production can reduce water use. For example, moving from a batch to a continuous process reduces the number of 'wash-down' cycles required.
Changing procedures or methods of production can reduce water use. For example, moving from a batch to a continuous process reduces the number of 'wash-down' cycles required.
This method can reduce water usage by up to 25% on average, but some processes can be 100%.
This method can reduce water usage by up to 25% on average, but some processes can be 100%.
Improving Water Quality : Water Purification
Improving Water Quality : Water Purification
Water found naturally in the environment usually needs to be processed in some way before it is safe to drink.
Water found naturally in the environment usually needs to be processed in some way before it is safe to drink.
LEDCs obtain a lot of their drinking supplies from wells or open sources. This water can be full of bacteria and can cause disease. Water in LEDCs can also be obtained through rainwater harvesting, sub-surface dams, hand-dug wells and boreholes.
LEDCs obtain a lot of their drinking supplies from wells or open sources. This water can be full of bacteria and can cause disease. Water in LEDCs can also be obtained through rainwater harvesting, sub-surface dams, hand-dug wells and boreholes.
MEDCs, however, usually have more robust sanitation systems and water control regulations. Water is usually provided through a centralised 'mains water' system. This means that it is treated to prevent microbes or other contaminants and then piped directly to homes and businesses.
MEDCs, however, usually have more robust sanitation systems and water control regulations. Water is usually provided through a centralised 'mains water' system. This means that it is treated to prevent microbes or other contaminants and then piped directly to homes and businesses.
Water that has been extracted from aquifers, rivers or lakes will be purified before use at a water treatment plant :
Water that has been extracted from aquifers, rivers or lakes will be purified before use at a water treatment plant :
Water from a natural source, such as a reservoir or aquifer, is pumped into a water treatment plant. The water first passes through 'Screens', which remove large pieces of debris (sticks, leaves, plastic waste, etc.).
Water from a natural source, such as a reservoir or aquifer, is pumped into a water treatment plant. The water first passes through 'Screens', which remove large pieces of debris (sticks, leaves, plastic waste, etc.).
The water then undergoes a process of 'Coagulation' and 'Flocculation'. Coagulation is the process of adding a set of chemicals to the water, which causes smaller contaminants (clay, silt or bacteria) to clump together, forming clusters known as 'Floc'. Flocculation is the addition of long-chain polymers to stick the microscopic flocs together, making their removal easier.
The water then undergoes a process of 'Coagulation' and 'Flocculation'. Coagulation is the process of adding a set of chemicals to the water, which causes smaller contaminants (clay, silt or bacteria) to clump together, forming clusters known as 'Floc'. Flocculation is the addition of long-chain polymers to stick the microscopic flocs together, making their removal easier.
The next stage of the process is 'Sedimentation'. Sedimentation is a process where the water is left undisturbed, allowing the heavy flocs to settle to the bottom of the tank as a sludge, with the cleaner water then pumped off.
The next stage of the process is 'Sedimentation'. Sedimentation is a process where the water is left undisturbed, allowing the heavy flocs to settle to the bottom of the tank as a sludge, with the cleaner water then pumped off.
The final stage of the process is 'Filtration' and 'Disinfection'. Filtration removes remaining suspended solids by passing the water through a series of filters, whereas Disinfection removes pathogens, such as bacteria, parasites and viruses. The methods used for this depends of the relative wealth of the country.
The final stage of the process is 'Filtration' and 'Disinfection'. Filtration removes remaining suspended solids by passing the water through a series of filters, whereas Disinfection removes pathogens, such as bacteria, parasites and viruses. The methods used for this depends of the relative wealth of the country.
In LEDCs, this filtering is usually done using a low-speed, biological process, known as 'Slow Sand'. Water trickles through sand or ceramic filters at a very slow rate, allowing a 'bio-film' to grow on the filter, which consumes bacteria and viruses, removing pathogens without needing expensive chemicals.
In LEDCs, this filtering is usually done using a low-speed, biological process, known as 'Slow Sand'. Water trickles through sand or ceramic filters at a very slow rate, allowing a 'bio-film' to grow on the filter, which consumes bacteria and viruses, removing pathogens without needing expensive chemicals.
In MEDCs, this filtering is usually done using a high-speed, mechanical process, known as 'Rapid Sand'. The water passes through a sand and anthracite mix or through membrane filters. As the water moves rapidly, the filter materials cannot build up a biological layer to kill pathogens, so this process relies entirely on physical straining and added chemicals to remove pathogens.
In MEDCs, this filtering is usually done using a high-speed, mechanical process, known as 'Rapid Sand'. The water passes through a sand and anthracite mix or through membrane filters. As the water moves rapidly, the filter materials cannot build up a biological layer to kill pathogens, so this process relies entirely on physical straining and added chemicals to remove pathogens.
Due to this process of purification, water in most MEDCs is safe to drink straight from the tap :
Due to this process of purification, water in most MEDCs is safe to drink straight from the tap :
Improving Water Quality : Sewage Treatment
Improving Water Quality : Sewage Treatment
Wastewater is water that remains at the end of a range of processes; domestic, industrial, or commercial activities, and can be split into two types :
Wastewater is water that remains at the end of a range of processes; domestic, industrial, or commercial activities, and can be split into two types :
- Greywater - Wastewater generated from processes that do not involve faecal contamination or high-risk pathogens, e.g. bathwater, water from washing machines, etc. Greywater can usually be reused for some processes, with minimal further processing.
- Blackwater - Wastewater that contains human waste (faeces and urine) and is considered a biological hazard. Blackwater requires extensive processing to make it safe.
In Scotland, wastewater is carried from homes and businesses to water treatment plants through a network of combined sewers. A combined sewer is a series of drains and pipes that carry both wastewater and surface water (rainfall, drains, etc.).
In Scotland, wastewater is carried from homes and businesses to water treatment plants through a network of combined sewers. A combined sewer is a series of drains and pipes that carry both wastewater and surface water (rainfall, drains, etc.).
The diagram below shows how a combined sewer system works in clear weather, rain and then prolonged storm conditions :
The diagram below shows how a combined sewer system works in clear weather, rain and then prolonged storm conditions :
This system is designed such that any overflow from the drain or storm tanks is diluted as much as possible to reduce the impact of the sewage discharge on rivers or the sea. The Scottish Environmental Protection Agency (SEPA) monitors the discharge of pollution into Scotland's rivers and sea, and has the power to fine companies who break the rules on levels of pollution.
This system is designed such that any overflow from the drain or storm tanks is diluted as much as possible to reduce the impact of the sewage discharge on rivers or the sea. The Scottish Environmental Protection Agency (SEPA) monitors the discharge of pollution into Scotland's rivers and sea, and has the power to fine companies who break the rules on levels of pollution.
The video below shows a BBC news story covering the release of raw sewage into waterways in England :
The video below shows a BBC news story covering the release of raw sewage into waterways in England :
Water that has passed through the sewer system will be processed at a water treatment plant before being discharged into a river or the sea :
Water that has passed through the sewer system will be processed at a water treatment plant before being discharged into a river or the sea :
Water and sewage from the sewer system are pumped into a sewage treatment plant. The sewage undergoes three stages of processing :
Water and sewage from the sewer system are pumped into a sewage treatment plant. The sewage undergoes three stages of processing :
Primary Treatment (Physical) - The sewage first passes through 'Screens', which remove large pieces of debris (sticks, leaves, plastic waste, etc.). The sewage then undergoes sedimentation to remove any remaining solids. The cleaner water, known as 'liquor', is pumped out and passes to the next stage, with the 'sludge' (the sediment at the bottom of the tank) being removed for further processing.
Primary Treatment (Physical) - The sewage first passes through 'Screens', which remove large pieces of debris (sticks, leaves, plastic waste, etc.). The sewage then undergoes sedimentation to remove any remaining solids. The cleaner water, known as 'liquor', is pumped out and passes to the next stage, with the 'sludge' (the sediment at the bottom of the tank) being removed for further processing.
Secondary Treatment (Biological) - The liquor passes into an aeration tank, where bubbles are used to agitate the liquor and provide oxygen for a range of microorganisms. These microorganisms 'eat' the organic waste, converting it into new bacterial biomass, in a process known as 'Biological oxidation'. This produces more sludge, which is again removed for processing.
Secondary Treatment (Biological) - The liquor passes into an aeration tank, where bubbles are used to agitate the liquor and provide oxygen for a range of microorganisms. These microorganisms 'eat' the organic waste, converting it into new bacterial biomass, in a process known as 'Biological oxidation'. This produces more sludge, which is again removed for processing.
Tertiary Treatment (Chemical) - The liquor then undergoes a final filtering process to remove any remaining suspended matter, and is chemically treated to remove pathogens, at which point it is known as 'effluent'. This effluent is then discharged into a river or the sea.
Tertiary Treatment (Chemical) - The liquor then undergoes a final filtering process to remove any remaining suspended matter, and is chemically treated to remove pathogens, at which point it is known as 'effluent'. This effluent is then discharged into a river or the sea.
The sludge which was extracted is then further processed for a variety of uses :
The sludge which was extracted is then further processed for a variety of uses :
Fertiliser
Fertiliser
The sludge is heat-treated to remove pathogens, condensed and solidified to produce 'biosolid' fertiliser. This can then be applied to agricultural fields.
The sludge is heat-treated to remove pathogens, condensed and solidified to produce 'biosolid' fertiliser. This can then be applied to agricultural fields.
This is strictly regulated to prevent contamination of fields or waterways by pollutants found in the original sewage.
This is strictly regulated to prevent contamination of fields or waterways by pollutants found in the original sewage.
Incineration
Incineration
The sludge can be dried, forming a solid 'sludge cake' which can be burned in an incinerator to generate electricty.
The sludge can be dried, forming a solid 'sludge cake' which can be burned in an incinerator to generate electricty.
Biogas
Biogas
Biogas is the flammable gas methane, created by the anaerobic (without oxygen) digestion of the sludge. This biogas can then be burned, with the heat energy used to generate electricity or heat for other uses.
Biogas is the flammable gas methane, created by the anaerobic (without oxygen) digestion of the sludge. This biogas can then be burned, with the heat energy used to generate electricity or heat for other uses.
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