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C10 E) Waste Water Treatment
C10 E) Waste Water Treatment
Sewage is wet waste from homes and industry. Developed nations tend to have two sewage networks; one is for dealing with household wet waste and the other is for dealing with industrial wet waste. There are two sewage systems because the type of wet waste that is produced by households and industry is different. Household sewage is any water that goes down the drain; it will come from the showers, toilets, sinks when we wash up or wash our hands etc…. Household sewage will contain waste water, urine & faeces and chemicals from soaps & detergents (may be organic or inorganic, and soluble or insoluble chemicals). Industrial sewage tends to contain more chemicals than household sewage. Industrial sewage includes waste water from agriculture, which can contain high quantities of nutrient from fields because of the fertilisers that are sprayed on fields and slurry from farm animals (slurry is a mixture of manure and water).
Domestic sewage and industrial sewage must be treated before it enters the waterways (such as a river or the sea). This is so that organic matter, chemicals and harmful pathogens do not enter the water ways where they may potentially kill organisms and interfere/ destroy an ecosystem.
Domestic sewage and industrial sewage must be treated before it enters the waterways (such as a river or the sea). This is so that organic matter, chemicals and harmful pathogens do not enter the water ways where they may potentially kill organisms and interfere/ destroy an ecosystem.
Treating Sewage
There are a few different methods of treating sewage to make it safe to release into water ways. Here is one of the processes used to treat household sewage.
There are a few different methods of treating sewage to make it safe to release into water ways. Here is one of the processes used to treat household sewage.
The sewage is first passed through a screen which removes grit and large objects like twigs and rubbish (like plastic bags or crisp packets).
The sewage then sits in settling tanks. The solids in the sewage sink towards the bottom of the settling tank and they are known as sludge. The water that remains at the top of the settling tank is known as effluent. The process in the settling tanks is known as sedimentation. The sludge and effluent take two different treatment journeys.
The effluent passes through an aeration tank that contains bacteria. The bacteria break down all of the organic matter in the effluent. Air is pumped through the aeration tank so that there is plenty of oxygen for the bacteria to aerobically respire; the bacteria aerobically digest the organic matter in the effluent. The effluent after the aeration tank contains less organic matter and fewer pathogens, which means that it is now safe to be released into the water ways (rivers or the sea).
The sludge passes onto a separate tank that is sealed, which means that there will be very little or no oxygen present in the tank. The tank contains bacteria that breakdown the organic matter in the sludge. As there is no oxygen present in the tank, the bacteria break down the organic material by anaerobic digestion (digestion without oxygen being present). The breaking down of sludge by the bacteria produces methane gas (natural gas), which can be used as an energy source (e.g. the fuel used in a gas hob/ gas heating system in a home). After the sludge has been broken down, the remaining waste can be used as a fertiliser because it has very high concentrations of nutrient; the waste is sprayed onto crops in fields.
There will be a few additional steps in the treatment process if the sewage contains toxic chemicals, which may be the case if the sewage has come from industry. If the sewage contains toxic chemicals, the treatment plant will either add chemicals, use membranes or use ultraviolet light to make the effluent and sludge safe to be disposed of in water ways.
The sewage then sits in settling tanks. The solids in the sewage sink towards the bottom of the settling tank and they are known as sludge. The water that remains at the top of the settling tank is known as effluent. The process in the settling tanks is known as sedimentation. The sludge and effluent take two different treatment journeys.
The effluent passes through an aeration tank that contains bacteria. The bacteria break down all of the organic matter in the effluent. Air is pumped through the aeration tank so that there is plenty of oxygen for the bacteria to aerobically respire; the bacteria aerobically digest the organic matter in the effluent. The effluent after the aeration tank contains less organic matter and fewer pathogens, which means that it is now safe to be released into the water ways (rivers or the sea).
The sludge passes onto a separate tank that is sealed, which means that there will be very little or no oxygen present in the tank. The tank contains bacteria that breakdown the organic matter in the sludge. As there is no oxygen present in the tank, the bacteria break down the organic material by anaerobic digestion (digestion without oxygen being present). The breaking down of sludge by the bacteria produces methane gas (natural gas), which can be used as an energy source (e.g. the fuel used in a gas hob/ gas heating system in a home). After the sludge has been broken down, the remaining waste can be used as a fertiliser because it has very high concentrations of nutrient; the waste is sprayed onto crops in fields.
There will be a few additional steps in the treatment process if the sewage contains toxic chemicals, which may be the case if the sewage has come from industry. If the sewage contains toxic chemicals, the treatment plant will either add chemicals, use membranes or use ultraviolet light to make the effluent and sludge safe to be disposed of in water ways.
Obtaining Drinking Water from Sewage
We can obtain potable water (drinking water) from sewage. However, the process of obtaining potable water from sewage uses more energy and is more expensive than obtaining potable water from freshwater. But, obtaining potable water from sewage is cheaper than obtaining potable water from the desalination of sea water/ saltwater (either distillation or reverse osmosis).
We can obtain potable water (drinking water) from sewage. However, the process of obtaining potable water from sewage uses more energy and is more expensive than obtaining potable water from freshwater. But, obtaining potable water from sewage is cheaper than obtaining potable water from the desalination of sea water/ saltwater (either distillation or reverse osmosis).