Before raw sewage can be safely released back into the environment, it needs to be treated correctly in a water treatment plant. In a water treatment plant, sewage goes through a number of chambers and chemical processes to reduce the amount and toxicity of the waste.
The sewage first goes through a primary phase. This is where some of the suspended, solid particles and inorganic material is removed by the use of filters.
The secondary phase of the treatment involves the reduction of organic, this is done with the use of biological filters and processes that naturally degrade the organic waste material.
The final stage of treatment is the tertiary phase; this stage must be done before the water can be reused. Almost all solid particles are removed from the water and chemical additives are supplied to get rid of any left-over impurities.
Septic tanks treat sewage at the place where it is located, rather than transporting the waste through a treatment plant or sewage system. Septic tanks are usually used to treat sewage from an individual building.
Untreated sewage from a property flows into the septic tank and the solids are separated from the liquid.
Solid material is separated depending on their density. Heavier particles settle at the bottom of the tank whereas lighter particles, such as soap scum, will form a layer at the top of the tank.
Biological processes are used to help degrade the solid materials.
The liquid then flows out of the tank into a land drainage system and the remaining solids are filtered out.
Denitrification is an ecological approach that can be used to prevent the leaching of nitrates in soil, this in turn stops any ground water from being contaminated with nutrients.
Fertilisers contain nitrogen, and are often applied to crops by farmers to help plant growth and increase the yield.
Bacteria in the soil convert the nitrogen in the fertilizer to nitrates, making it easier for the plants to absorb.
Immobilization is a process where the nitrates become part of the soil organic matter.
When oxygen levels are low, another form of bacteria then turns the nitrates into gases such as nitrogen, nitrous oxide and nitrogen dioxide.
The conversion of these nitrates into gas is called denitrification. This prevents nitrates from leaching into the soil and contaminating groundwater.
Ozone wastewater treatment is a method that is increasing in popularity. An ozone generator is used to break down pollutants in the water source.
The generators convert oxygen into ozone by using ultraviolet radiation or by an electric discharge field.
Ozone is a very reactive gas that can oxidise bacteria, moulds, organic material and other pollutants found in water.
Using ozone to treat wastewater has many benefits:
Kills bacteria effectively.
Oxidises substances such as iron and sulphur so that they can be filtered out of the solution.
There are no nasty odours or residues produced from the treatment.
Ozone converts back into oxygen quickly, and leaves no trace once it has been used.
The disadvantages of using ozone as a treatment for wastewater are:
The treatment requires energy in the form of electricity; this can cost money and cannot work when the power is lost.
The treatment cannot remove dissolved minerals and salts.
Ozone treatment can sometimes produce by-products such as bromate that can harm human health if they are not controlled.
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