The 3 Step Sewage Treatment Process
Sewage treatment is the process in which contaminants are removed from municipal wastewater. This wastewater mainly contains household sewage but may also contain small amounts of industrial wastewater too. Many different processes are taken place to produce treated wastewater and can be broken down into three main steps, primary, secondary and tertiary.
Although there are three main steps, there is also something important that happens before these can even begin. This is called the pre-treatment stage, this consists of materials being removed from the wastewater which would have damaged or clogged the pipes. Objects that are commonly removed during this process are sanitary products, nappies, plastic, leaves and other large objects.
In the first of the three steps, the goal is to separate the organic matter and sludge from the rest of the water. This is done by having the wastewater flow through large settlement tanks where the solids will sink to the bottom and the grease and oils rise. The oils and grease are usually skimmed off the top of the surface and the sludge will be gathered to the centre of the floor by large scrapers. From there it is then pumped away as the rest of the water moves onto the secondary treatment.
At this stage, there may still be sludge floating found in the water that didn’t settle to the base during the primary treatment. At this point, the water is in rectangular tanks called aeration lanes during which air will be pumped into the water. This encourages the bacteria to break down the small bits of sludge that escaped. The more this happens, the more the good bacteria will multiply and take over.
The purpose of this final stage is to further improve the quality of the water before it is released and reused in the environment for lakes, rivers, seas or other places. This treatment involves filtering the water to remove any inorganic substances such as nitrogen and phosphorus, as well as any viruses or bacteria that could be harmful to humans.
After all the treatments, the wastewater is finally clean, meaning it can return to the environment. The quality of the water is reviewed and regulated by the Environmental Agency to make sure it is up to standards before this happens.
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