The water that has been used and has not been treated before releasing it into another water body is known as wastewater. This wastewater needs to be treated to prevent water pollution. There are various sources of wastewater. From the water that is flushed down the toilet to the water that is rinsed down the drain, everything is wastewater. Even rainwater and runoff get washed down the street gutters and eventually end up in the wastewater treatment plant. Even the runoff from industrial and agricultural waste is known as wastewater and needs to go through the water treatment companies.
Across the world, two out of the ten people do not have access to safe drinking water and in many states across the globe, there are situations of drought and acute water scarcity. Robert Glennon in his book, Unquenchable: America’s Water Crisis and What to do about it?, has reported that approximately 5.8 billion gallons of water are flushed down the drains of America every day. There are water treatment companies who treat this wastewater to turn them into safe drinking water. In fact, the federal governments of various states are assigned with the task of wastewater treatment to ensure there is enough safe drinking water.
How is wastewater treated?
The water treatment companies make sure that the wastewater goes through various levels of treatment—primary, secondary and tertiary treatment. The municipal wastewater treatment systems usually use the primary and secondary levels of treatment. Some also use the tertiary level of treatment. The order of treatment may vary from one plant to another.
In the primary level of treatment, screens and settling tanks are used to remove the majority of solid waste. 35% of water pollutants are comprised of these solid particles and hence screening these out in water treatment is very important. The materials screened out in the settling tanks and screens are then put in the landfills for decomposition. After screening out, the water is put through settling tanks for hours to remove the sludge and slime.
In the secondary level of treatment, bacteria are used to digest the remaining pollutants in water. This is done by mixing the wastewater with bacteria and oxygen. Oxygen is used to help the bacteria digest the pollutants faster. Again, the water is put in settling tanks to further remove the sludge. After this treatment, the water is almost 90% to 95% free of pollutants. After this further chlorine, ultraviolet light and ozone are used to further clean the water. This water is then sent to various plants to be circulated as clean drinking water.
In the tertiary level of treatment dissolved particles such as chemicals, metals and colour are removed. There are a number of physical and biological treatment processes that are carried out to remove all kinds of impurities. To remove biological pollutants a method called Biological Nutrient Removal is used to remove all impurities. All these processes ensure that water is completely pollutant free and suitable for safe drinking.