Wastewater treatment is very essential to any modern civilization given that all water is essentially recycled, be it from a toilet or a bathtub drain. We all see the huge water towers alongside roads and highways, but few people really know how the treatment process works. We don’t really think about it because no one wants to dwell on the fact that their drinking water may have seen the inside of a toilet bowl. The following article will explain step by step how sewage is able to go from toilet water to drinkable tap water, and used all over again.
Pre-Treatment
This is the process by which all obvious particles are removed from the water. First, a large screen or rake is used to remove any large floating objects, such as sticks or plastic. Next, a settling chamber removes the smaller particles. It is basically just a tank where the water sits long enough to let all the particles settle to the bottom and allow the liquid to be removed. The final step in this process is to remove fat and grease with a large skimmer, since these substances will always float to the surface.
Primary Treatment
This is very similar to the previous step, just more thorough. Water is passed through various chambers to allow any remaining sludge to settle, and more grease and fat is skimmed off as it goes along. Mechanical scrapers collect the waste and move it to another facility, where it too can be recycled and the grease used to make soap in a process called saponification.
Secondary Treatment
In this stage, the focus is on degrading any biological products, such as human waste, soap, and detergent. This normally is done by introducing bacteria into the water which will degrade some of the material, and make the rest clump together in masses known as floc. This is done in one of two ways. The bacteria can be introduced directly into the sewage and mixed in, or the sewage can be continually trickled over a filter the bacteria is growing on. The former is more space efficient but less capable of handling heavily contaminated loads. After this process is completed the resulting mixture goes to another settling tank to once again allow the chunks to settle to the bottom and be removed.
Tertiary Treatment
This is the final cleansing stage. During this part, the water is run through sand to remove the last remnants of suspended material, and over a carbon filter to remove remaining toxins. Some plants also use a process called lagooning, in which man made lagoons provide a final area for sediment to settle, and for further microbes to remove any remaining harmful particles. After everything is removed, the final step is to disinfect it. The most common way is by using chlorine, but other methods include ultraviolet light and generated ozone.
Of course, after all this wastewater treatment is completed, it still does not go right to your tap. This water is clean, and is released back into the environment, but plants that create drinking water have even further steps once they take the water back from the environment.
Credit: Source by Adriana Noton
