Domestic sewage is made up of all the water and waste that it carries through the plumbing of houses, offices and commercial establishments. In other words, it can be said that it is all the garbage we produce using water, which goes down all the sinks and toilets, in addition to the shower and drains scattered throughout the house. Rainwater flowing down sidewalks and gutters is also mixed in sewage networks.
But where does all this sewage go? Unfortunately, most of it is not treated and ends up being deposited in rivers and seas. In Brazil, 49% of sewage is collected by treatment networks, but only 10% of all sewage produced is, in fact, treated.
Treatment is carried out at Sewage Treatment Plants (ETE). These places are able, through chemical and biological decomposition processes, imposed by the health standard of CONAMA Resolution No. 357/2005, to treat sewage.
Sewage is basically made up of 99.9% water, 0.1% solids and numerous living organisms, such as bacteria, viruses, worms and protozoa, which are released along with human waste. Even so, sewage decomposition is a process that requires several days and, therefore, a relatively expensive process, with an investment of 0.04% of the national GDP of the Federal Government.
The treatment of domestic sewage is also very important for the preservation of the environment. Sewage contaminates rivers, lakes, dams and seas because they have excess sediments and microorganisms that can cause diseases, such as schistosomiasis, leptospirosis, cholera and pyoderma.
Thus, it can transform nearby areas, unbalancing the region’s ecosystem. Rivers and beaches undergo silting up process, which is nothing more than the increase of sediments (solids) at its base, causing an increase in the water level and, consequently, floods. Sewage can also contaminate water sources and places that serve as a source of drinking water for the population. The most affected are the fish, whole species can be extinct from the place where the domestic sewage is thrown. Besides them, aquatic and riverside vegetation may end up dying. The stench is also a dangerous consequence of domestic sewage thrown into the wild.