Most human activities use water in their processes. During the process, physical, chemical and biological changes occur in the natural characteristics of the water, generating the contaminated wastewater from the process, known as effluent.
What happens to this process waste water?
The effluent will always return to the spring from which it was taken (The receiving source). However, because it has been subjected to the stages resulting from a specific type of use, wastewater ends up having different characteristics from those that were intrinsic to it at the time of its capture, and its contact with the water body can significantly compromise the quality of the water in the source. The impairment of the water quality of a body of water can also be referred to as "water pollution".
Consequences of water pollution
The main sources of water pollution are domestic and industrial effluents. They can reach the watercourse in the following ways:
(i) through surface runoff and/or infiltration into the ground. This is known as "diffuse" contamination;
(ii) through sewage outfall pipes and rainwater galleries. In this case, it is called "point source" contamination. Whether diffuse or point source, when effluents come into contact with the receiving body, they tend to modify the original composition of the water, making it potentially harmful to aquatic life. Furthermore, after this contact, the water in the receiving body may even become unsuitable for a certain use that was previously established for it.
Main impacts of effluent on water
The impacts of water pollution are diverse, affecting, for example, the color of the water, contamination by microorganisms and/or toxic compounds, changes in oxygen consumption and biochemical oxygen demand, etc.
Every body of water has a natural capacity for "recovery", which is known as "self-depuration". However, depending on the amount of discharges into the water, the source loses this "self-sufficiency". This can be seen in the following figures. It shows the growth of cities and, with it, the increase in discharges into the receiving body.
With the growth of residential and industrial areas, there is a significant increase in discharges into the water body, preventing the process of "self depuration".
When the river's natural capacity is no longer sufficient, this corroborates the idea that it is necessary to "adjust" the effluent before it is discharged into the receiving body. This action ensures that, even after the effluent has been discharged, the water quality of the source is not compromised. This process is called "Effluent Treatment".
The definition of the treatment to which the effluent should be subjected will depend on the origin of the wastewater (whether domestic or industrial - including considering the type of industry to which it refers). The treatment of this wastewater, however, must have an objective. It must reach a defined standard; a limit. And to guide this process, there are legal instruments that set out the minimum characteristics that an effluent must have in order to be discharged into the source without causing damage to the water quality of the receiving body.
What are the types of effluent?
There are two types of effluent: domestic and industrial. The specific characteristics of each can be seen below.
Domestic effluent
A particular type of water becomes a domestic effluent when, during its passage through the sanitary facilities, it ends up incorporating new components into its initial condition. Sewage is generated from the use of toilets, drains, sinks, washbasins, urinals, etc., and in order to understand what the discharge of this type of effluent generates in the environment, it is necessary to know its characteristics more specifically.
Generally speaking, the main characteristics of domestic effluents are:
- High levels of solids and nutrients (organic matter)
- High levels of Coliform bacteria
- High Biochemical Oxygen Demand
Industrial effluent
A water becomes an industrial effluent when, during its participation in different production processes, it ends up incorporating new components into its initial condition. The effluents generated from industrial activity can have a huge variety of characteristics, considering the number of possible processes that can be carried out. In this sense, it is extremely necessary to understand the characteristics of the effluent before it is returned to the environment.
Industrial activity makes use of components that are potentially aggressive to the environment, the main characteristics being the existence of organic compounds, radioactive substances, acids and heavy metals in their composition.
Knowledge of the composition of the effluent is fundamental, since at some point it will be discharged into the receiving body. In other words, it will be discharged back into the body of water from which it was abstracted before it was used and modified. Depending on the composition of this effluent, it can cause changes to ecosystems, which is why effluent management is so important. It is essential that the characteristics of the wastewater do not compromise the water quality of the source to which it is destined.
Regardless of the water body's self-depuration capacity, depending on the amount of material discharged, it can "overload" the receiving body, meaning that this recovery capacity alone is not enough to prevent degradation of the water in the source.
For this reason, there are legal instruments (laws, decrees, resolutions) that indicate the characteristics that domestic effluents must have when discharged into a given source. Based on these instruments, the effluent to be discharged must be adapted to the receiving body, using specific treatments.
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