Types of wastewater treatment

First, the wastewater is collected by a series of collecting tubes that send them to the water purification stations (EDAR) where they will submit them to the different treatments to purify them. In these stations they usually remain an average of 24-48 h before they are returned to its receiving channel, either a river, a reservoir or even the sea. Once they enter the EDAR, they are subjected to:

• PRETRATATIONwhich consists in the elimination of larger solids such as sands and oils.
• Primary treatment.
• Secondary treatmentin the event that you want to further purify water
• Finally a Tertiary treatment When the waters are poured into protected spaces, since due to the cost it has it does not usually do normally. Next, these treatments are explained.

The primary treatment consists of a set of physical-chemical processes that apply to Reduce the content of water suspension of water. These suspended solids can be sedimentable or floating. The former are able to reach the bottom after a short period of time while the latter are formed by very small particles (less than 10 microns) integrated into the water, so they are not able to float or sediment and to eliminate them, other techniques are required.

Some of the Resiudal water purification methods are the following:

• Sedimentation: process by which the particles fall to the background thanks to the action of gravity. They can eliminate up to 40% of the solids containing the waters. This process occurs in tanks called decanters.
• Floatation: It consists of the removal of foams, fats and oils since due to the low density they have they are in the surface layer of the water. Low density particles can also be eliminated, for which air bubbles are injected by facilitating their ascension. With flotation, up to 75% of suspended particles could be eliminated. This occurs in other tanks called dissolved air floats.
• Neutralization: It consists of pH standardization, that is, adjust it to a value in the range of 6-8.5, which is typically the value of water. In the case of acid wastewater (low pH) such as those containing heavy metals, alkaline substances (high pH) are added to raise the pH of the water. On the contrary, in alkaline wastewater CO2 is usually introduced so that the water pH decreases to normal values.
• Other processes: To achieve greater purification of wastewater, other techniques such as the use of septic tanks, lagooning, green filters or other chemical processes (ion exchange, oxidation, reduction, etc.) can be applied.

Secondary treatment consists of a set of biological processes that claim eliminate organic matter that are in wastewater. These biological processes consist of the work carried out by some bacteria and microorganisms and that is based on the transformation of organic matter into cell biomass, energy, gases and water. This treatment has an efficacy of 90%.

Several processes, aerobes and anaerobes can be distinguished:

• The Aerobic processes They are performed in the presence of oxygen, so it is necessary to introduce it in the tanks where the wastewater is. At this stage, part of the degradation of organic matter occurs, from which water and CO2 follow, and also the elimination of nitrogen products. Ammonium, derived from very toxic nitrogen, is transformed into nitrate into a reaction called nitrification. However, nitrate, although it is no longer toxic is an assimilable form of nitrogen and, therefore, could cause an algae proliferation and water nutrients in the receiving medium (eutrophication), so through denitrification it becomes nitrogen and is released to the atmosphere.
• On the contrary, the anaerobic processes They are performed in the absence of oxygen. In this process, fermentative reactions occur in which organic matter is transformed into energy, methane and carbon dioxide.

Next, some are mentioned wastewater purification methods:

• Active sludge: It is an aerobic process that consists of adding floccles or lumps of organic matter with microorganisms to the wastewater and constantly infiltrating oxygen so that the reactions occur.
• Bacterial beds: aerobic process These are supports where microorganisms are located and wastewater is thrown in a few amounts to maintain aerobic conditions.
• FGreen Istros: These are crops that are irrigated with wastewater since they have the ability to absorb their compounds.
• Anaerobic digestion: It is an anaerobic process that is carried out in completely closed tanks. Mainly bacteria that produce acid and methane are used when they degrade organic matter.
• Others: Biodisco, biocylinders, electrocoagulation, electrooxidation, biological membrane reactor, and so on.

Tertiary treatment consists mainly in the Elimination of pathogensespecially fecal bacteria and nutrients. This treatment is optional and normally done when water is going to be reused, such as gardens or other public spaces so that they do not involve a danger to human health, or in the event that the receptor channels are in protected spaces or with high quality in their waters. The Wastewater treatment processes more common are the following:

• Ultraviolet Radiation: In order to apply the waters must be very clear and without much dissolved particulate material so that the light can reach everywhere. Ultraviolet radiation prevents the reproduction of microorganisms and prevents them from developing their ability to infection. It is able to eliminate 99% of microorganisms.
• Ion exchange: Technique used to withdraw salts in low concentrations and for this resins are used that are capable of retaining ions temporarily.
• Inverse osmosis: It consists of the elimination of salts when passing the water from a more concentrated solution to a more diluted.
• Filtration: It consists of the elimination of organic particles that could not be extracted in the previous treatments. For this, sands and gravels are used.
• Chlorination: It consists of the elimination of microorganisms through the application of chlorinated products. In addition, they contribute to the elimination of ammonium and prevents the oxidation of inorganic elements.

This is a small part of the processes that are usually used in purifying plants, but currently they are investigating new techniques so that the purification of the waters is cheaper and more complete. In addition, everything explained in this article focuses on the water line of the treatment plants, in parallel there is a sludge line in which the solid waste that is extracted from wastewater is purified and purified.

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