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Wastewater is those resulting from human activities, comes from cities, industries, and so on. These wastewater pose a potential danger to the environment as any spill or leak would release toxic substances into the environment and trigger ecological disasters. In order for these waters to return to the natural environment, they must follow a series of treatments that consist of eliminating their waste. These treatments depend on the characteristics of the wastewater and its final destination. If you are interested in this topic, keep reading because here in Green Ecology we are going to explain what the types of wastewater treatment.
Types of visual water treatment processes
First, the wastewater is collected by a series of collector tubes that make it reach the Water Treatment Stations (WWTP) where it will be subjected to different treatments to purify it. In these stations they usually stay an average of 24-48 hours before being returned to their receiving channel, either a river, a reservoir or even the sea. Once they enter the WWTP, they are subjected to:
- Pretreatment, which consists of the elimination of the largest solids such as sand and oils.
- Primary treatment.
- Secondary treatment, in the event that you want to further purify the water
- Finally a tertiary treatment when the waters are discharged to protected areas, since due to the cost it has, it is not usually done normally. These treatments are explained below.
Wastewater treatment: primary
The primary treatment consists of a set of physical-chemical processes that are applied to reduce the content of suspended particles in the water. These suspended solids can be sedimentable or floating. The former are capable of reaching the bottom after a short period of time, while the latter are made up of very small particles (less than 10 microns) integrated in the water so they are not able to float or settle and to remove them requires other techniques.
Some of the sewage treatment methods are as follows:
- Sedimentation: process by which the particles fall to the bottom thanks to the action of gravity. Up to 40% of the solids contained in the water can be removed. This process occurs in tanks called decanters.
- Floatation: It consists of the removal of foams, fats and oils since, due to their low density, they are located in the surface layer of the water. Low density particles can also be removed, for which air bubbles are injected facilitating their ascent. With flotation, up to 75% of suspended particles could be removed. This occurs in other tanks called dissolved air floats.
- Neutralization: It consists of normalizing the pH, that is, adjusting it to a value in the range of 6-8.5, which is typically the value of water. In the case of acidic 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 pH of the water falls to normal values.
- Other processes: To achieve greater purification of wastewater, other techniques such as the use of septic tanks, lagoons, green filters or other chemical processes (ion exchange, oxidation, reduction, etc.) can be applied.
Secondary wastewater treatment
Secondary treatment consists of a set of biological processes that seek to remove organic matter that is in the sewage. These biological processes consist of the work carried out by some bacteria and microorganisms and which is based on the transformation of organic matter into cellular biomass, energy, gases and water. This treatment is 90% effective.
Several processes can be distinguished, aerobic and anaerobic:
- The aerobic processes They are carried out in the presence of oxygen, so it is necessary to introduce it into the tanks where the wastewater is. In this stage, part of the degradation of organic matter occurs, from which water and CO2 are released, as well as the elimination of nitrogenous products. Ammonia, derived from very toxic nitrogen, is transformed into nitrate in a reaction called nitrification. However, nitrate, although it is no longer toxic, is an assimilable form of nitrogen and, therefore, could cause a proliferation of algae and the enrichment of nutrients in the waters in the receiving environment (eutrophication), so through denitrification This is converted into nitrogen and released into the atmosphere.
- On the contrary, anaerobic processes they are carried out in the absence of oxygen. In this process fermentative reactions occur in which organic matter is transformed into energy, methane and carbon dioxide.
Here are some sewage treatment methods:
- Active sludge: It is an aerobic process that consists of adding flocs or lumps of organic matter with microorganisms to the wastewater and constantly infiltrating oxygen so that the reactions take place.
- Bacterial beds: aerobic process. These are supports where microorganisms are found and residual water is poured in small quantities to maintain aerobic conditions.
- Fgreen filters: These are crops that are irrigated with wastewater since these have the ability to absorb their compounds.
- Anaerobic digestion: It is an anaerobic process that takes place in completely closed tanks. Bacteria that produce acid and methane are mainly used when they degrade organic matter.
- Others: biodisks, biocylinders, electrocoagulation, electrooxidation, membrane bioreactor, and so on.
Tertiary wastewater treatment
Tertiary treatment consists mainly of elimination of pathogens, especially fecal bacteria and nutrients. This treatment is optional and is normally done when the water is going to be reused, such as in gardens or other public spaces so that they do not pose a danger to human health, or in the event that the receiving channels are in spaces protected or with a high quality in its waters. The wastewater treatment processes The most common are the following:
- Ultraviolet radiation: In order to be applied, the waters must be very clear and without much dissolved particulate matter so that the light can reach everywhere. Ultraviolet radiation prevents the reproduction of microorganisms and prevents them from developing their infectious capacity. It is capable of eliminating around 99% of microorganisms.
- Ion exchange: Technique used to remove salts in low concentrations and for this, resins that are capable of temporarily retaining ions are used.
- Inverse osmosis: It consists of the elimination of salts when the water passes from a more concentrated solution to a more dilute one.
- Filtration: It consists of the elimination of organic particles that have not been able to be extracted in the previous treatments. Sand and gravel are used for this.
- Chlorination: It consists of the elimination of microorganisms through the application of chlorinated products. In addition, they contribute to the elimination of ammonia and prevent the oxidation of inorganic elements.
This is a small part of the processes that are commonly used in treatment plants, but they are currently being researching new techniques so that water purification 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 the wastewater is treated and purified.
If you want to read more articles similar to Types of wastewater treatment, we recommend that you enter our Recycling and waste management category.
