All human activities generate wastewater that must be treated. Wastewater treatment plants (WWTPs) are responsible for treating this water, which comes from urban, industrial and agricultural activities. This treatment is essential to protect the environment, since the discharge of untreated wastewater can release toxic substances that damage ecosystems, contaminate water sources and cause ecological disasters. Adequate water treatment is key to preserving water resources and ensuring environmental sustainability.
Today we are going to delve into what water treatment plants are, how they work, the different treatment processes they carry out and the advantages they provide.
What are sewage treatment plants and how do they work?
A Wastewater Treatment Plant (WWTP) is an industrial facility that treats dirty (waste) water to remove the contaminants present in it. Wastewater comes from various sources: urban, industrial and agricultural. The purification process allows treated water to be returned to natural waterways such as rivers, seas or lakes, safely, without negatively impacting the environment. Wastewater treatment plants also play a key role in the reuse of water for agricultural or industrial purposes, thus contributing to the saving of such a necessary resource.
The operation of these plants is based on dividing the treatment into several phases. Depending on the level of purification required, the water can go from a basic treatment to an advanced treatment, known as tertiary treatment, which makes it suitable even for reuse in certain human processes.
Let's analyze in detail the phases of wastewater treatment in a WWTP.
Water treatment processes in wastewater treatment plants
In order for wastewater to be returned to the natural environment, it must undergo a series of treatments aimed at eliminating waste and contaminants. Depending on the nature of the wastewater, treatment plants apply different processes. These phases are normally divided as follows:
- Pretreatment: In this phase, large objects that could damage the plant equipment, such as branches, plastics or stones, are removed.
- Primary treatment: It focuses on the removal of suspended solids and floating materials, such as fats and oils. It may also involve decantation or sedimentation.
- Secondary treatment: In this step, organic contaminants are removed through biological processes in which microorganisms decompose organic matter.
- Tertiary treatment: An advanced process that seeks to eliminate pathogens, phosphates, nitrates and other nutrients that may still be present in treated water.
Next, we will delve deeper into each of these treatments.
Pretreatment
Pretreatment is the first phase carried out in a treatment plant. Its main function is to prevent large and heavy objects from damaging the equipment used in later stages. During this process, screens and sieves trap materials such as branches, plastics and stones. In addition, the treatment of wastewater is carried out. desanding, which consists of removing sand and other particles heavier than water. On the other hand, the degreasing It is responsible for removing oils and greases that float on the surface using floats.
Primary treatment
Primary treatment is focused on reducing the amount of suspended solids in the water. It is carried out using decanters where the largest particles fall to the bottom by the action of gravity, a process known as sedimentation. This method is effective in removing up to 40% of suspended solids. A complementary process is that of floatation, which allows the removal of lighter materials such as oils and greases, which were not previously removed in the pretreatment. This phase may also include the use of chemicals to adjust the pH of the water, a process known as neutralization.
secondary treatment
Secondary treatment mainly uses biological processes to remove the remaining organic matter in the water. Microorganisms play a key role in this stage, as they break down the organic matter into water, biomass and gases. This process can be carried out under oxygenated conditions (aerobic processes) or without oxygen (anaerobic processes).
- Aerobic processes: By injecting air, aerobic microorganisms present in the water decompose organic matter, eliminating nitrogen compounds and other elements that could cause harmful phenomena such as eutrophication.
- Anaerobic processes: Without the presence of oxygen, anaerobic bacteria decompose organic matter generating methane, water and carbon dioxide.
A popular technique within secondary treatment is that of activated sludge, where microorganisms flocculate particles generating sludge that must be removed later. Also noteworthy are the bacterial beds and using green filters, in which special vegetation absorbs nutrients from the water.
Tertiary treatment
In certain situations, even finer treatment is required before water can be reused or discharged into water bodies. Tertiary treatment seeks to remove pathogens, nutrients such as nitrates and phosphates, and other micropollutants. Tertiary processes include the use of ultraviolet radiation, advanced filtration, ion exchange, and disinfection using chlorine or ozone. In some cases, tertiary treatment is used to treat waterborne contaminants. Inverse osmosis, a process that allows the removal of salts dissolved in water.
Sludge treatment
An unavoidable by-product of wastewater treatment is the generation of sludge, a by-product generated mainly during the settling phase. This must be managed appropriately to avoid environmental pollution. There are several processes to treat this sludge, such as anaerobic fermentation in digesters, which produces methane that can be used as biogas, or dehydration using centrifuges that allows it to be used as fertilizer.
With the continuous advancement of technology, wastewater treatment plants are playing a key role in protecting the environment and public health by purifying water and reusing waste.