The fundamental information of any product that is consumed, be it food or drink, appears on the label. The most relevant information on its identification, description and components must appear on the label. Bottled water also has its corresponding label, which in addition to fulfilling its role in terms of purchasing decision, must respond to the need to know the type of product that is offered inside each bottle.
When we talk about the management of drinking water, it is inevitable to wonder how water, from its different sources, reaches our homes converted into drinking water. As we mentioned in previous articles , supply systems collect water from different sources: rivers, streams, reservoirs, wells, springs, reservoirs, among others. Once that raw, untreated water is stored, that is when the ETAP .
Convert stored water into drinking water
When we talk about ETAP we refer to the Drinking Water Treatment Station, also known as the Potabilizadora. It is an industrial facility in which the appropriate treatments are carried out to precisely make all that water collected and stored from different sources become completely safe and suitable for human consumption.
How does an ETAP work?
Although its appearance at first glance is that of a perfect water to drink, the water that reaches the water treatment plants contains numerous pollutants that are harmful to health. These biological, chemical and even radioactive pollutants must be completely eliminated through the appropriate treatments.
Although there are various types of water treatment plants, normally, to achieve this end, they carry out a series of continuous processes whose generalized sequence is as follows:
- Pretreatment or pre-sedimentation: The water reaches a large deposits in which settleable solids are removed. The heavier particles fall to the bottom when the water movement stops.
- Flocculation: the coagulation or flocculation process consists of adding chemical additives to the water to promote the sedimentation of non-sedimentable colloidal matter or to accelerate the sedimentation through the formation of flocs. Flocs are groups of small particles agglutinated into larger particles with a greater sedimentation capacity.
- Sedimentation: Due to the effect of gravity, the flocs settle to the bottom of the tanks to be eliminated.
- Filtration: The water passes through a porous medium that is responsible for retaining the remaining impurities. Once this phase is finished, the water will be completely clean, although it will not yet be suitable for consumption.
- Disinfection: In this phase the bacterial load of the water is reduced. This treatment is carried out with different methods, either ozone or ultraviolet rays for its subsequent chlorination that will achieve clean water and, now, totally drinkable.
The arrival of water at home
After disinfection, before reaching homes, the water must pass strict controls that verify the real quality of the product obtained in the water treatment plant. Thus, in Spain, it is the National Information System for Drinking Water, the body in charge of this control and the collection of data on the characteristics and qualities of the water from the ETAP.
Once this quality is verified, the water is stored in tanks near the water treatment plants until it is transported to homes, receiving a contribution of chlorine that favors its conservation in those tanks.
Chlorination is one of the processes that are carried out to treat water and its objective is to carry out a disinfection of all kinds of bacteria and pathogenic organisms. The ultimate goal of these treatments is to obtain drinking water that can be consumed by humans without risk to their health. But, is there any risk in the fact that this chemical has a presence in the water we drink? We will analyze it below.
One of the bases of correct water management lies in its adequate reuse once it reaches the final phase of the cycle. At this point, it requires a process and treatment before being returned to the natural environment in optimal conditions, which is carried out precisely in the WWTP: Industrial water treatment. Dumping wastewater into rivers without carrying out the corresponding treatment implies generating an environmental impact with fatal consequences. Next we will see what this process consists of.
Clean water and sanitation
Institutions such as the UN point to clean water and sanitation as one of the Sustainable Development Goals of their Development program. To meet this objective, the treatment plants carry out this work of cleaning and treating wastewater to be able to return it to nature free of waste harmful to the environment.
What is wastewater?
They are the waters coming from homes, businesses, industry and agriculture, once they have been used for the purposes that each place requires. Thus, the water discarded from the washing machine at home, or that used to cool the turbines of a factory, is directed through the sewage network to some collectors that finally end up in the purification station. Domestic wastewater contains organic and suspended pollutants while industrial wastewater can also add heavy metals and hydrocarbons. In this way, these waters with toxic substances of inorganic nature are forced to undergo a previous treatment in the facilities where they are generated before going to the municipal collectors.
Once the domestic and industrial wastewater passes to the collector, the water purification phases will begin, which aim to eliminate organic residues such as oils, fats, sand and sedimentable solids as well as chemicals such as ammonia and phosphorus. In addition, in the last steps, the retained waste will be transformed into stable sludge that will also be reused.
How does a WWTP work?
In the treatment plant, the water will go through four well-defined phases:
- Pretreatment: After entering the station, larger waste is removed through screening grids that retain garbage and other bulky items; later on, it goes to tanks in which suspended sand and grease are removed thanks to mechanical processes. From here it will go to the primary decanter to continue with the process.
- Primary Purification: In this decanter, the water will remain at rest to favor the deposit of the heaviest residues at the bottom. These residues will generate a sludge that will be separated from the water and stored in a sludge digester prepared for this purpose.
- Secondary Treatment: The water passes into tanks to which oxygen bubbles are added to promote the proliferation of microorganisms that will be responsible for removing the dirt that remains. This biochemical process will eliminate organic matter such as ammonium which, if it remains, will consume the dissolved oxygen available for aquatic fauna and flora once the water is returned to the natural environment. In this phase, new sludge is created that will separate from the water and go to the sludge digester.
- Tertiary Treatment: In this phase a settling, filtration and disinfection of the water is carried out. After this process, the water is returned to the natural environment in the best conditions so that it can continue its cycle.
What happens to the waste after the process?
The wastewater treatment process, as we have detailed, generates sludge that is collected through the different phases of this process. This matter and its biological reactions are reused for different purposes. On the one hand, when stabilized and extracted, this sludge produces biogases that are used as energy, and even as biofuel for vehicles. On the other hand, the sludge itself generated is used as organic fertilizer, replacing in many cases chemical fertilizers that are harmful to the environment. Finally, the algae and other microorganisms that proliferate in the process are also used to generate biomass, among other uses.
This interesting video helps us to understand in detail this process of collecting and treating wastewater as well as the subsequent management of this waste.
Thus, with the treatment of the water that we discard every day, we not only contribute to returning to nature that resource so necessary for our daily life, but it also arrives in perfect condition so that it can contribute to the environmental balance that we need.
The treated water returns to the natural environment, but is also used in:
- Urban uses: street cleaning, irrigation, sanitary uses, etc.
- Industrial uses: for example for the cooling of machines.
- Agricultural and livestock use: cleaning, irrigation of crops, etc.
- Other functions such as golf course irrigation, aquifer recharge, etc.
The largest treatment plants in the world
Atotonilco WWTP (Mexico)
It is the largest Wastewater Treatment Plant in the world, which treats all the waters of the Valley of Mexico destined to irrigate 80,000 hectares of land.
Stickney WWTP (Cicero, Illinois, United States)
Its 230 hectares of surface supply the entire city of Chicago and other areas and its water pumping station, lifts them from a system of tunnels to almost 100 meters deep
Bailonggang WWTP (Shanghai, China)
The main wastewater plant on the Asian continent with 24 hectares of surface, is responsible for the purification of a third of the waste that is dumped daily into the waters of the Yangtze River.
The importance of wastewater treatment
In summary, the Wastewater Treatment Stations contribute to reducing the waste generated. The recycling of wastewater minimizes waste, to which it is convenient to contribute with responsible use so that our future generations can continue to have the water resources necessary for life.
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