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What is wastewater? 

Wastewater is water that has been negatively affected by human action, and it requires treatment to be purified and reusable. Waters that aren’t suitable for use due to natural causes are not included in this classification, nor are those that have already been used by people but are still usable.

Where does wastewater come from? 

Wastewater is water that has been used in domestic and urban environments or in industries and livestock. It also includes natural water that, whether by accident or malpractice, has been mixed with the previous ones. 

Depending on where it comes from, wastewater may contain various pollutants, either solid or dissolved.

How is wastewater classified? 

Wastewater can be classified according to its quantity and the type of chemicals it contains; according to its bacteriological characteristics; according to the ratio of water and suspended matter and dissolved matter; or depending on its origin.

The last of these, its origin, is the most common form of classification. We can break that type of wastewater down further into four subcategories (which, in turn, may be subdivided into other categories).

Urban or domestic wastewater: it results from the use of water in homes and urban centers, where many businesses and workplaces are also concentrated. This type of wastewater is especially high in organic pollutants and sedimentable solids, as well as bacteria.

Industrial wastewater: this results from the processes of the economy’s secondary sector – that is, industrial activities. This includes the water discarded by factories, energy production plants, or any other activity destined to manufacturing consumer products or manufactured products.

Industrial wastewater is characterized by a high level of synthesized chemicals and heavy metals (including lead, nickel, copper, mercury, and cadmium, to name a few).

Wastewater from agriculture and livestock: these come from the primary sector of the economy. For the most part, they are produced by livestock, especially intensive livestock farming. Agriculture produces almost no wastewater because it uses most of it for irrigation. However, some crops and activities destined for treating certain agricultural products use abundant water that later becomes waste.

These waters contain high levels of pollutants that come from certain chemicals used for raising livestock, as well as feces and urine from animals.

Wastewater from rain: this type of wastewater is produced when rain carries pollutants present in the atmosphere, especially urban centers, to the ground, polluting it. Most of this water ends up in the public sewer, where it flows into domestic or urban wastewater. 

How is wastewater treated? 

Wastewater treatment, or wastewater purification, consists of a series of physical, chemical, and biological processes that aim to eliminate the pollutants present in water resulting from human use or other uses. Treatment begins by collecting water from urban centers and industrial sectors, and the goal is to return it to the water cycle, either by pouring it into the sea or reusing it.

The main treatment methods include the primary settler (gravitational sedimentation), dissolved air flotation (separation of suspended particles by using bubbles), and chemical treatments. However, all purification processes usually have three main phases: primary treatment (decantation), secondary treatment (biological process of eliminating organic matter and secondary decantation), and treatment of the sludge produced in the previous stages. 

What wastewater treatment benchmarks are there in Spain?

Spain’s water sector has undergone a marked transformation in recent decades. Despite the fact that significant progress has been made, such as improving wastewater sanitation and developing water reusage, progress so far has been insufficient to face the major challenges in the sector.

The Ferrovial Company is an expert in the design, construction, operation, and maintenance of potable water, urban wastewater, industrial water, and desalination. The activity is carried out sustainably and with respect for the environment through two companies: the multinational Cadagua and the U.S.’s PLW Waterworks. They have more than 460 references in the design and construction of water treatment plants that reach an aggregate capacity of almost 18,000,000 m³ each day and historically serve more than 41,000,0000 inhabitants.

Fun facts about wastewater

  • Every year, 1.8 billion people risk contracting diseases like diarrhea, cholera, dysentery, and polio from drinking water contaminated by feces.
  • Every day, about a thousand children die from preventable diarrheal diseases related to water and sanitation.
  • More than 80% of wastewater is discharged into rivers or the sea without the pollutants being removed.
  • In Spain, 5,000 cubic hectometers of water are purified each year.

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