Buletina

The water cycle

Water is a precious natural resource. It is often said to be the source of life. But before we reach the fountain of our home, the water goes a long way. In fact, there is a huge amount of technology and infrastructure behind the faucet. The Water Consortium is responsible for the water used and drank by one million inhabitants of Bizkaia in their home, industry and shops. the water that reaches 65 municipalities has a system that has the capacity to collect 220 billion litres of water in dice mills, useful and good to drink, and whose network and pipes have a length of 400 kilometers
The average daily consumption of water per inhabitant of the Basque Country is 120 litres. The highest consumption, of course, corresponds to industries, shops and other entities.

But the reservoirs of the Basque Country have the capacity to store approximately twice the amount of water consumed per year. This water is obtained thanks to the rain that is so common here.

However, the water collected in the reservoirs is not good to drink as such. It must first be sent to the purification plant.

In this landfill treatment plant, the water in the reservoir is converted into drinking water.

ANA GARCÍA; Bilbao Bizkaia Water Consortium: The water that comes out of here is mainly drunk in Greater Bilbao. That's 3,000 liters per second coming out of here. It is distributed through pipes to the warehouses and leaves from these warehouses to all the municipalities.

Water from reservoirs typically contains impurities such as solid particles, magnesium, iron, and bacteria. All of these must be removed from the water before it is distributed for consumption. Water is also placed in the scrubber in a chlorination process to disinfect it from pathogenic substances.

Then it goes to the settling tank. It is kept motionless in it so that the impurities go to the bottom. To speed up the process, chemical reagents are added to the water. These reagents cause the particles in the water to coalesce to form heavy flakes. These flakes are deposited at the bottom of the settling tank, so that the surface water is kept clean. After the sludge that has settled on the bottom is removed and dried, it is transported to a landfill. The decanted water is passed through several filters and through several layers of sand having different thicknesses. These residual layers retain the smaller particles. Only the addition of chlorine is needed to ensure that the water has become drinkable during the distribution process.

JON ANDER ETXEBARRIA; Bilbao Bizkaia Water Consortium: Although it is believed that water has no treatment, it does have treatment. How to remove microorganisms? Well, with a dose of chlorine, which is currently in use. How to remove metals such as iron, lead and zinc? Well, with a process of coagulation or decantation that you've seen in the plant. All these processes are absolutely necessary. And yet, if the water were to get worse, even though it doesn’t have the conditions to get worse because of its geographical location, it would also be necessary to have organic removal treatments; and we have: filtration with activated carbons or other treatments.

The water quality parameters are analyzed in the laboratory of the treatment plant throughout the process: from reservoirs, rivers and fountains to the distribution network.

The control work is carried out by means of automation and remote control.

But the path of the water doesn’t end when it reaches the tap of the house. The water, after use, must be collected again for treatment and purification. In fact, the used water cannot flow as such into the river and the sea, it must first be cleaned.

In order to channel the wastewater from each locality to the treatment plants, there is a complex collection system. This siphon of the University of Deusto, for example, is a complex engineering work that is used to transport dirty water from one side of the Bilbao estuary to the other on the way to the sewage treatment plant.

Now we're going to Sestao, the wastewater treatment plant in Galindo.

Every day 350 million litres of wastewater are cleaned here. In fact, this plant has a purification capacity of 12,000 litres per second.

Water treatment begins with the removal of the larger solid waste. The water is then transferred to a tank. Here, the leftovers stop at the bottom. The grease emerges, is scraped off and the residue that has accumulated on the bottom is removed by means of a pump.

In these tanks, the organic matter contained in the water is deposited on the bottom and sludges are formed.

The water is then subjected to a biological treatment. In some barrels there is an oxygenation system that helps the bacteria to multiply. These organisms are fed with organic matter, which causes most of the dissolved matter in the water to disappear. These organisms are retained in a second decantation.

ALEJANDRO DE LA SOTA; Bilbao Bizkaia Water Consortium: We are analyzing the percentage of purification that we have in each phase. And after the biological process, which is the final process of treatment, the waters flow into the receiving environment: the estuary. We must therefore ensure that we are meeting the quality requirements for the discharge of these waters into the estuary.

As for the sludge extracted in the water decantation processes, after being treated for thickening, they are dried and transferred to a series of ovens for incineration.

ANA GARCÍA; Bilbao Bizkaia Water Consortium: it burns at 850°C, heats water, produces steam at 400°C, and is supplied to both turbines. Electricity is generated through these turbines. We sell this electricity to Iberdrola on the one hand, and we also use it directly here, in this Galindo treatment plant.

Once the wastewater has been cleaned in the treatment plants, it flows into the river. This is how the water cycle is closed. Once in the sea, the cycle will start again: evaporating the water, turning it into fog and rain, filling the reservoirs, taking it to the treatment plants, distributing it for consumption, collecting the discharges, cleaning the wastewater, pouring it into the river...

Elhuyar Zientzia