Karlovy Vary - where does drinking water flow to households and where does it end?

The last stop in our journey will be in the Karlovy Vary Region. With 86.7 litres/capita/day, it ranked among the regions with slightly below average daily household water consumption in 2018. At the same time, it is the only region in the Czech Republic where 100% of the population is supplied with water from water supply systems and at the same time all households are connected to a sewage network with a wastewater treatment plant. ^(1,2)

Due to the lack of underground water sources in western Bohemia, an extensive network of group water supply systems was built in the area from the second half of the 20th century. These drew on good quality surface sources with drinking water treatment plants and replaced unreliable local sources. One of these is the Karlovy Vary Regional Waterworks, which supplies water to more than 116 000 people in Karlovy Vary, Chodov, Ostrov and other towns ^.

The main surface source of drinking water in this case is the Stanovice Dam on the Lomnický Brook. It falls within the water protection zone and therefore there is no risk of industrial, agricultural or urban pollution. The reservoir can hold up to 24.2 million^{m3 of} water, of which about 22 000^m3 is diverted every day to the Březová water treatment plant. Before the actual treatment, the raw water is passed through a small hydroelectric power plant and a heat pump, making the waterworks largely energy self-sufficient.

The Březová WWTP was commissioned in 1984 as a two-stage plant, but during the reconstruction between 2011 and 2016 it was expanded to include a third stage, the so-called ultrafiltration - one of the most modern technologies for the production of drinking water^.(4)This uses membrane ultrafiltration fibres with capillaries, which are 4 mm thin plastic tubes with 20 nm diameter pores in the walls. As water passes through these fibres, remaining insoluble substances, including pathogens up to the size of viruses, are captured. In contrast, elements important for humans, such as magnesium or calcium, pass through. ⁽⁵⁾ This method of water treatment makes it easier to maintain high water quality even during seasonal fluctuations, makes it possible to use surface water from the Ohře or Teplá rivers if necessary, and allows chlorine doses to drinking water to be reduced. When using this technology, it is essential to ensure frequent flushing (approximately every hour), continuous disinfection and checks on the integrity of the fibres ^.

ÚV Březová - settling tank
source: vodakva.cz

After the raw water has been treated into drinking water, its hardness is additionally increased - it is enriched with minerals beneficial to humans (Mg, Ca), because the water in Stanica is only slightly mineralised. At the same time, a corrosion inhibitor is added to the water, which protects the surface of the pipes from the inside and prevents the release of iron into the water ^.

However, water is also supplied to the Karlovy Vary regional water supply system from underground sources of the Hřebčná spring and boreholes near Boží Dar and from the ÚV Myslivna, which was established in 1952 for the needs of the Jáchymov mines. The latter draws water from the Myslivna dam of the same name, which is the highest water reservoir in the Republic. The quality of this water is very low and variable, mainly due to the adjacent peat bogs.

The Drahovice Wastewater Treatment Plant in Karlovy Vary currently treats wastewater from more than 60,000 inhabitants of the regional town and surrounding municipalities as well as from industrial wastewater producers. In addition to the treated water that is discharged into the Ohře River, a significant amount of waste product - sludge - is produced (as in other WWTPs).⁽⁸⁾ The biogas produced from its digestion has been used for the production of heat and electricity since 2007. Sludge is also often taken to composts and landfill reclamation, but the sludge from Karlovy Vary cannot be used due to its higher arsenic content in agriculture and is therefore only sent to landfills ^.

The sludge contains, in addition to organic matter, which is subject to putrefactive decomposition, pathogenic micro-organisms and quite a lot of water, which complicates its transport. It is therefore necessary to remove the excess water and dangerous substances beforehand. In 2016, a low-temperature sludge drying plant - the first of its kind in the Czech Republic - began operation in Drahovice. At 80 °C, sludge can be concentrated to a dry matter content of up to 90% and reduced to a quarter of its weight (using centrifuges, it is only about 25% dry matter). At the same time, at this temperature there is no risk of explosion or ignition of sludge. In addition to reducing the volume of sludge, which facilitates transport and its possible subsequent energy recovery, this treatment also achieves better hygiene (⁹⁾.

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