Hostivař reservoir – Prague

Application of ultrasound at Hostivař reservoir

  • Client: Prague City Hall
  • Location: Prague – Hostivař
  • Duration: 2018
  • Total cost: 474,000 CZK

Hostivař reservoir is the largest area of water in Prague, serving primarily for flood protection and recreational purposes. Only a few minutes’ drive from the centre of Prague, it is a natural swimming pool, and one of the most beautiful natural sites in the capital.

Hostivař reservoir in Prague has long been suffering from the growth of cyanobacteria, which in the summer months significantly reduces the quality of the water in the reservoir. In the summer of 2017, the water in the reservoir was evaluated by the Institute of Health Information and Statistics of the Czech Republic as being “Water Dangerous for Bathing”.

Prague City Hall decided to solve this unpleasant situation by treating the water using our ultrasonic technology for the elimination of cyanobacteria. In mid-May 2018, we placed three autonomous floating units on the reservoir, which were fitted with solar panels with batteries. The solar energy powers an ultrasonic transmitter both during the day and thanks to the batteries even at night. The ultrasound wavelength of each unit is 400 m in each direction. Therefore, each unit treats a radius of 800 m.

In order to assess the effect of ultrasound on Hostivař reservoir, data from 2017 before the ultrasound application and from 2018 when the ultrasound was applied were compared. Compared to 2017, 2018 was characterized by lower total rainfall, a significantly higher degree of sunshine, and with it, higher average temperatures (e.g. April 2018 exhibited the same temperatures as May 2017). From a meteorological point of view, therefore, 2018 was significantly more favourable for the development of cyanobacteria than 2017.

Throughout the 2018 season, it was possible to maintain nearly half of the Chlorophyll-A values and double the transparency of the water compared to 2017. It was also possible to maintain the cyanobacterial concentrations well below the values recorded at the end of the 2017 season. The extremely favourable climatic conditions and overall warm weather led to an increase in the concentrations of cyanobacteria at the end of the summer. Sampling and analysis of water were performed by the independent laboratory PEAL s.r.o.