Cyanobacteria, also called cyanophyta, are one of the oldest organisms on the planet. We are mostly to blame for their outbreak in still water, since they thrive on phosphates from washing powders. These detergents are now prohibited, but their reserves in the water system have not yet disappeared.
Cyanobacteria produce toxins which cause rashes or eczemas in sensitive persons. Upon contact with contaminated water, most people suffer from reddened and burning eyes. Depending on how much toxin enters the body, other symptoms may occur – from mild acute poisoning manifesting in gastrointestinal problems, through to headaches and serious liver problems. There have also been rare cases of the death of animals after drinking water contaminated with cyanobacteria.
A research team at BUT, headed by Prof. František Pochylý, CSc. has been dealing with the issue of cyanobacteria for a long time. These researchers have been trying to find a means of reducing numbers of such bacteria and preventing their further proliferation in order to improve the quality of water in general. The result of this long-term research is a method for the chemical elimination of cynobacteria which uses the principle of cavitation, in which bubbles occur and disappear based on ultrasound frequency. Not only does this solution kill cyanobacteria effectively, it enables the proliferation of microorganisms to be controlled as well.
For application of this unique method researchers selected the Brno Reservoir, in which fifteen aeration and five stirring towers were used. The towers are submerged under the water surface and constructed in a way which does not endanger swimmers or water transport. A control system situated in containers on the bank enables the performance of the aeration towers to be changed in accordance with the current situation.
Of course, we cannot influence the quality of water feeding the dam or temperatures that are favourable for cyanobacteria, in particular at the end of the swimming season.
In 2011, the aeration towers were moved closer to the surface in order to increase their effectiveness. This year has shown that the above-mentioned measures have brought about the required effect. Hygienic limits for swimming were not exceeded in any part of the reservoir (in 2010 the limits were exceeded only for a short period, and only in Rakovecká Bay and at the dam).
The following data show the maximum measured values for the number of cyanobacteria cells per 1 ml of water in 2006–2014. The hygienic limit for bathing is 100 000 cells. (Data retrieved from the source: http://www.brnenskaprehrada.cz).
| 2006 | 2007 | 2008 | 2009 |
| 35 000 000 | 38 000 000 | 42 000 000 | 5 500 000 |
| 2010 | 2011 | 2012 | 2014 |
| 120 000 | 25 000 | 29 000 | 16 000 |
Prof. Pochylý has cooperated on developing this unique technology with the Institute of Botany at the Czech Academy of Sciences, namely with Doc. Blahoslav Maršálek, CSc., alongside SIGMA Výzkumný a vývojový ústav, s.r.o., a company specializing in the development and manufacture of pumps in the Czech Republic, and the Czech company ASIO, spol. s r.o. which develops, manufactures and supplies technologies for cleaning waste water, water treatment and air purification.
The method is based on the principle of cavitation and is protected as a utility model; the principle of aeration towers as a patent.
