Ozone is a powerful oxidising agent which, when dissolved in water, produces a broad-spectrum biocide that destroys all bacteria, including biofilm and legionella.
Since 1906, ozone has been used in the disinfection of potable water supplies. Uses and applications for ozone have continued to develop, notably in the more demanding high-risk applications such as bottled drinking water, pharmaceutical process water, effluent treatment and swimming pool treatment.
Applications in cooling water treatment have continued to develop throughout the world with well-documented evidence of its effectiveness. Initial concerns over the corrosive effect of ozone in cooling water applications have proven unfounded with results from applications showing reduced corrosion when compared with other oxidising biocides.
Tests have shown clearly that ozone destroys all bacteria including pseudomonas (responsible for biofilm) and Legionella, at concentrations of 0.4 to 0.5 mg/ltr. Ozone produced a 100% kill of pseudomonas in bulk liquid in 2 to 3 minutes. Removal of biofilm could be achieved by using ozone at concentrations of 0.08 to 0.33 mg/ltr for two to six hours (KAUR et al – University of Birmingham).
In studies of the effects of various biocides on Legionella p. serogroup1, a greater than 99% kill was achieved using a concentration of 0.1 to 0.3 mg/ltr ozone, maintained for five minutes (RL Tyndall et al).
The Filtex ozone system provides a fully automatic water quality management and treatment system utilising the following key elements:-
- The use of ozone produced electrically from air as an oxidising biocide in the water to control all bacteria biofilms, including legionella.
- The removal of dirt and suspended matter by cyclone filtration.
- Control of dissolved mineral salts using conductivity controlled bleed-off.
The Filtex ozone unit comprises 2 modules fixed together as a single integrated package:
One for sidestream filtration and ozone injection units and one for ozone generator and control equipment.
Water is drawn continuously from each cooling tower sump and pumped through a cyclone filter to remove suspended solids. After passing through the filter the water passes through a venturi eductor, which draws ozone from the ozone generator and mixes it with water.
The filtered water with dissolved ozone is returned to the cooling tower pond via the manifold and series of eductor mixer nozzles. The eductor nozzles ensure effective mixing of the ozonated water with the water in the tower pond and provide an agitation to purge to the pond of settled debris and drive it towards the filter suction.
The ozone, mixed with the cooling water, is circulated through the cooling water system by the spray water pump, providing continuous disinfection and biological control throughout the evaporative cooling circuit in a similar manner to other oxidising biocides such as bromine and chlorine.
The sidestream cyclone filters are automatically purged of collected solids by motorised ball valves, which also provide bleed-off to control dissolved solids. The auto purging and bleed-off is controlled by a timer in the main control plc and the conductivity controller to minimise wastage and water loss.
In normal operation, the conductivity controller will provide adequate operation of the purge valve to also purge the filters. Only if the system is on light load with minimal evaporation, and therefore negligible bleed-off requirement, will the timer override be activated to carry out filter purging.