Ozone Treatment For Cooling And Potable WaterPresented by:

Introduction

Cl2 gas is used to control biological growth in cooling tower water.Cl2 gas / bleaching powder is used to disinfect drinking water.Ozone treatment of above water is gaining popularity as it is far more effective in controlling biological growth & disinfection.Its handling involves minimum hazards.

About the technologyOzone(O3)is a molecule consisting of three oxygen atoms.It is a powerful biocide and virus de activant.It oxidizes many organic & inorganic substances.

GenerationOzone is generated by passing a high voltage AC(6 -20 kV) across a dielectric discharge gap through which oxygen is injected.2 Oo2O + O2 o3Electric arcO2 O2

O2O3WATERWATEROZONISERALUMINIUM ELECTRODE6 - 20 KV AC

Concerns of drinking waterBy-product of Cl2 treated water are chloramine, dichloroamine , which are proven carcinogens.Disagreeable smell and taste.Ozone is safe disinfectant , no health hazard as only by-product is oxygen.

Maintenance concerns of cooling towersBiological growthScalingCorrosion

Biological growthContinuous exposure to airbourne organic matterBuildup of bacteria, algae, fungi and virusesHazardous for the tower system & health of humans encountering the water.Legionnaires disease caused by a legionella bacteria thriving in cooling water environment

Biological growthIncreases risk of microbially induced corrosion.Certain sulphate reducing and iron metabolising bacteria can destroy iron pipes.Biofilm coating on heat exchange surfaces reduces heat transfer efficiency.

Control of biological growthOzone kills bacteria by rupturing the cell walls, process to which micro organism cannot develop immunity.Residual ozone concentration 0.4 mg/l results in 100% kill in 23 min for biofilm producing bacteria.Residual ozone conc. 0.1mg/l removes 70-80 % biofilm in 3 hrs.

O3Other disinfectants

ScalingAs the water in cooling tower evaporates, dissolved solids concentrate in a circulating water.Biofilm acts as an adherent for these mineral micro crystals.Over time deposition of organic & inorganic matters increases scale thickness.Ozone loosens and removes the scale by removing the biofilm.

CorrosionMuch of the corrosion in cooling towers are microbiologically induced.Ozone prevents corrosion by controlling microbial populationOzone treated cooling water rises pH to above 8.5 providing corrosion protection.

Benefits Energy saving 1. Less makeup water. 2. Blowdown can be reduced.Water saving Less water consumption.

Other benefitsReduces chemical useEliminate infectious bacteriaImprove regulatory environmental compliances.Finally from HR perspective, reduced risk of personnel health enhances the working environment and makes a positive public statement.

LimitationsSolubility Half lifeHigh COD High temperature

Comparison

Operating cost comparison for cooling water system per yearRs. 0.0Rs.6,00,000Power consumption Rs. 5,000 > 50,000Rs. 1,50,000Rs.4,50,000LabournilRs.10,00,000ChemicalsRs 11,50,000nilElectrical operationOzone treatmentChemical treatmentItemSafety Equipments

Conclusion Through laboratory testing, field testing and theoretical analysis, ozone treatment of cooling water has shown to be technically valid and economically attractive in many applications.The technology works by virtue of the ability of ozone to act as a disinfectant and therefore as an alternative to traditional chemical treatment.