Ozone solutions for water sterilization


Water sterilization is recommended whenever drinking water is to be consumed, when retrieving water from a contaminated well or other sources, or any time surface water is treated prior to consumption. Ozone is the most effective water sterilizing method available today. The ozone is highly effective in destroying pathogens, and when its work is completed, it breaks down into oxygen (O2). This form of oxygen does not adversely affect the taste of the water.

On the contrary, the added dissolved oxygen enhances the water's taste. Advantages include highly effective sterilization, no unpleasant tastes or odors, and no significant residual effect. Ozone does sterilize the bottle, and its residual effect continues sterilizing for a time. Lastly, the human body's dependence on water and the potentially serious consequences of consuming contaminated water should value the significance of this method of water sterilization.

Taste and odour control

Most tastes and odors in water supplies come from naturally-occurring or man-made organic material contamination. Bacterial decomposition of humid material imparts taste to surface waters. The action of algae and actinomycetes gives rise to objectionable tastes. Chlorination of humic material leads to chlorophenols that are of far stronger odor and more antagonistic to taste than the original phenol and unreacted Chlorine. Most of these odors are removed with Ozone treatment. Even some sulfur compounds such as hydrogen sulfide, mercaptans or organic sulfides can be oxidized to Sulfates with Ozone.

Removal of heavy metals

Ozone oxidizes the transition metals to their higher oxidation state in which they usually form less soluble oxides that are then easy to separate by filtration. Iron, for example, is usually in the ferrous state when dissolved in water. With Ozone it yields ferric iron which is further oxidized in water to Ferric Hydroxide — a molecule that is very insoluble and precipitates out. Other metals such as Arsenic (in the presence of Iron), Cadmium, Chromium, Cobalt, Copper, Lead, Manganese, Nickel, and Zinc can be treated in a similar way. At Ozone levels above 4 ppm however, Manganese will form soluble permanganate, showing up as a pink color.

Color removal

Surface waters are generally colored by natural organic materials such as humic, fulvic and tannic acids. These compounds result from the decay of vegetative materials and are generally related to condensation products of phenol-like compounds; they have conjugated carbon/carbon double bonds. When the series of double bonds extend upwards of twenty, the color absorption shows up in the visible spectrum. Ozone is attracted to breaking organic double bonds. As more of these double bonds are eliminated, the color disappears. Surface water can usually be decolorized when treated with 2 to 4 ppm of Ozone.

Algae removal

Ozonation of water contaminated with Algae oxidizes and floats the Algae to the top of the reservoir. The ozone will also oxidize the metabolic by-products of the Algae and remove the undesirable odor and taste.

Improve coagulation and turbidity removal

Oxidation of dissolved Organic materials with Ozone results in polar and charged molecules that can react with Polyvalent Aluminum or Calcium to form precipitates. Treatment of surface water with up to 0.5 ppm of Ozone results in a decrease in turbidity, improved settle ability, and a reduction in the number of particles. This treatment, referred to as pre-ozonation, destabilizes the colloid with a resulting reduction in the amount of coagulant needed to produce a clear filtrate.

Ozone reactions to organics

Ozone reacts rapidly with most simple aromatic compounds and unsaturated aliphatics, such as Vinyl Chloride, 1,1-dichloroethylene, trichloroethylene, and p-dichlorobenzene. Benzene, etc. But it reacts slowly with complex aromatics and saturated aliphatics. Ozone will degrade many organic compounds, such as sugars, phenols, alcohols, and as it degrades these materials it turns again into Oxygen. Coupling Ozone with Hydrogen Peroxide will cause the formation of very active Hydroxyl ions which initiate a nucleophilic attack on organic compounds. This can result in the displacement of Halogens and other functional groups such as Amines, Sulfides.

If oxidable chemicals are present in the water, larger amounts of Ozone will dissolve to satisfy the demand. One limiting factor is the efficiency of the mass transfer device used. When using Venturi, more turbulence and smaller bubbles facilitate better mass transfer. When using Bubble Diffusers, the water column should be at least 16 ft. high. Higher concentrations of Ozone in water cause more vigorous oxidation of even more resistant organic compounds.

Additional Information

Ozone vs Chlorine

When comparing disinfection efficiency, Ozone is 25 x more effective than Hypochlorous acid (HOCl), 2,500 x better than Hypochlorite (OCl) and 5,000 x more than Chloramine (NH2Cl). These results are measured from the comparison of CT constants — the Concentration x Time needed to kill 99.99% of all micro-organisms. Chlorine reacts with organic materials to form organics containing Chlorine such as Chloroform, Carbon Tetrachloride, Chloromethane and others, generally known as Trihalomethanes (THMs).

Ozone reacts with Organics to break them down into simpler compounds. These organics (Oxalic Acid for example) do not readily break down all the way to Carbon Dioxide with just Ozone, but if subjected to bacterial degradation on activated charcoal, they will be removed. This water can be later treated with a low level of Chlorine, say 0.2-0.3 ppm, to maintain sanitation in the distribution system.

This way no THMs will be formed. THMs have been implicated as carcinogens in the development of Kidney, Bladder and Colon Cancer. The regulatory authorities are again decreasing the allowable levels of THMs in Community water systems. At the present time the limit is 0.05 ppm. Based on the scientific research, the level will be most likely soon be lowered to 0.01 ppm. Ozone does not react significantly with THMs as they are more resistant to oxidation - it takes a very long time to achieve full oxidation. Some THMs are removed as a result of physical sparging by the aeration action of the ozone/air mixture.

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