Chlorine dioxide is considered much more powerful than chlorine or sodium hypochlorite, which are used in potable water disinfection or as antifouling agents in seawater.
The enhanced biocidal action is more evident in case of seawater treatment in fact, chlorine dioxide performance does not depend on the seawater pH as in the case of chlorine or hypochlorite.
ISIA's chlorine dioxide generator works “under water”. It means that the formation of chlorine dioxide takes place only inside the water to treat itself, and it is not present in any part of the plant. Therefore, we always have a very diluted solution and never ClO2 gas. In normal generators you can find in the market, instead, chlorine dioxide is generated into a reaction chamber having a big volume: for instance, to generate 10 kg/h the volume is 70 litres, in our generator the volume to generate the same quantity is 0.5 litre only. As you can understand, the danger of releasing chlorine dioxide in the ambient depends on the quantity of material you have at the site in any moment.
The chlorine dioxide reaction chamber is the only place where chlorine dioxide is generated. Sodium chlorite and hydrochloric acid, arriving from the reagents pumping station, through two special flexible small pipes, meet each other inside the reaction chamber, which is very small, completely submerged by the dilution water and under the water to be disinfected. In this manner, chlorine dioxide will never be released in the surrounding area giving 100% safe operation. Chlorine dioxide is immediately dissolved in the dilution water (solution of 1 g/l) and distributed inside the basin through a proper spreader.
In case chlorine dioxide has to be injected in a water line and not in a basin, thus the reaction chamber is placed inside a 2-3 inch dilution water line and ClO2 solution injected into the lines of water to be disinfected.
Advantages on seawater
The seawater pH is around 8.5, at that pH value chlorine is almost converted into hypochlorite ion, which is negative charged and only around 20% remains as un-dissociated hypochlorose acid.
Since also the bacteria wall is negative charged, hypochlorite cannot enter the cells to kill them, only hypochlorose acid can be active at that pH. That means you add 1 mg/L of chlorine but actually only 0.2 mg/L is effective against the seawater life.
On the contrary, chlorine dioxide acts as a gas dissolved in the seawater. It does not give dissociation and it is able to penetrate the bacteria cells in the same manner of the oxygen dissolved in the water. In other words, bacteria breaths chlorine dioxide instead of oxygen and die. Thanks to this characteristic, chlorine dioxide dosage rate is normally 3-5 times less than chlorine or hypochlorite providing even better performance.
We have a lot of examples in Power stations and petrochemical plants where seawater is used for their once through cooling systems.
Advantages on Potable water
In potable water disinfection, again, chlorine dioxide is much more efficient than chlorine or hypochlorite and avoids formation of bromates and THMS. Just to give you an example, in Qatar, up to 2007 they used hypochlorite for disinfection and the water analisys revelead that there was more than 10ppms of bromates; since year 2013, when they completed the transition to ClO2 disinfection, bromates are no more detected (Drinking Water Quality Management in the state of Qatar, the 2nd Arab water conference, 2014, Qatar)
Chlorine dioxide (ClO2) selective reactivity makes it a powerful oxidizing agent useful in many water treating applications for which chlorine and other oxidizing agents are unsuitable. Unlike chlorine, chlorine dioxide does not react with naturally occurring organic materials to form trihalomethanes (THMs). Chlorine dioxide aids in reducing the formation of TTHMs and haloacetic acids (HAA) by oxidizing precursors, and by allowing the point of chlorination to be moved farther downstream in the plant after coagulation, sedimentation, and filtration have reduced the quality of natural organic material (NOM).
THMs are produced when free chlorine or bromine reacts with natural organic matter in the water. The identification of THMs in chlorinated water supplies led to concerns over their potential health effects including reproductive effects and the classification of chloroform, bromodichloromethane and certain other disinfection by-products (DBPs) as carcinogens.
Chlorine dioxide prevents THM formation by disinfecting without chlorinating organic materials and by oxidizing the organic THM precursors. This means that pre-treatment with chlorine dioxide has an inhibiting effect on THM formation when chlorine is subsequently used for treatment. Pre-treatment with chlorine dioxide oxidizes the THM precursors, which are removed during coagulation, settling, and filtration before final chlorination. This modification of standard chlorination practices can result in a 50-70% decrease in TTHMs in the finished water.