Applications of ClO2 : to Enhance Disinfection Efficiency

Chlorine dioxide (ClO2) is a highly effective, environmentally  friendly microbiocide. It is a selective oxidant that attacks both  planktonic and sessile bacteria,

disinfects surfaces, and rapidly  reduces biofilms. ClO2 is a stable, dissolved gas that is a strong bactericide  and virucide at concentrations as low as 0.1 ppm. ClO2 is an effective  disinfectant that penetrates the cell walls microorganisms and disrupts  metabolic functions. This is more efficient than other oxidizers that “burn”  whatever they come in contact with. With minimal contact time, it is  highly effective against Legionella, Amoebal cysts, Giardia cysts, Listeria, Coliforms including E-Coli, Staphylococcus, Salmonella, and
Cryptosporidium. ClO2 is also effective against virus, mold, yeast, algae and fungus. It provides a practical solution for the problems associated with phenols, sulfides, iron and manganese contaminants, and their taste and odor within water systems. ClO2 reduces biofilms so bacterial re
growth is significantly impeded.
Chlorine dioxide’s effectiveness is not limited to just odor-related problems. When used in water disinfection, it does not form chlorinated or brominated by-products, such as trihalomethanes (THMs) or haloacetic acids (HAAs), both of which cause concern for health and will soon come under strict regulatory limits.
Another advantage of Clo2 is that it does not ionize to form weak acids (as chlorine and bromine do) in aqueous solutions. This allows ClO2 to be effective over a wide pH range.
Biocidal Efficacy of ClO2:
It is the only biocide that is a molecular free radical. It has 19 electrons and has a preference for substances that give off or take up an electron. Chlorine dioxide only reacts with substances that give off an electron.

Chlorine, oppositely, adds a chlorine atom to or substitutes a chlorine atom from the substance it reacts with. No biocide has proven to control biofilm better than ClO2. It reduces or eliminates the biofilm where bacteria thrive and reproduce, causing these organisms to be significantly reduced within a water system. Other oxidizers react mostly on the surface of the biofilm to form an oxidized layer, like charring on wood. This precludes further penetration. ClO2 is a dissolved gas that penetrates biofilm by molecular diffusion. It travels to the base of the film where it attacks microorganisms and loosens the biofilm at its point of attachment. Substances of organic nature in bacterial cells react with chlorine dioxide, causing several cellular processes to be interrupted. Chlorine dioxide reacts directly with amino acids and the RNA in the cell. Chlorine dioxide can penetrate the slime layers of bacteria, because chlorine dioxide easily dissolves, even in hydrocarbons and emulsions. Chlorine dioxide oxidizes the polysaccharide matrix that keeps the bio film together. During this reaction chlorine dioxide is reduced to chlorite ions.

Mode of action:

Chlorine dioxide (ClO2) acts as an oxidizing agent and reacts with several cellular constituents, including the cell membrane of microbes. By “stealing” electrons from them (oxidation), it breaks their molecular bonds, resulting in the death of the organism by the break up of the cell. Since chlorine dioxide alters the p r o t e i n s i n v o l v e d i n t h e s t r u c t u r e o f microorganisms, the enzymatic function is broken, causing very rapid bacterial kills. The potency of chlorine dioxide is attributable to the simultaneous, oxidative attack on many proteins thereby preventing the cells from mutating to a resistant form. Additionally, because of the lower reactivity of chlorine dioxide, its antimicrobial action is retained longer in the presence of organic matter.

Environmental impact:

Chlorine dioxide’s special properties make it an ideal choice to meet the challenges of today’s environmentally concerned world. Actually, chlorine dioxide is an environmentally preferred alternative to elemental chlorine. When chlorine reacts with organic matter, undesirable pollutants such as dioxins and bio-accumulative toxic substances are produced. Thus, the EPA supports the substitution of chlorine dioxide for chlorine because it greatly reduces the production of these pollutants. It is a perfect replacement for chlorine, providing all of chlorine’s benefits without any of its weaknesses and detriments. Most importantly, chlorine dioxide does not chlorinate organic material, resulting in significant decreases in trihalomethanes (THMs), haloacetic acids (HAAs) and other chlorinated organic compounds and it is more effective at lower dosing levels.

Thus, Chlorine dioxide is approved and recommended

by the U. S. Environmental Protection Agency as an environmentally friendly drinking water additive to replace chlorine. The U. S. Food and Drug Administration permits the use of

c h l o r i n e d i o x i d e i n m a n y f o o d applications. ClO2 is in widespread use in The United Kingdom and continental Europe. In the UK, the Building Services Research and Information Association (BSRIA) has recommended ClO2 as the best available technology for control of Legionella in hot and cold water systems.

The criteria for disinfection, as defined by the USEPA, are as follows. ClO2 meets all of these criteria.

1.A 99.9% reduction in Giardia lamblia (3 log reduction).

2.zero lactose fermenting coliform

3.less than 10 cfu/mLnon-lactose fermenting colifor 99.99% reduction in enteric virus (4 log) concentrations.

What are the disinfection byproducts of chlorine dioxide?

The reaction process of chlorine dioxide with bacteria and other substances takes place in two steps. During this process disinfection byproducts are formed that remain in the water. In the first stage the chlorine dioxide molecule accepts an electron and chlorite is formed (ClO3). In the second stage chlorine dioxide accepts 4 electrons and forms chloride (Cl-). In the water some chlorate (ClO3), which is formed by the production of chlorine dioxide, can also be found. Both chlorate and chlorite are oxidizing agents. Chlorine dioxide, chlorate and chlorite dissociate into sodium chloride (NaCl).

HowdoesCl02generated?

Traditionally, chlorine dioxide for disinfection applications has been made by one of three methods

1)Using sodium chlorite or the sodium chlorite –

hypochloritemethod:

2NaClO2+2HCl+NaOCl→2ClO2+3NaCl+H2O

2)or using the sodium chlorite – hydrochloric acid

method:

5NaClO2+4HCl→5NaCl+4ClO2+2H2O

All three sodium chlorite chemistries can produce chlorine dioxide with high chlorite conversion yield, but unlike the other processes the chlorite- HCl method produces completely chlorine free chlorine dioxide but suffers from the requirement of 25% more chlorite to produce an equivalent amountofchlorinedioxide.

3) Very pure chlorine dioxide can also be produced byelectrolysisofachloritesolution:

2NaClO2+2H2O → 2ClO2+2NaOH+H2

A number of products are marketed as “stabilized chlorine dioxide” (SCD). Most of these solutions do not actually contain chlorine dioxide but consist of solutions of buffered sodium chlorite. A weak acid can be addedtoSCDto”activate”itand makechlorine dioxide in-situ without a chlorine dioxide generator. Stabilized chlorine dioxide is used as a broad spectrum disinfectant and anti- microbial; This form of chlorine dioxide is currently being used against bacterial and viral outbreaks including MRSA, Legionella, and Norovirus the use of SCD is effective when the demand for chlorine dioxide is low and when impurities, such as small amounts of sodium, can be tolerated. For application 

requiring above 5 kg day-1 ClO2, chlorine dioxide produced by a generator with either sodium chlorite or sodium chlorate is typically more economical.

Applications of ClO2:

Chlorine Dioxide (ClO2) is used for so many biocidal and oxidative applications, from water deodorization and disinfection to large petrochemical applications. Chlorine dioxide’s unique properties are ideal for solving microbial or compliance-related goals. With a more powerful oxidizing capacity than chlorine, chlorine dioxide is effective over a wide pH range and provides rapid kill for a broad spectrum of organisms.

a) Cooling Towers and process water Loops: ClO2 controls algae, planktonic bacteria, biofilm and scale for maximum efficiency of heat exchangers and ancillary equipment. ClO2 is more stable than other oxidizing biocides and compatible with most water treatment chemistry. This “selective oxidation” makes ClO2 ideal for systems with corrosion problems.

Cooling towers are a prime environment for the build up of microorganisms. Maining control of this build up is essential for efficient operation of the cooling loop. This can be successfully achieved with the use of chlorine dioxide. The microorganisms build slime layers and other colonies, which can result in several serious problems: increased deposits, build up of odors and slime due to the adhesive nature of the biofilm layer, loss of heat transfer due to the insulating nature of inorganic deposits, increased corrosion rates due to “under deposit corrosion,” and increased consumption of power due to the restriction by the deposition. The injection of chlorine dioxide into the recirculation of the cooling towers alleviates these issues and also causes less wear and tear on the equipment. 

b)Potable Water: It is a powerful disinfectant for the treatment of potable water that effectively balances purification performance and disinfection by-product formation. Chlorine dioxide is one of fourEPA-approved disinfectants for drinking water with CT values second only to ozone in biocidal efficacy but without the ozonation by-products or high capital expense. ClO2 is used for both pretreatment and final disinfection of drinking water. In pre-treatment, it effectively removes iron and manganese and promotes flocculation. It also removes taste and odor components as well as halogenated disinfectant byproduct precursors e.g. trihalomethanes (THM’s). In post-treatment, it provides a lasting residual throughout the distribution system. Chlorine dioxide offers utility companies a quick and simple solution to THM and HAA regulatory compliance without costly plant upgrades.

c)Food and Beverage: ClO2 provides excellent microbiological control in flume waters, packaging operations and process disinfection. It is ideal for the washing of cut fruits, vegetables and poultry (FDAapproved) as well as bottling and brewery applications. ClO2 does not react with most “organics” in flume water, which makes it a very effective disinfectant. It also neutralizes foul smelling secondary and tertiary amines formed in the meat packing industry.

d)Odor Control: Chlorine dioxide controls odor in two ways: by controlling microorganisms that form odor- causing hydrogen sulfide and by destroying hydrogen sulfide odors through chemical oxidation. Using an odor scrubber, chlorine dioxide solutions may be added directly to water containing the odorous compounds.

e)Waste Treatment: ClO2 safely oxidizes phenols, cyanides, aldehydes, and mercaptains, reduced sulfur compounds and some pesticides. It is useful in both waste treatment and scrubber systems.

b)Potable Water: It is a powerful disinfectant for the treatment of potable water that effectively balances purification performance and disinfection by-product formation. Chlorine dioxide is one of fourEPA-approved disinfectants for drinking water with CT values second only to ozone in biocidal efficacy but without the ozonation by-products or high capital expense. ClO2 is used for both pretreatment and final disinfection of drinking water. In pre-treatment, it effectively removes iron and manganese and promotes flocculation. It also removes taste and odor components as well as halogenated disinfectant byproduct precursors e.g. trihalomethanes (THM’s). In post-treatment, it provides a lasting residual throughout the distribution system. Chlorine dioxide offers utility companies a quick and simple solution to THM and HAA regulatory compliance without costly plant upgrades.

c)Food and Beverage: ClO2 provides excellent microbiological control in flume waters, packaging operations and process disinfection. It is ideal for the washing of cut fruits, vegetables and poultry (FDAapproved) as well as bottling and brewery applications. ClO2 does not react with most “organics” in flume water, which makes it a very effective disinfectant. It also neutralizes foul smelling secondary and tertiary amines formed in the meat packing industry.

d)Odor Control: Chlorine dioxide controls odor in two ways: by controlling microorganisms that form odor- causing hydrogen sulfide and by destroying hydrogen sulfide odors through chemical oxidation. Using an odor scrubber, chlorine dioxide solutions may be added directly to water containing the odorous compounds.

e)Waste Treatment: ClO2 safely oxidizes phenols, cyanides, aldehydes, and mercaptains, reduced sulfur compounds and some pesticides. It is useful in both waste treatment and scrubber systems.