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Disinfectants – A Comparison

Chlorine (Cl)

A greenish–yellow gaseous element which combines directly with nearly all elements, is two and one half times as heavy as air, has an intensely disagreeable suffocating odor and is exceedingly poisonous. It is found commonly as NaCl (solid or seawater).

Advantages

• Strong oxidant, disinfectant and bleaching agent
• Eliminates tastes and odors
• Featured with after-effect
• Controls growth of algae, biological slimes and microorganisms
• Decomposes organic contaminants (phenols...)
• Oxidizes iron and magnesium. Decomposes hydrogen sulfide, cyanides, ammonium and other nitrogen compounds

Disadvantages

• Chlorine is a respiratory irritant. The gas irritates the mucous membranes and the liquid burns the skin. As little as 3.5 ppm can be detected as an odor, and 1000 ppm is likely to be fatal after a few deep breaths
• Special requirements for transportation and storage
• Potentially dangerous in case of a leak
• Formation of disinfection by-products such as chloroform. The MAC in water will be increased in the near future from 60 mkg/l up to 60 mg/l because there is no proof of direct action of the chloroform on DNA.

Chlorine Dioxide (ClO2)

Chlorine dioxide is a synthetic yellowish-green gas with chlorine-like odor. ClO2 is unstable as a gas and will undergo decomposition into chlorine gas (Cl2), oxygen gas (O2) and heat. However, ClO2 is stable and soluble in an aqueous solution. For example, solutions of approximately 1% ClO2 (10 g/L) may safely be stored if the solution is protected from light and kept chilled. In solution, ClO2 exists as a true gas.

Advantages

• The most effective disinfectant and strongest oxidation agent among all chlorine-containing ones
• Low dosing
• No formation of chloramines
• Formation of trihalomethane is not facilitated
• Eliminates phenols which is the source of unpleasant taste and odor Effective oxidant and disinfectant for all types of microorganisms, including cysts, (Giardia, Cryptosporidium) and viruses
• No formation of bromides from bromates
• Removes iron and magnesium from water by oxidation and precipitation of oxides

Disadvantages

• On-site generation only
• Requires transportation and storage of chemicals
• No formation of non-organic by-products
• Forms chlorates and chlorite ions
• The instability of ClO2 has an important consequence. It negates the possibility of creating and transporting cylinders or rail cars of the gas

Hypochlorite (NaClO)

Hypochlorite is a chemical compound, a colorless, transparent liquid. It is dissolved in cold water and decomposed by hot water or carbon dioxide. As an excellent chlorine sterilizer, it serves as a strong oxidizer and bleaching agent.

Advantages

• Applied in liquid or granulated forms (trade concentration - 10-20%), electrochemically available on-site
• Effective against most of the pathogenic microorganisms
• Relatively safe during storage and use
• No transportation and storage of chemicals if generated on-site

Disadvantages

• Ineffective towards cysts (Giardia, Cryptosporidium)
• Loses effectivity during long-term storage
• Dangerous chlorine-gas emissions during storage
• Forms trihalomethane
• Iimmediate use is recommended if generated on-site. In case of storage, special measures are made to purify the initial water from heavy metal ions. When generated on-site, NaCIO solution with an active chlorine concentration less than 450 mg/l will not form chlorates during storage

Chloramine (NH2Cl)

Chloramine is formed through the reaction of dissolved chlorine gas (forming hypochlorous acid) and ammonia in tap water. Chloramine is a term that actually describes several related compounds: monochloramine NH2Cl, dichloramine, NHCl2 and trichloramine, NCl3. Chloramine (monochloramine) is a toxic substance created by the chemical reaction of ammonia and sodium hypochlorite (chlorine bleach) under alkaline conditions. It is a yellow liquid at room temperature. It is commonly used in low concentrations as a disinfectant in municipal water systems as an alternative to chlorination. Unlike chlorine, chloramine cannot be removed from water by boiling, or by letting an open container of water stand to dissipate chlorine. It can only be neutralized, or removed with specific treatment methods.

Advantages

• Stable and long-time after-effect
• Facilitates removal of foreign taste and odor
• Reduces the level of trihalomethane and chlorine-organic acid generation
• Prevents formation of biological slimes in water distribution systems

Disadvantages

• Weak disinfectant and oxidation agent compared to chlorine
• Ineffective against viruses and cysts (Giardia, Cryptosporidium)
• Considerable dosing and prolonged contact time are required for disinfection
• Danger to patients using dialyzers, since it penetrates dialyzer membranes and effect erythrocytes
• Forms nitrogen-containing by-products

Ozone (O₃)

Ozone (O₃ : 3 oxygen atoms) occurs naturally in the atmosphere. Ozone (O₃) is an allotrope of oxygen, the molecule consisting of three oxygen atoms instead of the more stable diatomic O₂. Ozone is a pale blue gas at standard temperature and pressure. It forms a dark blue liquid below -112 °C and a dark blue solid below -193 °C. Ozone is a powerful oxidizing agent. It is also unstable, decaying to ordinary oxygen through the reaction. This reaction proceeds more rapidly with increasing temperature and decreasing pressure.

Advantages

• Used for several decades in some European countries for the purpose of disinfection, color elimination, taste and odor control
• Strong disinfectant and oxidation agent
• Very effective against Giardia, Cryposporidium and any other pathogenic microflora
• Facilitates removal of turbidity from water
• Does not form chlorine containing trihalomethanes

Disadvantages

• Ground level ozone is an air pollutant with harmful effects on lung function
• Forms byproducts, including: aldehydes, ketones, organic acids, bromine-containing trihalomethanes, (bromoform inclusive), bromates (in presence of bromides): peroxides, brom-acetic acid
• Necessitates the use of biologically active filters to remove by-products
• Does not ensure residual disinfection effect
• Requires significant initial expenses for the equipment
• Considerable expenses for operators` training and installation support
• When reacting with organic compounds, ozone disintegrates them into smaller components, which could become a feeding media for microorganisms growth in water distribution systems

Ultraviolet (UV)

The name means "beyond violet" (from Latin ultra, "beyond"), violet being the color of the shortest wavelengths of visible light. Ultraviolet (UV) radiation is electromagnetic radiation of a wavelength shorter than that of the visible region, but longer than that of soft X-rays.
The Sun emits ultraviolet radiation in the UVA, UVB, and UVC bands, but because of absorption in the atmosphere's ozone layer, 99% of the ultraviolet radiation that reaches the Earth's surface is UVA.

Disinfecting drinking water: UV radiation can be an effective viricide and bactericide. Disinfection using UV radiation was more commonly used in wastewater treatment applications but is finding increased usage in drinking water treatment. It used to be thought that UV disinfection was more effective for bacteria and viruses, which have more exposed genetic material, than for larger pathogens which have outer coatings or that form cyst states (e.g., Giardia) that shield their DNA from the UV light.

Advantages

• No special requirement for storage and transportation
• No formation of by-products

Disadvantages

• No residual effect
• Ineffective towards cysts (Giardia, Cryptosporidium)
• Expensive in equipment and maintenance
• High operational (power) costs
• Disinfection depends on water turbidity, its hardness and precipitation of organic impurities caused by sediments on the bulb surface
• Power supply deviations affect the wavelength
• Since microorganisms can be shielded from ultraviolet light in small cracks and other shaded areas, however, UV lamps are used only as a supplement to other sterilization techniques

Reverse Osmosis (RO)

Reverse osmosis is the process of pushing a solution through a filter that traps the solute on one side and allows the pure solvent to be obtained from the other side. More formally, it is the process of forcing a solvent from a region of high solute concentration through a membrane to a region of low solute concentration by applying a pressure in excess of the osmotic pressure . The membrane here is semipermeable , meaning it allows the passage of solvent but not of solute. The membranes used for reverse osmosis have no pores, the separation takes place in a dense polymer layer of only microscopic thickness. In most cases the membrane is designed to only allow water to pass through. The water goes into solution in the polymer of which the membrane is manufactured, and crosses it by diffusion. This process requires that a high pressure be exerted on the high concentration side of the membrane, usually 5 MPa - 20 MPa (50 bar - 200 bar ).

Features
This process is best known for its use in desalination (removing the salt from sea water to get fresh water ) and has been used in this way since the early 1970s

Disadvantages

• Water is pressed through special filter membranes. These membranes have mesh sizes of approx. 0,1 micrometer (0,001 mm). That means that all minerals are extracted from the water since minerals are bigger than 0,1 micrometer
• Distilled stale-tasting water resulting from RO is not enjoyable to drink anymore
• The neutral pH-value in the water can be only re-established by adding minerals
• After the RO-process, the water must be disinfected

Silver

A fully different effective mechanism for drinking water disinfection is the oligodynamic efficacious silver. The method is mainly submerging silver ions in water for disinfection.

Advantages

• Silver water has curative properties against diseases
• Disinfects drinking water for a longer period of time

Disadvantages

• Long reaction time
• Chloride in water extends contact time to achieve disinfection effects

Electro-Chemical Activation Process (ECA)

Process used in the production of a disinfectant acidic-water without the use of chemical additives. Salt solution and electricity are used and separated by two electrodes in a Diaphragmalyser to produce two solutions: acid solution and alkaline solution.

Advantages

• Production of superior quality drinking water in conformity with the European Union Drinking Water Directive.
• Water is safe to drink for a longer period of time if appropriately treated
• Short-term amortization, long-term savings
• The process preserves all minerals in the water, resulting in a natural and pure water taste - no more chlorine taste
• The water does not loose its vitality. No essential ingredients are eliminated, filtered out or destroyed. All mineral contents in the water remain during and after the process
• Magnesium as an important and essential mineral in water is preserved. All enzymes are preserved through Ion-Exchange-Method, since only Ions are exchanged through the membranes.
• Automatic production of acid-water and activated alkaline water; no acute or chronic toxicity when diluted in water
• User-friendly, very easy to operate, no qualified personnel required
• Conveniently run, monitored and maintained via internet (Internet access presumed).
• Easy installation; wall-mounting and requires minimum space; size of an equipment is as big as a shoe cabinet
• Environment-friendly technology, solutions are 100% biodegradable
• Powerful disinfectant and oxidation agent; used for general disinfection in households, agricultural farms, hospitals/clinics and buildings
• Effectively eliminates bad tastes and odors
• Removes biofilms in flowing water and pipes
• Significantly less formation of chlorine compounds, halogens and TMT
• No toxic by-products: clorites (ClO2) and clorates (ClO3)
• No transport or storage problem
• Easy and safe storage and handling; no special protection required

Disadvantages
Installation rooms will need ventilation systems to avoid fumes

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