Water sanitisers

There are many brands of water sanitisers available to the poultry producer, although they arepredominantly derived from only a few chemical groups. In some cases, water may need treatmentprior to sanitation.

The choice of sanitiser should primarily be based on efficacy, followed by other factors suchas application method, cost and safety. Poultry producers are not specialists in the science ofsanitisers and are thus usually dependent on company technical advisors, veterinarians or salespeople to provide the necessary information.

Some sanitisers are marketed based on information only about their effectiveness to inactivatebacteria, usually under non-commercial situations such as distilled water with serum. The failure toproduce data on viral inactivation is usually because such testing is expensive and technically difficultto undertake. The major types of water sanitisers that are available include the following categories:

• the halogens—including chlorine, bromides and iodines (iodophors), chloramines, and potassium permanganates
  
  
• other oxidisers, including chlorine dioxide, hydrogen peroxide, ozone and peracetic acid
  
  
• organic acids, usually short chain fatty acids
  
  
• quaternary ammonium compounds
  
  
• ultraviolet (UV) light
  
  
• other products such as citric acid, copper-silver ionisation, etc.
  
  

The more commonly used water sanitisers are discussed below.

4.2.1 Halogens

Of these, chlorine (hypochlorous acid/chlorite ion) is the most commonly recognised and used.The activity is mediated by hypochlorous acid produced at acid pH and the efficacy of chlorinesdeclines as pH increases (optimum around pH 6.7). Hypochlorous acid denatures proteinsby oxidation and it is this property as an oxidiser that confers its biocidal activity. Chlorineis available in liquid form as sodium hypochlorite and in solid form as calcium hypochlorite.Sodium hypochlorite is usually available at a concentration of 10 to 12% (De Benedictis, Beato,& Capua 2007). Chlorine (usually as liquid hypochlorite) has a broad spectrum of activity, isminimally affected by hard water and acts rapidly. Its use is limited by its corrosive nature.The efficacy of chlorine is affected by organic material and turbidity, UV light and heat andits limited residual activity. Chlorine has a very low cost and application systems involveonly small capital outlay.

While some earlier reports had demonstrated the effectiveness of chlorine on AI virus, it wasnot until 2007 (Rice, Adcock, Sivaganesan, Brown, Stallknecht, & Swayne 2007) that specific workwas undertaken demonstrating chlorine’s effectiveness against H5N1. Studies demonstrated thatonce the chlorine demand was met, the maintenance of free residual chlorine at around 1 part permillion (ppm) was sufficient to inactivate the virus.

Iodines, or formulated variations such as iodophor, are similar in effectiveness to chlorine,showing some advantage in ability to cope with organic load.

Bromine is more stable than chlorine as it has a higher evaporative point. Bromine continuesto be effective even after reacting with organic compounds. Hypobromous acid is the activeform that inactivates the pathogens. After reacting, the hypobromous acid is reduced back tobromide ions. The addition of an oxidizer will convert the bromide back to hypobromous acid.This is done by adding fresh oxygenated water, for example, in an evaporative cooling padrecirculating water tank.

4.2.2 Other oxidisers

Amongst oxidisers, chlorine dioxide is becoming popular for water sanitation in the poultryindustry. It is broad spectrum, sporicidal and fast acting. It disinfects by oxidation but does notchlorinate. It is also significantly more resistant than chlorine to organic quenching and lessaffected by pH. This allows for more effective sanitation of water using levels of chlorine dioxideas low as 0.1 ppm.

Chlorine dioxide assists in reducing biofilm build-up in drinker systems and, unlike halogens, doesnot form complexes like chloramines which are potentially carcinogenic. The cost of the chemicalis much higher than chlorine and there is the added requirement for a chemical activator such asphosphoric acid. Application systems are also significantly more expensive than those required forchlorine. With new technology, the lower cost precursor compound sodium chlorite can be used togenerate chlorine dioxide using an electro-discharge plate that generates hydrogen gas. The capitaloutlay for this equipment is high.

Hydrogen peroxide has similar inactivation properties to chlorine dioxide and can be used in thesolution or vapour phase. However it is corrosive, inactivated by heat and organic material, andneeds to be used at high concentrations. This oxidiser also has limited residual activity.

Peracetic acid is similar in activity to chlorine dioxide and is effective in the presence of organicmatter. Compared with chlorine, its limitations—besides cost—are that it is corrosive to soft metals,unstable at high ambient temperatures and is an irritant, particularly in its concentrated form.

Ozone is generated from electrical discharge units and bubbled into the water supply. Ozone sanitises water either by direct oxidation and disruption of cell membranes of microbes bymolecular ozone or by free radical-mediated destruction of microbes. Also, through indirectoxidation reactions of ozone, the ozone molecule decomposes to form free radicals which reactquickly to oxidise organic and inorganic compounds. Generally the efficacy and activity of ozoneare similar to chlorine dioxide. Set up capital costs can be high, as are maintenance costs due todischarge tubes requiring replacement every few years.

4.2.3 Ultraviolet light

UV light is used minimally in the poultry industry and generally for the sanitation of low volumesof clean water in hatchery mister sprays. UV light has proved unable to inactivate HPAI virus after45 minutes exposure (De Benedictis, Beato, & Capua 2007). UV water treatment is not effectivefor sanitising surface water unless the water is clean. It has a relatively low cost but its usefulnessis limited under situations where there are very high volumetric demands and it has no residualactivity. Its efficacy is not affected by pH.

4.2.4 Organic and inorganic acids

Acids have a high viricidal activity and through the correct choice of acid, or acid mixture,this class of disinfectants can be used for several purposes from liquid effluent treatment todecontamination of structures. There are two categories of acids that can be used in disinfectionprocedures: organic acids (formic, citric, lactic, mallic, glutaric and propionic acids) and inorganicacids (nitric, hydrochloric, sulphuric, phosphoric, sulphamic acids). Both are effective, especiallyagainst viruses that are sensitive to low pH, but they are generally slow-acting (Jeffrey D.J. 1995).Inorganic acids are able to inactivate viruses only through decreasing pH values. These acids aremore typically used in research, for example, in sanitising clean water for specific pathogen free(SPF) birds. In contrast, organic acids inactivate viruses also through the interaction of lipophilicstructures with membranes of enveloped viruses (Haas et al. 1995).

Organic acids were originally introduced to the poultry industry as an aid to improving flockperformance rather than as a generic water sanitiser. Their ability to inactivate microbialcontamination varies depending on the agent. Their cost is high when compared to chlorine,and high levels of organic acids in poultry drinking water may decrease water intake andreduce performance. This latter effect is due to the organic acids affecting the taste of the water.

Acidifiers do not replace sanitisers but are used to reduce high water pH to levels of 6.0 to 6.7 toimprove the efficacy of sanitisers such as chlorine.

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