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:: Chlorine Dioxide vs. Other Major Disinfectants ::

How does our liquid chlorine dioxide product stand up against the industry standards? This question needs to be examined against a backdrop of advantages / disadvantages of each chemical whilst reviewing, amongst others, the efficacy, ease of usage , toxicity, application levels and cost of equipment for applying the product.

The other major types of disinfectants that are used in the food industry are :

Chlorine
Ozone
Ultra violet light
Quaternary ammonium chloride compounds (QUAT / QAC)
Peracetic Acid (hydrogen peroxide and acetic acid mixtures).
Comparison with other Disinfectants


:: Chlorine ::

We do not need to review, in depth, the chlorine chemistry because we all "know about chlorine". However, it would be beneficial to acquaint ourselves with the major issues which concern people about the continuing use of chlorine as a disinfectant / sanitiser in the food industry.
Chlorine comes in a number of forms:
Chlorine gas
Sodium hypochlorite "bleach"
Calcium hypochlorite HTH tablets / granules
Organo chloro compounds which can release chlorine on contact with water eg dichlorodiisocyanurate.

Irrespective of the form of chlorine, the disinfecting agent is hypochlorous acid HOCl - this is the species that we will dwell upon.

Advantages :
It is a strong oxidant and strong disinfectant.
Depending upon the form it can be easy to use.
It is a most cost effective disinfectant.
It is approved for drinkng water.

Disadvantages: It is corrosive (in all forms).
It is toxic (in all forms) because HOCl can produce, THM's (trihalomethanes, which are carcinogenic) oestrogen mimics, endocrine interceptors, neurotoxins through reaction with organics.
It's efficacy against microbial organisms is very pH dependent :
PH     % HOCl PRESENT IN WATER
6.0   | 100
7.0   | 75
7.5   | 50
8.0   | 24
8.5   | 9
9.0   | 3

The pH in process water in the food industry must be pH 7.0 - 7.5 for chlorine to be cost effective.
It is highly reactive and hence affected by suspended solids and organics in water.
It cab change the taste, odour and taint of food stuffs.
It produces an unpleasant working environment for workers because it has poor stability in water which results in gassing off---being released into air.
It is important to know the difference between "free" chlorine and "combined" chlorine. Free chlorine relates to HOCl in the pH range of 7 - 7.5 and combined chlorine relates to the OCL - ion or reaction solutions eg chloroamines. The latter (OCL- and chloramines) have VERY POOR disinfectant / steriliser capabilities.

The test kits available are HACH, which can be used for "free" and "combined" chlorine levels if the tablets used are changed. The LOVIBOND test only measures "combined" chlorine levels. In the food industry chlorine is needed at 100 - 200 ppm FREE chlorine for it to be effective.

NOTE : 1 kg Chlorine gas is exactly = 1.5 kg HTH is exactly = 13.8 litres hypo
2kg HTH in 10 000 litres of water @ pH 7 will give 100 ppm free chlorine.
If you can smell chlorine in your bath / flume water tank etc it is not working because it has escaped into the air surrounding the bath!! Too many people in the food industry say "when I smell the chlorine, I know that it is working". This is nothing but an urban legend.
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::Ozone::

Ozone (O3) is a gas with very poor solubility in water (0.0001mg/l) which can be produced by electrical discharge through :
Oxygen - which produces nearly 100% ozone
Air - which produces nearly 22% ozone.

It must be noted that the air based generators also produce a number of by-products of nitrogen eg. Nitric acid, nitrogen trichloride and nitric acid. These by products can interfere with the organoleptic properties of the food, fresh produce or processed product.

Advantages:
A very strong oxidant.
A very powerful disinfectant / sterilant.
Very short contact kill times of bacteria, fungi and viruses (in seconds).
Can inactivate all micro-organisms.
Very low running costs (oxygen, air and electricity).
Approved for drinking water.

Disadvantages.
Oxidation of organic matter produces by-products which have been shown to be carcinogenic.
Ozone is not effective against micro-organisms in water with suspended solid loads greater than 10 mg / l (this level is a bad day at a potable water drinking plant).
It is toxic to humans at 0.1 ppm and the smell is irritating at 0.01 ppm in air.
It is corrosive to metals and most plastics.
It has a very low solubility in water and hence it is imperative to have a well designed diffuser to get the ozone gas distributed through the water phase. (If you can see or hear ozone bubbles escaping from the bulk water you will not have ozone in your water phase to do the work you ad been hoping for!). Its residual is measured in seconds to a few minutes in water.
For process water with suspended solids and organics there will be no ozone residual. It will react.
It has no effect against biofilm.
There is a high capital cost of equipment plus oxygen tanks.
NOTE: air generated ozone units are cheap to construct and install by they are not efficient and in the food processing industry they produce nitric acid and other by-products which can impact on the organoleptic properties of he food stuff.
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::Ultra Violet Light::

There are a number of ultra violet (UV) light wave- lengths, which can be used and have shown anti-microbial capabilities. However, it must be stated at the out-set that the UV-C wavelength will not inactivate all bacteria, fungi and viruses because there is a minimum energy intersity requirement for specific micro-organisms. To illustrate this point we show the following table from the paper "Monitoring and Treatment of Recycled Water for Nursery and Floriculture Production" by Martin Meballs etal as the final report for the HRDC Project NY 515.

UV-C LIGHT (uW.sec.per square centimetre)

Phytophthora cinnamomi zoospores 21 000
Phytophthera cinnamomi chlamydeespores 60 000
Pythium ultimum 80 000
Fusarium oxysporum 300 000
Alternaria zinniae 850 000
Treatment of drinking water (typical) 17 000

Advantages:
No operating cost
Quick knock down of micro-organism level.
Easy to install into a food processing facility.
Approved for drinking water.

Disadvantages.
No residual in water.
High maintenance costs.
(UV systems tend to be placed into service and then forgotten. The elements and transmission rates need to be continually monitored so that when they reach a specific level they can be replaced in order to maintain efficiency. Light elements have a definite life span.)
Suspended solids above 10 mg/l diffuses the UV-C light, thereby reducing its efficacy.
It has no impact on bio-film.
(Bio-film can easily grow across UV lights).
High capital costs.
top...


::Quaternary Ammonium Chlordie Compounds (Quat's OR QAC)::

QAC compounds cover four different classes from which there are 292 different chemicals each with different capabilities. This can result in a myriad of formulated products of different types and different concentrations.

As a consequence of the above it is obvious that not all QAC products are the same. There are differing anti-microbial efficacies.

All QAC's are however, surfactants with cationic (positive) charge.

Advantages:
Simple to apply.
Highly concentrated raw materials at low cost.
Non-corrosive.
Generally low toxicity.
A large number of products are bio-degradable.
(There are some QAC products which are not bio-degradable!)
They can operate over a wide pH range.
Approved as a hard surface sanitiser.

Disadvantages.
Generally poor efficacy against gram negative bacteria.
They are film formers which leave a residue on food surfaces or on fresh produce.
Cannot be measured in water easily or accurately and hence will fail HACCP or food safety procedures.
Are surface active agents which cause foaming. This reduces their anti-microbial efficacy.
No impact on biofilm.
It is inactivated by the presence of dirt and anionic products.
No USA or EU approvals for direct use on food or fresh produce.
No approval for drinking water.
NOTE : on Didecyldimethyl Ammonium Chloride (DDAC).
On August 12th 1996 the FDA announced the withdrawal of the petition to allow Didecyldimethyl ammonium chloride to be safely used in, on and for treatment of packaging of food stuffs.
On August 16th 1996 Lonza Inc, the major producer of DDAC withdrew its petition for Didecyldimethyl ammonium chloride as a food additive.
The common products in South Africa like Sporekill, Terminator and Agrisan have didecyldimethyl ammonium chloride as their major compounds.
The reason that companies use DDAC is that it has the most powerful anti-microbial efficacy of all QAC's.
Lastly, DDAC is not bio-degradable and it is a suspect neurotoxin.
General application in the food industry is 200 ppm to 1000 ppm.
At above 200 ppm a water rinse is necessary when used in the food industry.
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::Peracetic Acid::

There are a number of products which fall under the general category of formulations comprising hydrogen peroxide and an organic carboxylic acid eg acetic acid (like Tsunami) and other carboxylic acid (like Vortexx). By stabilising the composition one gets a synergistic affect in terms of anti-microbial efficacy.

Advantages :
Simple to use.
Highly concentrated raw materials at low cost.
Bio-degradable.
Effective as a hard surface sanitiser.
Effective at a broad pH range.

Disadvantages:
Corrosive to equipment.
Dangerous product to handle.
Smells will add taint and odour to foodstuffs or fresh produce.
High level of toxicity.
Cannot be accurately measured in water - will fail HACCP requirements.
No impact on bio-film.
Not approved for drinking water.
No approvals for direct contact on food or fresh produce.
Cannot be used above 0.4%.
(General application level is 0.1% to 0.35%).

There is a class of disinfectants that are mainly used for veterinary and / or medical applications because of their very high efficacy against microbial contamination and these are aldehyde class - formalin and gluteraldehyde. A common product in South Africa is G-Cide - a gluteraldehyde based product. It is a very effective hard surface sanitiser BUT its toxicity to humans is too high to allow it to be used in any direct application on foodstuffs or fresh produce. Stabilised activated gluteraldehyde solutions are widely used in the veterinary and medical fields.

Advantages: High efficacy 1 : 40 - 1 : 200 dilutions on hard surfaces.
Cheap highly concentrated raw materials.
Easy to use.
"Activated" solutions are stable up to 30 days.

Disadvantages:
Corrosive.
Toxic.
Difficult to measure residual concentration in wate.
No impact on bio-film.
No approvals for use as a direct anti-microbial on foodstuffs.
No approval for drinking water.
General application is 0.1% to 5%.
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::Comparison With Other Disinfectants::

Biocide comparison test - concentration required for a > 105 reduction in viable cell counts in 60 secounds.

Journal of Industrial Microbiology
4 (1989) 145 - 154
Ralph S. Tanner

Biocide Active Ingredient (ppm) P. aeruginosa (ppm) S. aureus(ppm) S. cerevisiae(ppm)
Stabilised CLO2 Chlorine dioxide 20000 48 93 95
Chlorine Sodium hypochlorite 52500 1000 1000 1000
Iodophore Complex-bound iodine 180500 (titratable iodine 17500) 440 440 450
Gluteraldehyde Gluteaodehyde 20000 unactivated 2300 1200 620
Gluteraldehyde-phenol Gluteraldehyde activated 20000 1600 2200 18000
Hydrogen Peroxide Hydrogen peroxide 300000 36000 68000 270000
Quaternary ammonium compound Octydecydimethyl ammonium chloride Didecyldimethyl ammonium chloride Etc. 580 140 74
Acidified Quat Quat + phosphoric acid 150 1200 300
Phenol Phenolic compounds 1500 380 190


    


:: Infomation Board ::




Biofilm & Biofouling Manual is now available on our web page. Go to "Downloads" for all the information on Biofirlms & biofouling you need but were afraid to ask.

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