28 June 2024
Eben van Tonder

Introduction

My history with chlorine began in my early 20s when I lived for about eight months in Newhall in Los Angeles with the Luvette family and attended a few business classes at a local community college, College of the Canyons. One of my classes was International Business Administration, where I became familiar with the Uruguay round of the General Agreement on Trades and Tariffs and one of the main disputes between the USA and Europe related to the use of chlorine in the sanitation of chicken carcasses.

Interestingly, washing and sanitizing animal carcasses remained relevant throughout my career. At Woody’s Consumer Brands, I incorporated an acetic acid wash into our operation to mitigate meat of exceptionally low micro standards that the local pork abattoir in Cape Town supplied us with. Years later, in Lagos, the wash of carcasses remains a key strategy of reducing the micro load on the incoming carcasses, and here we opted to use anolyte water produced from an ECA generator. Challenges with water quality prompted me to look very carefully at the matter of the use of chlorine and anolyte.

Oxidation-Reduction Potential (ORP)

The key to evaluating the benefits of anolyte compared to chlorine is to understand ORP. The ORP, or Oxidation-Reduction Potential, measures a solution’s ability to either gain or lose electrons during a chemical reaction. It is expressed in millivolts (mV). ORP values can indicate the disinfecting power of a solution; higher positive ORP values generally correlate with stronger oxidizing properties, which are effective in killing microorganisms. High ORP values (greater than 600 mV) indicate strong oxidizing conditions, typically seen in solutions with high disinfecting capabilities. Conversely, low ORP values (less than 600 mV) indicate reducing conditions, which are less effective for disinfection.

Understanding Anolyte and Catholyte

Anolyte is produced through the electrochemical activation (ECA) process. During this process, water and salt are subjected to an electric current, producing two solutions: anolyte and catholyte. Anolyte is generated at the anode and is characterized by its high ORP, typically ranging from +800 to +1200 mV, indicating strong oxidizing properties. Anolyte water typically consists of hypochlorous acid (HOCl) and hypochlorite ions (OCl-) along with other oxidizing species. These components contribute to its high antimicrobial efficacy, making it highly effective against a wide range of microorganisms, including bacteria, viruses, and fungi, due to its strong oxidizing nature.

Catholyte, on the other hand, is produced at the cathode during the ECA process and has a low ORP, usually negative, indicating reducing conditions. Its composition includes hydroxide ions (OH-) and other reducing agents like sodium hydroxide (NaOH). Although catholyte is less effective as a disinfectant compared to anolyte, it is often used for cleaning purposes due to its alkaline nature but lacks the strong oxidizing properties needed for effective microbial control.

Chlorine: Historical Context and Usage

Chlorine is a chemical element with strong oxidizing properties. In water, chlorine forms hypochlorous acid (HOCl) and hypochlorite ions (OCl-), which are potent disinfectants. The effectiveness of chlorine in killing bacteria, viruses, and other pathogens has made it a widely used agent in water treatment, sanitation, and food processing. Chlorine is commonly used to sanitize food products, including poultry. In the poultry industry, chlorine washes reduce microbial contamination on chicken carcasses by immersing or spraying the carcasses with chlorine solutions to kill harmful bacteria such as Salmonella and Campylobacter.

The use of chlorine in sanitizing chicken carcasses became widespread in the United States in the latter half of the 20th century due to its effectiveness in reducing microbial contamination and ensuring food safety. However, this practice has been a point of contention between the USA and Europe. While the United States accepts and regulates the use of chlorine in poultry processing, the European Union has banned chlorine washes since 1997, citing consumer safety concerns and a preference for maintaining high hygiene standards throughout the entire production process rather than relying on end-of-line disinfection.

USA vs. EU on Chlorine-Washed Chicken

The Uruguay Round of the General Agreement on Tariffs and Trade (GATT), which led to the creation of the World Trade Organization (WTO) in 1995, included discussions on sanitary and phytosanitary (SPS) measures. The EU’s ban on chlorine-washed chicken became a point of contention between the US and the EU. The US has argued that the EU’s ban is not based on scientific evidence of health risks and constitutes a trade barrier. The EU maintains that its stringent regulations ensure higher overall food safety standards and reflect consumer preferences.

Anolyte in the Context of the USA-EU Dispute

Anolyte, with its high ORP and strong antimicrobial properties, presents a viable alternative to chlorine washes. Anolyte is effective in reducing microbial contamination and reverts to normal water over time, leaving no harmful residues. This makes it a safer and more environmentally friendly option compared to chlorine. In the United States, anolyte is gaining acceptance as a disinfectant in various food processing applications, including poultry. It is viewed as an effective and safe alternative to traditional chlorine washes. The European Union has shown a more favourable attitude towards anolyte compared to chlorine, given its non-toxic nature and the fact that anolyte reverts to water, making it more acceptable within the EU’s stringent food safety framework.

ORP Comparison of Chlorine and Anolyte Solutions

Chlorine solutions exhibit varying ORP values depending on their concentration. For instance, a 1g/mL chlorine solution typically has ORP values around 650-750 mV, while a 10g/mL solution shows ORP values of 850-950 mV. A 30g/mL chlorine solution has high ORP values ranging from 1000-1100 mV. In comparison, anolyte solutions also display high ORP values. At a 1% dosage in water, anolyte typically has an ORP of 800-900 mV. Increasing the dosage to 5% raises the ORP to around 900-1000 mV, and at a 10% dosage, the ORP values range from 1000-1100 mV. Neat (undiluted) anolyte can reach ORP values of up to 1200 mV.

This means that anolyte at a 10% dosage compares with Chlorine at a concentration of 30g/mL. At these dosages, Chlorine is responsible for severe pitting.

Pitting Corrosion: Definition and Context

Pitting is a form of localized corrosion that leads to the creation of small holes or pits in a metal surface. This type of corrosion can be particularly insidious because it often goes unnoticed until it causes significant damage. Pitting is typically caused by chloride ions, which are present in many environments, including those where chlorine and anolyte solutions are used for disinfection.

Mechanism of Pitting Corrosion

Pitting begins when the protective oxide layer on the surface of stainless steel is breached, typically by aggressive ions like chlorides. This leads to localized areas where corrosion is concentrated. Once pitting starts, the localized environment within the pit can become increasingly acidic and anoxic, accelerating the corrosion process. This type of corrosion is especially problematic for stainless steel surfaces, which are otherwise known for their resistance to rust and corrosion.

-> Chlorine at a concentration of 30 g/L (30,000 ppm)

Chlorine at this level is highly effective as a disinfectant. It provides rapid and extensive microbial control due to its strong oxidizing properties. This makes it an excellent choice for environments that require stringent disinfection, such as food processing facilities.

However, the high concentration of chlorine also means that it is highly corrosive to stainless steel. Chlorine can penetrate and damage the passive oxide layer that protects stainless steel, leading to pitting corrosion. The high levels of chloride ions in a 30 g/L chlorine solution significantly increase the risk of pitting, especially with prolonged exposure or inadequate rinsing after disinfection.

-> 10% Solution of Anolyte

A 10% solution of anolyte also exhibits strong disinfecting properties. and is generally less corrosive to stainless steel than high-concentration chlorine solutions. While anolyte does contain active chlorine species, the overall concentration of chloride ions is lower, and the presence of reactive oxygen species can help maintain the integrity of the passive oxide layer on stainless steel surfaces. As a result, the risk of pitting corrosion is significantly reduced compared to a 30 g/L chlorine solution.

Using a 10% solution of anolyte is much safer for stainless steel surfaces. It provides a good balance between effective microbial control and material compatibility. While some precautions are still necessary, such as monitoring exposure times and ensuring thorough rinsing, the risk of significant pitting corrosion is much lower. This makes anolyte a far more suitable choice for routine disinfection of stainless steel surfaces in environments where both efficacy and equipment longevity are critical.

Summary and Recommendations

Based on the comparison, both ECA-generated anolyte and chlorine solutions exhibit high ORP values, indicating strong oxidizing and antimicrobial capabilities. However, the specific antimicrobial efficacy and potential for pitting on stainless steel vary with concentration. ECA anolyte is effective across a range of concentrations but is particularly potent at higher concentrations (5% and above), making it suitable for environments with high microbial contamination. Chlorine solutions are highly effective at both 1g/mL and 30g/mL, with the latter providing rapid and extensive microbial control.

In terms of pitting on stainless steel, 1% anolyte poses minimal risk of pitting corrosion, making it suitable for regular use. At 5%, the risk is low to moderate, providing a good balance between effective microbial control and material safety. At 10%, the risk of pitting is moderate, requiring proper handling and exposure times to mitigate potential damage. A 30g/mL chlorine solution, however, poses a high risk of pitting and corrosion, necessitating protective measures for prolonged use.

Continuous production of anolyte offers sustained antimicrobial efficacy due to the consistent generation of active species, making it ideal for applications requiring ongoing disinfection. In contrast, static chlorine solutions are effective initially but require regular maintenance to ensure continued efficacy, best for applications where immediate and potent disinfection is needed.

From a health perspective, ECA-generated anolyte is safe for use in food processing as it reverts to normal water over time, leaving no harmful residues. This makes it suitable for washing equipment and meat carcasses to reduce microbial contamination. Chlorine solutions, while effective, may leave potentially harmful residues on food products, necessitating proper rinsing and adherence to regulatory guidelines to ensure safety.

Conclusion

For applications requiring potent antimicrobial action with minimal risk of stainless steel corrosion, ECA-generated anolyte at moderate concentrations (such as 5%) is a preferable option, especially in high microbial contamination environments like those found in Nigeria. For environments where the highest level of disinfection is needed and material compatibility is less of a concern, high-concentration chlorine solutions can be used with appropriate safeguards to mitigate corrosion risks. Continuous production of anolyte provides a more consistent and sustained antimicrobial effect compared to static chlorine solutions, making it suitable for scenarios demanding continuous disinfection. Additionally, ECA-generated anolyte offers significant health benefits for food processing due to its ability to revert to normal water, ensuring safety for human consumption.

The ongoing trade dispute between the USA and EU over chlorine-washed chicken underscores the importance of finding effective and acceptable disinfection methods. Anolyte represents a promising alternative that could bridge the gap between different regulatory standards and consumer preferences.

References

1. Hricova, D., Stephan, R., & Zweifel, C. (2008). Electrolyzed water and its application in the food industry. Journal of Food Protection, 71(9), 1934-1947.
2. Len, S. V., Hung, Y. C., Chung, D., Anderson, J. L., & Erickson, M. C. (2002). Effects of storage conditions on the stability of electrolyzed oxidizing water. Journal of Food Science, 67(1