Introduction

This blog looks at Huwa-San’s stability in water and offers the water treatment market a biocide that provides long term protection of water systems. The addition of Huwa-San to water in unoccupied buildings means considerably less flushing, reduced testing and improved safety. Huwa-San added to building water systems prior to shutdown will protect unused water systems from microbiological growth. It could, for example, be an alternative to flushing during lockdown, school holidays and for any water system which is temporarily out of use.

Comparing Huwa-San with Hydrogen Peroxide

This blog is written by our technical director Bob Wilson, who has been working with oxidising biocides since the 1970’s. This includes working with and studying Huwa-San[1], chlorine and chlorine dioxide. He has been involved in several expert witness cases including the Edinburgh Legionella Cooling Tower Outbreak.

It is the third blog in a series of four that will look at the stability of Huwa-San, silver stabilised hydrogen peroxide (S.S.H.P.s) compared with normal hydrogen peroxide and the benefits it can bring.

[1] The stabilisation of Huwa-San allows it to delay the reaction between chloride in water and silver ion. This stabilisation is unique to the Roam Technology product, differentiating it from other SSHP formulations.

Huwa-San: The Pros

 Huwa-San is Far Better than Hydrogen Peroxide.

 Huwa-San has s three distinct advantages over ordinary hydrogen peroxide.

Killer of Bacteria, Viruses and Mould

  • It is a more effective killer, particularly where the microorganism produces a lot of catalase (Huwa-San is 10 times more effective than hydrogen peroxide on legionella (low Catalase producer) and 50 times more effective on pseudomonas (high Catalase producer)

Efficient Biofilm Remover

  • Huwa-San is an effective biofilm remover – This is almost certainly because of the targeting /catalytic effect of the silver ion. Ordinary hydrogen peroxide is relatively ineffective as a biofilm remover. My previous posts have demonstrated that chlorine is also an ineffective biofilm remover, and that Huwa-San has many benefits over chlorine dioxide as a biofilm treatment chemical.

Great Stability in Water

  • Arguably the greatest advantage of Huwa-San over ordinary hydrogen peroxide is the stability of the silver stabilised product over ordinary peroxide. This blog focusses on product stability- an aspect of the product that is often forgotten and a property that many have failed to take advantage of.

Huwa-San TR-50 (50% v/v hydrogen peroxide is completely stable in an unopened drum -generally for more than 5 years. It is the stability of the product in water that is important and needs to be better utilised.

The Role of Silver Ion in Huwa-San

The stability of hydrogen peroxide is obviously affected by the presence of silver ion. The silver ion exerts electronic attraction and also influences the hydrogen bonding between peroxide molecules. The attraction between the silver ion and the hydrogen peroxide means that hydrogen peroxide can take advantage of the targeting effect of the silver on any microorganism. Silver ion is electronically attracted to certain groupings (generally thionyl) on the exterior cell wall of a microorganism and the attraction between silver and hydrogen peroxide draws the peroxide on to the microorganism. Following the death of the microorganism, the hydrogen peroxide molecules quickly regroup around the silver ion ready for the next challenge. This mechanism coupled with the fact that silver ion is a true catalyst means that biofilms can be attacked and destabilised[1]

Please see diagram 1.

[1] This mechanism is explained in much greater detail in the article Silver Stabilised Hydrogen Peroxide – The Role of Silver Ion. Water line – Autumn 2018.

How Huwa-San Works: Diagram 1

Huwa-San Versus Hydrogen Peroxide

  • 3% hydrogen peroxide solution – Huwa-San TR3 will be stable for at least one year in the bottle.

Compared to

  •  3% solution of ordinary hydrogen peroxide will  reduce to 2.5% over one year
  • 1000 ppm solution of ordinary hydrogen peroxide will disappear completely from water within a few days

Compared to

  • Independent tests show that 1000ppm hydrogen peroxide based on Huwa-San fell to 900 ppm after one month.

A 75 ppm solution of hydrogen peroxide based on Huwa-San fell to 46 ppm after one month

Huwa-San dosed at 100ppm peroxide for standard disinfection of a water system with a 24 hour retention time decays as water is used and replaced by fresh water. Tests have shown that after 1 day the hydrogen peroxide level is 50 ppm. The residual drops to <3 ppm after 5 days.

I want to look at the ways that Huwa-San’s stability can be exploited.

Huwa-San as a Cooling Water Biocide

Huwa-San, though used successfully on several occasions, is barely recognised as a cooling water biocide. The main reason for this is its per litre cost compared with other oxidising biocides. Superficially, the cost of a chlorine based cooling water programme is between 10% and 15% of a Huwa-San based programme.  Apart from Huwa-San’s superior biofilm removal capability compared with chlorine, it is important to note that Huwa-San stays in the cooling water. It is not removed by high temperature, the airflow through the tower or by the reaction with ammonia. While the chlorine residual in the water flow to the tower is continually having to be made up the level of Huwa-San does not. In clean towers, for example, those associated with air conditioning the cost of using Huwa-San as a biocide is comparable with the cost of using Chlorine.

Huwa-San, a much more powerful biofilm remover than chlorine should also be considered for off- Line cooling tower disinfection.

Huwa-San in the Laboratory

One of the regular uses of Huwa-San has been as a disinfectant in water baths. It has been shown to be more stable, (therefore more cost effective) and in addition much less aggressive than peracetic acid based formulations.

Reduce water usage whilst protecting against legionella bacteria

Domestic Water Systems

Huwa-San is widely used for one off disinfection and for continuous dosing in buildings. Experience shows that it has many advantages over chlorine, it is not broken down at calorifier temperatures and therefore disinfects calorifiers at operating temperature. While Huwa-San is stable in cold water there can be some reduction in Huwa-San concentrations due to the high organic load within the calorifier. During continuous dosing of a domestic hot water with Huwa-San the concentration in the hot water is generally lower by 1 or 2 ppm than the cold water concentration.

  • Emergency/Isolated Shower Units

Shower units in the field with their own dedicated supply tank, have the water dosed to a level of 1000 ppm hydrogen peroxide. This will require less maintenance as the water will continue to be sterile for around 30 days.

  • Shutdown Water Systems

This is a use that is particularly pertinent during lockdown when buildings have been closed for lengthy periods. It is a technique that I have used where water systems are not drained down, for example, for schools over the summer months and hostels over the winter months. Prior to closure of the building the complete water system is cleaned (where required) and disinfected with four times the normal dose of Huwa-San so that 400 ppm hydrogen peroxide is left throughout the system.

Huwa-San has been shown to be stable for at least 6 weeks based on it half life in water. Flush outlets after week 3 to ensure there is still a healthy peroxide residue at the taps.

Conclusion

This use of Huwa-San will greatly reduce water losses (something which will become more important as water costs increase), reduce flushing frequency and testing and maintains system cleanliness throughout the shut-down period.

There will be other opportunities to take advantage of a stable biocide that will prevent biofilm formation in a water system. If you have any further ideas on how to utilise Huwa-San’s excellent stability it would be great to hear from you.

SafeSol have worked with Huwa-San technology for over 20 years and have more than 75 years experience in water treatment. We are happy to help with any queries and provide technical support .

Call 0191 4478008 or info@safesol.co.uk