Introduction

SafeSol Ltd and Huwa-San

SafeSol Ltd introduced Huwa-San into the UK legionella control market in 2004 and have used it since that time. The chemical has found steady acceptance since that time as

  1. a competitor to chlorine for one-off water disinfections and
  2. a competitor to chlorine dioxide as a continuous dose chemical.

Like all innovative treatments Huwa-San has been opposed by traditionalists, by companies selling competitor disinfectants, and by companies using other me too silver stabilised hydrogen peroxides.

Huwa-San and Biofilms

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 second blog in a series of 4 that will look at the efficacy of chlorine and chlorine dioxide compared to Huwa-San. This blog looks at why Huwa-San should be preferred over chlorine dioxide as a continuous dose chemical.

[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.

Chlorine Dioxide and Biofilm: The Theory

Chlorine Dioxide v Huwa-San for Biofilm Removal

Chlorine Dioxide is 3-4 times as powerful as bleach as a sanitising agent and is generally effective against all bacteria and viruses. It has been used since the early 1990’s in the UK as continuous dose chemical.  It provides legionella control in buildings where temperature control has proven inadequate.

Experience indicates that Chlorine Dioxide removes and controls biofilm in a water, at much lower dose levels than Huwa-San. Chlorine Dioxide dosed at levels of 1 ppm will often control biofilm in a water system.

Concentrations of Chlorine Dioxide gas as low as 2 mg l−1 have been shown to inactivate more than 5 log CFU cm−2 of Listeria monocytogenes biofilm cells on a meat slicer.

Generally water systems with known biofilm contamination would be dosed at 200 ppm.

Disinfection Levels

If you want to remove a biofilm from a water system you will generally require a 100 times  the concentration of Huwa-San to remove a biofilm compared with Chlorine Dioxide. Then when the biofilm has been removed you need to employ a peroxide concentration of 10-15 times the Chlorine Dioxide concentration to prevent biofilm reformation

The fact above suggest that it is game over for Huwa-San and Chlorine Dioxide Wins….well not quite.

3 Reasons why Huwa-San should be preferred over Chlorine Dioxide as a continuous dose chemical

  • Capital Equipment Cost

  • Breakdown products and Flexibility

  • Corrosion and Maintenance Costs

Capital Costs

Chlorine Dioxide can now be made from preformed tablets or can be provided as a dilute solution. However, generally Chlorine Dioxide is made and dosed on site by reacting sodium chlorite solution with hydrochloric acid solution to form the gas which is then dissolved in water in a mix tank. This solution is then dosed into the water stream. There are variations, for example, acid can be formed by passing water through a cation resin and then mixing this with chlorite solution. Some designs prefer to use an in-line mixer to mix the chlorite and acid streams. The bottom line is that all that Chlorine Dioxide must be dosed accurately and safely. I have witnessed a leak of Chlorine Dioxide. It attracted 7 fire engines and produced a plant room full of foam.

 All this means that a suitable Chlorine Dioxide system may cost £15,000 to £20,000. Huwa-San is dosed using a conventional dosing set costing 25% of this

Breakdown Products and the Inflexibility of Chlorine Dioxide.

The dosing level of Chlorine Dioxide is restricted because of the formation of chlorite and chlorate. In the UK Chlorine Dioxide is dosed to give a residual of 0.5 mg/l (total Chlorine Dioxide + chlorite + chlorate), with a corresponding USEPA level of 1 ppm  This dose level causes no problems because Chlorine Dioxide forms chloride in the body. Increasing the Chlorine Dioxide dose increases the level of break down products. Chlorite and chlorate both have a WHO recommended maximum level of 0.7 ppm. Chlorite and Chlorate can both have an adverse effect on red blood cells. Chlorate can adversely affect the thyroid.

Chlorine Dioxide Dosage Concentrations

The maximum concentration of 0.5 ppm Chlorine Dioxide (0.8 ppm in hospitals with neonate wards) has created problems in water systems with a developing biofilm. In some instances it has proved  impossible to control biofilm in a water system without exceeding the concentration limits imposed on Chlorine Dioxide, chlorite and chlorate Huwa-San has been applied on a number of occasions in systems where Chlorine Dioxide failed to control biofilm.

Drinking Water Approvals

Chlorine Dioxide is accepted by the Drinking Water Inspectorate as a suitable biocide for potable water treatment. Hydrogen Peroxide is not[4],although approved for potable water treatment under PT5  of the Biocidal Products Regulation. Huwa-San has passed all the required tests for the BPR to ensure legionella control and safe human and animal potable water treatment.

Hydrogen Peroxide in water does not make water non-potable the NOAEL (no observed adverse effect level) dose is over 700ppm[5]. The level of Huwa-San used for constant dose in chemicals is 10 ppm peroxide, and this normally gives excellent microbiological control. On the occasions when a positive legionella is recorded the Huwa-San level can be increased to give 50 ppm or even 100 ppm peroxide for a few days to remove any biofilm.

The water is safe to drink throughout the process. Huwa-San is considerably more flexible than Chlorine Dioxide.

[4] The DWI (part of DEFRA) position is that there is a risk to home dialysis units from hydrogen peroxide in potable water. DWI accept that SSHP is used for Legionella control in buildings and advise that they have no jurisdiction over its use in buildings.

There have been 3 occasions in the past when hydrogen peroxide has caused illness and fatality when introduced into a dialysis system. SSHP should not be introduced into any building where there is a risk of it entering a dialysis machine or a hospital laboratory where peroxide can interfere with certain tests.

[5] Hydrogen Peroxide – Oral Risk Assessment Ann Arbor 2010 ( Peer Reviewed)

Corrosivity 

Chlorine Dioxide is corrosive because it is generally made in an acidic environment and it is a strong oxidant. Corrosion in an acidic environment can be countered by inhibiting the acid activator. When the acid activator is not inhibited, system metals will be exposed to acid. Hospital systems have witnessed corrosion and have had to replace parts of the system. Chlorine Dioxide also causes corrosion by oxidation. Work conducted in Italy [6] showed that copper pipes, galvanised pipes and polyethylene pipes were all affected by drinking water levels of Chlorine Dioxide.

Earlier this year I was involved investigating a failure of Durapipe ABS pipe. The internals of the pipework were cracked and whitened following 3 years of Chlorine Dioxide treatment. Failure occurred at stress points in the system. Failure of the ABS is almost identical to the corrosion mechanism witnessed in Reference 6.

[6] https://doi.org/10.3390/ijerph16224582

Conclusion

We now have over 15 years’ experience of continuous dosing of Huwa-San. In hundreds of different situations across several industries (water treatment, animal drinking water, crop irrigation swimming pools) There have been no recorded cases of system corrosion, caused by Huwa-San.

Huwa-San is a better continuous dose chemical than Chlorine Dioxide. It is safer, more flexible, and less corrosive. The capital cost of dosing is around 25% of the corresponding Chlorine Dioxide system.

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