Have we really sorted Legionella Control?
Remote Temperature Monitoring
Two different aspects of Legionella control have come to prominence in recent months. The first is remote temperature monitoring. The placing of temperature probes at the key points in a domestic water system and being able via a data logger to relay information back to interested parties. It’s hardly new technology as the technology was available to the petrochemical industry when I was working at BP in the 1960’s. The technology may improve monitoring efficiency and accelerate remedial action. It may even slightly reduce legionella risk in a few situations. It may reduce monitoring costs.
Good temperature control is designed to ensure that any legionella bacteria entering a water system cannot multiply, because the water temperature will not permit it.
The Use of Thermostatic Mixer Valves
The second aspect of Legionella control that has come to prominence is the use of TMV’s to control temperature or more precisely where should we use TMV’s and where should we not.
TMV’s in my opinion represent a failure of the water treatment industry. The rising cost of energy today makes a policy of heating water to 60o C to kill legionella and reducing it down to 40o C questionable. Water treatment companies are unwilling to use continuous dosing of an oxidising biocide to combat legionella because most are far more comfortable with carrying out temperature monitoring. Setting up, monitoring, and reducing hot water temperature is beyond the competence of many involved in water treatment today.
Cost Savings With Constant Biocide Dosing And Temperature Reduction
I find that any proposal to reduce temperature and install oxidising biocide dosing, is met with arguments of how it will not really save money. (These calculations never account for the £600 cost of each TMV). In many cases, especially in larger buildings, there will be a cost saving without factoring in the cost of TMV’s where constant dosing is introduced.
In spite of the increased cost of energy new buildings continue to heat water to 60oC and install TMV’s instead of installing a system that heats domestic water to 40oC, has a biocide dosing system, monitoring system and no TMV’s.
The Continuous Dosing of Biocides
The continuous dosing of a biocide to a complex water system can be challenging. The challenges usually occur at the commissioning stage where biocide residuals can disappear because of organic material, metal ions or preformed biofilms in systems. Overcoming early issues will require additional on-site time until a biocide residual can be established and maintained. It is easy to forget that the use of TMV’s to control temperature presented early problems as seals were found to be a source of biofilm formation and the presence of legionella in water systems.
The water treatment industry fails to understand oxidising biocides. Chlorine (even with its 700 breakdown products – some carcinogenic) continues to be used for disinfection by many water treatment companies even though it is well established that chlorine will not remove a mature biofilm. This is surely wrong when Legionella Pneumophila come from amoeba associated with biofilm.
7 Reasons why we still get legionella bacteria even in “L8 compliant premises”
- Not enough focus on the analysis of mains water. You can tell a lot about possible scale and corrosion and subsequently deposition in a system. You can also learn, a lot from the microbiology of the incoming water.
- The belief that a few temperature measurements in a month tells you that a system always meets control requirements. Remote continuous monitoring has taken too long to be introduced.
- The belief that chlorine is regarded as a good legionella biocide when it is known that it cannot remove or treat biofilm.
- The use of single treatment showerhead cleaners in hard water areas. Some have no proven efficacy against biofilm. Many behave like chlorine and only affect the outer layers of a biofilm.
- A belief that all silver stabilised hydrogen peroxides are the same. They all contain 50 % v/v hydrogen peroxide and 300 ppm to 500 ppm silver, but their effectiveness depends on how the silver / chloride reaction in water is prevented. There is a big difference in how these products are stabilised. Some are ineffective against biofilm.
- The continuous dosing of a low-level oxidising biocide would change how most systems are controlled. Most water treatment / hygiene companies do not have the competence to use biocide control. The advantages are no TMV’s, therefore no TMV servicing, and it costs less).
- The water treatment industry are followers and not leaders. That’s why we heat our water to 60oC and then use TMV’s to reduce temperature the temperature to 40 o Great business for sellers of TMV’s. Why are there very few implementations of a water treatment solution?
