Bacterial Control

Bacterial control is a crucial part of almost every water treatment strategy and water management regime.  Many bacteria are harmless and can be present in water systems without causing any problems and indeed it is normal for us to find small amounts of bacteria in almost all water supplies we use. Other bacteria, however, are harmful to health and can give rise to a range of symptoms, including skin irritations, migraine, vomiting, diarrhoea and even death. Whilst some groups of bacteria can result in physical damage to plant and equipment, this can take several forms, such as excessive biofilm formation (slime formation), resulting in system blockage and some bacteria can produce strong mineral acids as part of their normal metabolism; which can lead to rapid localised corrosion or pitting of metallic components in the system.

Control of bacteria is therefore a consideration for all system designs, to ensure that human health or system integrity is not endangered. It is an important design requirement that all current legislation is complied with before any system is designed or commissioned.

To give you peace of mind, Hydrotec work continuously with public bodies and other professional organisations alike to ensure that the advice we give is current and fit for purpose.  Most notably these organisations include the Health and Safety Executive, the HPA (Health Protection Agency), WRAS, The Drinking Water Inspectorate, The Society of Public Health Engineers, BSRIA, CIBSE, CIPHE, and The Water Table.  By participating in this way Hydrotec strive to constantly give you the best advice and service. For the control of bacterial populations in hot and cold water services, it is important to follow the prevailing legislation and advice. The current best practice given by the Health and Safety Executive is their document, L8 – Legionnaires’ disease – The control of legionella bacteria in water systems, Approved Code of Practice and Guidance. Fulfilling this guidance will ensure you comply with your legal obligations enshrined by the following statute:

  • Control of Substances Hazardous to Health Regulations 2002
  • Health and Safety at Work etc. Act 1974
  • Management of the Health and Safety at Work Regulations 1999
  • Health and Safety at Work etc. Act 1974
  • Management of the Health and Safety at Work Regulations

 

The Approved Code of Practice (ACOP L8), is designed to control legionella bacteria in particular, though adherence to this advice will control a very wide range of organisms that cause problems in systems. However, every water system must be assessed on its merits and a written risk assessment produced, following on from this assessment the scheme of control can be devised and should be based on one of the following methods:

  • Temperature Control
  • Ultra Violet (UV) / Ozone
  • Chlorine Dioxide Dosing
  • Ionisation

Temperature Control

The temperature control regime relies on providing an environment unfavourable to the growth of bacteria and in particular legionella bacteria. By keeping the cold water cold, bacteria remain viable but dormant and hence pose little threat to man. For hot water systems, temperatures need to be kept hot (generation temperatures need to be at least 60°C with distribution not lower than 50°C). At these temperatures bacteria will begin to die, the higher the temperature, the higher the death rate.  Many systems are successfully operated under this regime, through good design, rigorous execution and regular monitoring are all essential.

Your Hydrotec technical representative will be pleased to provide additional details of how this scheme can work in practice.

Ultra Violet Disinfection and Ozone

The use of Ultra Violet (UV) light to disinfect water systems is a well documented process. It is known that UV light of a critical frequency and magnitude will effectively kill bacteria by severing the DNA strands in the nucleus of the bacteria, in a process biologist’s term, inactivation.  Hydrotec produce a range of WRAS-approved UV biological disinfection systems, you will find further explanation and product detail in the HydroPUR® section of this website.  Ozone is a little used technology for this application due to toxicity, though it can have useful applications elsewhere, for this reason Hydrotec do not currently offer any ozone generating equipment.

Chlorine Dioxide

The use of chlorine dioxide in hot and cold water systems has increased significantly in recent years, due to the unique properties it possesses. First and foremost, it is an excellent biocide, killing virtually all biological species it meets (including legionella) quickly and efficiently. Being a dissolved gas in water, it is a dispersive technology, which means it moves through the entire system, killing both free swimming (planktonic) and biofilm forming (sessile) bacteria.  Finally its use in potable water is approved by the Drinking Water Inspectorate and is an ideal product for bacterial control in water system. For more information on Chlorine Dioxide, see the HydroDOS® section of this website.

Ionisation

This is a technology that relies on the dissolving of silver and copper ions into the water to kill bacteria. There are several shortcomings of this technique listed in the L8 code of practice, principally its unsuitability for use in hard water areas, its loss of efficacy at moderate pH and that it’s only effective against the planktonic or free swimming bacteria, which would only account for a minor percentage of the bacteria in water systems. To compound this, the lack of data for the effect of silver on human health, has lead some bodies to remove silver from the approved list (eg, The Drinking Water Inspectorate on advice from the HSE.)

For these reasons Hydrotec do not offer any products employing this technology.

Design Criteria

The design of every system in every building, must be based on one of these control mechanisms, in order to satisfy the requirements of the code of practice. The selection of the best mechanism for a particular building will vary considerably and depends on many factors. These factors will include:

  • The temperature of operation
  • The application
  • The intended use for the building and hence the population demographic
  • Client preference
  • Health and Safety considerations
  • The size of the building
  • The water system complexity

No doubt there are many other factors that will all play a part in the selection of the most appropriate technology for a particular building. At Hydrotec we have always believed in trying to identify the best technical and commercial solution at the earliest possible time. For this reason your local Hydrotec technical representative (backed by additional UK and international resource) is trained to help guide you through the complexity of the design considerations, to produce a viable, robust and practical scheme, ensuring that the potentially harmful effects of all forms of bacteria in water systems are minimised.