Chemical
Well known advantages and disadvantages with using chemicals are as follows:
Advantages
- Better residual effect than thermal.
- Chemical suppliers often subsidise equipment installations.
Disadvantages
- Chlorine (and certain derivatives) gas out at progressively warmer temperatures, making effectiveness uncertain.
- Does not attack biofilm effectively.
- Sometimes suppresses, rather than kills legionella, leading to risk of subsequent outbreaks
- Cost of complying with hazardous substance regulations (COSHH).
- Can be corrosive to pipe work and calorifiers.
- Taste and odour.
- Environmentally poor solution.
- Long term carcinogenic risks.
- Continuing long-term cost commitment.
Summary
On paper, chemicals act as an effective biocide. However, legionella is able to “disappear” in a chemically hostile environment in a number of ways. It can hide in scale and biofilm, neither of which are effectively penetrated by most chemicals. Legionella also invades protozoa such as amoeba, where it hides undetected until the aquatic environment improves for them.
Overall, this is increasingly seen by our customers as an unreliable solution. The ability of the pathogen to hide renders even super-chlorination uncertain. The residual effect, while better than nothing, is insufficient to prevent the re-emergence of the bacteria after chlorination.
Furthermore, environmental considerations work against chemicals. Producing chlorine from brine requires substantial electrical energy input, with an off-site carbon footprint to match. Users of chemicals face increasing legislation, which is anti-chemical on toxicity and hazardous substance grounds, as well as an increasing requirement to respond to environmental concerns.
