Expert report on the performance of the LaVie process in dechlorinating drinking water

Drinking water must have a certain number of characteristics in order to be safe for direct human consumption. Although the values of the various criteria may vary from country to country, they can be classified into three main categories:

• physico-chemical parameters (pH, TOC, temperature, conductivity, nitrates, ammonium, chlorides, sulphates, etc.)
• toxic substances
• microbiological parameters (pathogens such as faecal coliforms).

For France, these criteria can be found in the decree of 11 January 2007 on the quality limits and references for raw water and water intended for human consumption mentioned in articles R. 1321-2, R. 1321-3, R. 1321-7 and R. 1321-38 of the public health code.

In order to guarantee the quality of this water, treatments are applied to the water withdrawn, depending on its origin (surface water, groundwater, desalination, rainwater, reuse) before it can be distributed, ensuring that it remains fit for human consumption right up to the point of use.

The required physico-chemical parameters are achieved by implementing physico-chemical treatment and separation processes. Disinfection requires the use of advanced oxidation solutions such as ozonation, chlorination and UV light treatment. Whatever the process used, chlorination is very often carried out before distribution to ensure the bacteriological quality of the water distributed up to the point of use, due to the persistent nature of chlorine.
Chlorination processes are very frequently used to disinfect water for consumption (Health Canada, 2009)*. Chlorine has strong oxidising properties, enabling it to kill or inactivate micro-organisms in water quickly (contact time of around 30 minutes). It is generally used in two main forms, solid (tablets) or liquid (bleach or sodium hypochlorite), depending on its wide range of uses (collective or individual). In addition, chlorine has a certain stability in water, giving it a persistent effect. It is therefore important to be able to add sufficient doses of chlorine to ensure both disinfection of the water and its persistent effect over the distribution period.

Chlorination disinfection processes have many real advantages in that they are effective, fast, inexpensive, multi-scale and relatively simple to implement. However, they do have a number of disadvantages that are important to bear in mind, as they can have an effect on human health. An overdose of chlorine can cause the chlorine to react with other compounds present in the water, particularly organic matter (OM), to form products commonly known as "Chlorination By-Products" (CBS), some of which are considered harmful to human health. Numerous studies (Mouly et al., 2008†) have highlighted the conditions under which such reactions take place, leading to the formation of SDCs. Nearly 600 SPCs have been identified, including major families such as trihalomethanes (THMs) and haloacetic acids (HAAs), which together account for between 20 and 30 % of the total mass of SPCs. In addition, excessive doses of residual chlorine can give drinking water an unpleasant taste.

It is therefore important to be able to limit and control the production of these SPCs both in the treatment lines and in the distribution circuits. This is essentially achieved by appropriate chlorine dosing to oxidise organic matter and limit residual chlorine concentrations at the end of treatment. This is a sensitive point for chlorination processes and is not always easy to implement in treatment systems, particularly if the characteristics and OM content of the resource vary over time. From this point of view, the WHO recommends a free chlorine concentration of between 0.2 and 0.5 mg/l in distributed treated water.

In recent years, UV light disinfection processes have been developed and marketed. They are based on the principle that UV rays have a significant bactericidal effect.

Ultraviolet (UV) radiation is electromagnetic radiation with an emission wavelength shorter than that of visible light and longer than that of X-rays. It accounts for almost 5 % of the electromagnetic energy emitted by the sun and can be produced by lamps, known as UV lamps. UV rays are classically divided into three categories according to their wavelength: UVA (400-315 nm), UVB (315-280 nm) and UVC (280-100 nm). It should be noted that due to the absorption of UV rays by the ozone layer in the atmosphere, almost all (95%) of the UV light coming from the sun and reaching the earth is in the UVA category.

UV rays modify the DNA of bacteria, killing or inhibiting them, depending on the length of exposure, and thus preventing their reproduction. Finally, it is important to note that UV rays also have the effect of destroying certain chemical compounds, known as photosensitive compounds, in water or the atmosphere. They can therefore play a part in the photodegradation of certain chemical pollutants contained in water, even in low concentrations.

UV lamp disinfection processes are relatively simple in design, as they involve placing the UV lamp in a small reactor with the water to be treated in what is commonly known as the irradiation chamber. These processes have been developed both on an industrial and collective scale and on an individual scale, mainly because they are so easy to use. The literature and industrial developments of these processes are numerous and significant (Oppenheimer et al., 1997)‡ but they are based almost exclusively on the use of UV radiation lamps of the UVC category.

As far as the use of UVA lamps is concerned (radiation category of the LAVIE® process from SOLABLE), although to my knowledge there is currently no industrial development of this type of water treatment lamp, work has nevertheless proven the bactericidal effectiveness of UVA lamps (Hamamoto et al., 2007)§.

In conclusion, UV lamp disinfection processes offer a large number of advantages. They are easy to use on both an industrial and an individual scale. They do not require the use of chemical reagents or special media, and therefore do not alter the physico-chemical properties of the water to be treated. Finally, while the initial investment in this type of process may seem higher than for other processes such as chlorination, its operating cost remains very low, with long lifetimes for the lamps used, making it competitive from this point of view. However, there are still a number of disadvantages to using these processes. Unlike chlorination, the bactericidal action of UV lamp processes is not long-lasting, so they should be used as close as possible to the point of consumption and use. In addition, this type of process requires water of sufficient clarity beforehand, so as not to limit the transmission of UV radiation in the water. Finally, it is difficult to immediately assess the effectiveness of the treatment by measuring a residual, as in the case of chlorine, and to optimise the treatment effectiveness of these processes in the case of a resource characterised by temporal variations in its quality (particularly bacteriological).