Expert report on the dechlorination performance of drinking water from the LaVie process

The so-called drinking water must present a certain number of characteristics in order to be suitable for direct human consumption without risks. While the values of the various monitored criteria may differ between countries, they can nonetheless be classified into three main categories:

• physico-chemical parameters (pH, COD, temperature, conductivity, nitrates, ammonium, chlorides, sulfates, …)
• toxic substances
• microbiological parameters (pathogens such as fecal coliforms).

In France, these criteria can be found in the decree of January 11, 2007, concerning the limits and quality 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.

To ensure the quality of this water, treatments are applied to the extracted water, depending on its sources (surface water, groundwater, desalination, rainwater, reuse) before it can be distributed, ensuring that it remains safe for human consumption up to its points of use.

The required physico-chemical parameters are achieved through the implementation of physico-chemical treatment and separation processes. Disinfection requires the establishment of advanced oxidation solutions such as ozonation, chlorination, and UV light treatment. Regardless of the processes implemented, a chlorination step is very frequently established before distribution to ensure the bacteriological quality of the distributed water up to its point of use due to the residual power of chlorine.
Chlorination processes are very commonly used to disinfect water for consumption (Health Canada, 2009)*. Chlorine has a strong oxidizing power that allows it to quickly kill or inactivate (contact time of about 30 minutes) microorganisms present in the water, and it is generally used in two main forms: solid (tablet) or liquid (bleach or sodium hypochlorite) depending on its large scale of uses (collective or individual). Furthermore, chlorine exhibits a certain stability in water, giving it a residual power; thus, it is important to add sufficient doses of chlorine to ensure both the disinfection of the water on one hand and its residual power during the distribution time on the other hand.

Chlorination disinfection processes present numerous and real advantages in that they are effective, rapid, low-cost, multi-scale, and relatively simple to implement. Nevertheless, they have a number of disadvantages that are important to consider as they may have an effect on human health. Indeed, an overdose of chlorine can lead to reactions between chlorine and other compounds present in the water, particularly organic matter (OM), to form products commonly referred to as “Chlorination By-Products” (CBPs), some of which are considered harmful to human health. Numerous studies (Mouly et al., 2008†) have highlighted the conditions under which such reactions occur, leading to the formation of CBPs. Nearly 600 CBPs have thus been identified, among which major families such as trihalomethanes (THMs) and haloacetic acids (HAAs) represent between 20 and 30% of the total mass of CBPs. Additionally, excessive residual chlorine doses can impart an unpleasant taste to drinking water.

It is therefore important to limit and control the production of these CBPs in treatment chains as well as in distribution circuits. This is primarily achieved through appropriate dosing of chlorine to oxidize organic matter and limit residual chlorine concentrations at the end of treatment. This point is a sensitive issue for chlorination processes and is not always easy to implement in treatment systems, particularly if the resource exhibits variable characteristics and OM content over time. From this perspective, the WHO recommends a free chlorine concentration in treated water distributed between 0.2 and 0.5 mg/l.

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

Ultraviolet (UV) radiation is an electromagnetic radiation whose emission wavelength is shorter than that of visible light and longer than that of X-rays. They represent nearly 5% of the electromagnetic energy emitted by the sun and can be produced by lamps, known as UV lamps. In UV rays, three categories are typically distinguished based on 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 from the sun that reaches the earth belongs to the UVA category.

UV rays have effects on the modification of bacterial DNA, which allows, depending on the exposure time, to kill or inhibit them and thus prevent their reproduction. Finally, it is important to note that UV rays also have effects on the destruction of certain chemical compounds, known as photosensitive, in water or the atmosphere. They can thus contribute to the photodegradation of certain chemical pollutants contained in the water, even at low concentrations.

UV lamp disinfection processes are relatively simple in design as they involve setting up the UV lamp with the water to be treated in what is commonly referred to as the irradiation chamber. These processes are well developed both on an industrial and collective scale as well as on an individual scale due to their ease of use. The literature and industrial developments of these processes are numerous and significant (Oppenheimer et al., 1997)‡, but they rely almost exclusively on the use of UVC radiation lamps.

Regarding the use of UVA lamps (radiation category of the LAVIE® process from the company SOLABLE), to my knowledge, there is currently no industrial development of this type of water treatment lamps, although studies have demonstrated the bactericidal effectiveness of UVA lamps (Hamamoto et al., 2007)§.

In conclusion, UV lamp disinfection processes present a large number of advantages. Indeed, they are simple to use both on an industrial scale and on an individual scale. They do not require the use of chemical reagents or special supports and do not alter the physico-chemical properties of the water to be treated in this sense. Finally, while the initial investment in this type of process may seem higher compared to other processes such as chlorination, its operating cost remains very low with significant lifetimes of the lamps used, making it competitive from this perspective. Nevertheless, there are still some disadvantages to the use of these processes. The bactericidal action of UV lamp processes is not residual, unlike chlorination; thus, its use must be performed as close as possible to the point of consumption and use. Additionally, the use of this type of process requires that the water has sufficient clarity beforehand to not 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 use and to optimize the treatment effectiveness of these processes in the case of a resource characterized by temporal variations in its quality (particularly bacteriological).