LCA av dricksvattendesinfektion
en jämförelse av klor och UV-ljus
Disinfection methods for drinking-water produced at the two water works of Stockholm Water Co are compared in this study. Three different nethods are compared; disinfection with chlorine gas, disinfection with sodium hypochlorite and disinfection with UV-light and monochloramine. The method used is Life cycle assessment, LCA. LCA is defined as the compilation and evaluation of the inputs, outputs and potential environmental impact of a product system shroughout its life cycle. The environmental burden is compared for the three different disinfection methods. Potential health effects and the working environment are also included.
One disadvantage with chlorination is the production of unwanted by-products when the free chlorine reacts with organic matter. These by-products, e.g. trihalomethans, THM, have shown to bee carcinogenic. This was one of the reasons that contributed to the changeover to disinfection with UV-light, at one of the two outgoing lines at Lovö water works. The UV-disinfection makes it possible to ure half of the ordinary dose of chlorine, it also lowers the amount of THM in the drinking water with 90%. (Blomberg et al. 2001)
UV-disinfection also led to increased bacterial reduction compared to chlorination. Another positive aspect is that the risks with handling of chlorine gas are reduced. Chlorine gas is an acute toxic gas that is hard to handle with regard to the working environment.
Results from the LCA show that disinfection with UV-light and monochloramin is about 45% more energy demanding than the other alternatives. The total use of energy with UV-disinfection is equal to 0.5-1% of the total energy required to produce and distribute the drinking water. Regarding to the environmental impacts the alternative with UV-disinfection contributes to the most amounts of greenhouse gases. The contribution of emissions that led to eutrofication and acidification dominates by the alternative with disinfection with hypochlorite.
To compare the human toxic risks two different methods has been used. According to the first method, USES-LCA, the biggest human toxic risks occurs with disinfection with hypochlorite and chlorine gas. With the other method, EDIP, the greatest risks occurs with disinfection with hypochlorite and disinfection with UV-light.
The positive effects of the changeover to UV-disinfection are received at the expense of higher energy consumption. Thich alternative to prefer are decided by how the values are made between the studied parts; energy- and environmental aspects verses health aspects and the working environment.