LCA tool for the environmental evaluation of potable water production

Environmental impact assessment will soon become a compulsory phase in future potable water production projects, especially when alternative treatment processes such as desalination are considered. An impact assessment tool is therefore developed for the environmental evaluation of potable water production. The evaluation method used is the life cycle assessment (LCA) method. The quick and easy assessment of energetic and environmental performances contributes to determine the weak points of potable water production processes or the best suited treatment in a specific context. Studies of some potable water supply scenarios (groundwater treatment, ultrafiltration, nanofiltration, seawater reverse osmosis and thermal distillation associated to water transfer) are presented in order to illustrate the environmental information drawn from this tool. The main source of impacts is shown to be electricity production for plant operation. Improvement levers are presented for impact reduction and for the objective comparison between alternative and conventional water treatment processes.

In response to stakeholders needs, a LCA tool has been developed for the environmental evaluation of potable water supply scenarios with various project conditions. This is made possible by modeling each unitary water treatment step as a function of the local context. Different water treatment processes, plants and potable water supply systems are then analyzed in order to present the main results. At the scale of the water treatment process, energy consumption is shown to carry the highest environmental burden of potable water production. Chemicals production for coagulation and remineralization represent the second major contribution to impacts. The treatment processes dedicated to alternative water resources (advanced membrane processes and desalination) have higher chemicals and energy consumption than conventional groundwater and surface water treatment processes. In the current LCA framework, these alternative treatment processes therefore generate higher impacts than conventional treatment processes based on freshwater resources. Development levers for impact reduction are presented such as the installation of high efficiency pumping systems, the optimization of membrane process designs or the use of alternative chemicals. At the scale of the potable water production plant, energy consumption contributes to the majority of plant impacts due to the high electricity consumption of intake pumping and potable water distribution. Hence the life cycle electricity consumption is introduced as a meaningful indicator of the plant environmental performance. In this respect, plant impacts depend highly on the electricity supply. They could be mitigated by contracting a certified high quality electricity supply (green electricity from renewable sources for example). For a given water stress situation, potable water supply alternatives based on different water resources are compared. The impact of water transfer is evaluated. It allows to identify the areas for which distant conventional treatments requiring water transfer will generate potentially more impacts than local alternative treatments.