Water treatments in semi-closed cooling circuits and their impact on the quality of effluents discharged by CERN

The main goal of this study is to assess the impact of the discharges of the semi-closed water cooling circuits of CERN (European Center for Nuclear Research) on the overall quality of CERN's effluents, taking as guidelines the international legislation supported on the knowledge of the water systems of CERN. In order to reach this goal, a thorough analysis of the functioning of the semi-closed water cooling systems of CERN's particle accelerators was done, as well as, an analysis of the treatment that is done to prevent the proliferation of bacteria such as Legionella. The products used in these water treatments, as well as their impact, were also researched. In addition, a study of the applicable regulation to CERN's effluent was done. This study considered not only the regulation of France and Switzerland (CERN's host states) but also the international regulation from the European community, Portugal Germany, Spain, U.S. and Canada, having in view a better understanding of the limit values of the parameters of the CERN's host states, as well as, the possibility of setting a CERN's internal regulation concerning water discharges. Considering the applicable regulation, the products used and the discharge conditions of the water systems, a research on the types of parameters to analyse was undertaken, bearing in mind the controversy on parameters such as AOX. This research was the foundation for conducting four water sampling campaigns: two of which during preventive shock treatment and the remaining two during regular treatment. The objective of the first two campaigns was broader and intended to check the conformity of CERN's effluents with the regulations of the host states; On the other hand, the sampling campaigns conducted during regular treatment were oriented to deepen the knowledge on problematical parameters such as AOX, COD, DOC, Chlorine and Zinc. The preparation for these campaigns included also the choice of other aspects such as: the three sampling points (RAMSES, SF1 and building 863), the definition of the schedule for sampling and the selection of an external laboratory to conduct the analyses. The results of the analyses of CERN's effluents, at the discharge point (RAMSES), were fully compliant with the regulation. However, at the source of this effluents (circuits SF1 and building 863) non-conformities have surged. The parameters AOX, DOC, COD, Chlorine, Brome, Suspended matter, Zinc and Aluminium demonstrated to be the most problematic. To conclude this work, a search for alternative methods to conventional water quality parameters was done that included a study on the applicability of ecotoxicological tests. As a result of this study, a final sampling campaign was performed using the tests Microtox (Vibrio fischeri), Green Algae (Pseudokirchneriella subcapitata), Micro- crustaceans (Da phnia magna), Macrophytes (Lemma minor) having obtained results that were conducive with the previous results. This way, RAMSES didn't not show any toxicity on the four tests whilst SF1 evidenced toxicity, being most sensitive to the Micro-crustaceans test where it presented a UT50 value of 7,1 and EC50 value of 14,2 %.