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Título da Dissertação: Avaliação de filtros lentos de areia como pré-tratamento para o controle de biofouling em plantas de osmose reversa aplicadas na dessalinização de água do mar.

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The present work has evaluated the performance of seawater treatment by biological sand filters in order to control microbial biofilms formation in reverse osmosis membranes, used for the desalination process. The same filters were also evaluated as a seawater treatment system for aquaculture, and the performance in biofilms control inside the fish tanks was verified. To evaluate the performance in terms of biofilms control, proteins and carbohydrates (main components of biofilms) were quantified in specimens exposed to different treatments. The water produced by the treatments was also evaluated by microorganisms concentration and assimilable organic carbon content, which is associated with microbial growth potential. The performance of turbidity removal and SDI reduction from raw water was also an evaluation parameter. From the data obtained, it was observed that seawater treatment systems by of slow sand filters are able to reduce reverse osmosis membranes biofilms (up to 80% proteins concentration and 88% carbohydrate concentration). However, in order to have a significant rate of AOC removal and PCM reduction, these systems need a maturation time between 50 and 60 days. On the other hand, in terms of turbidity removal and SDI reduction, these systems demonstrate immediate efficiency, resulting in water turbidity always less than 0.3 UNT and SDI always less than 4. The slow sand filters showed efficience to reduce the biofilm formation and material deposition inside the fish tanks, this reduction was more evident at the bottom of the tanks and after 31 days. The use of sand filters as a water treatment for fish farming can contribute to reduce the number of procedures for handling and cleaning tanks.