Large amounts of oily sludges are retained in patrol stations by gravity interceptors in order to prevent
their discharge in surface waters. Those residues are mainly composed of a mixture of hydrocarbons,
water and inert solids. Therefore, their final disposal represents a significant environmental problem. This
work concerns the study of microfauna biomass during the start-up of a SBBR designed for the treatment
of hydrocarbon slurries retained in an API oil separator. The findings of this study suggest that protozoal
colonization of the SBBR followed the same pattern of activated sludge systems, the free swimming and
crawling ciliates, and also fagellates being the dominant protozoa group during the star-up period of the
reactor. When the plant performance dropped, the number of flagellated protozoa rapidly increased, and a
concomitant decrease in the ciliated population was observed.Fundação para a Ciência e a Tecnologia (FCT)
