The bio®lms were mainly made up of Beggiatoa ssp., and
Sphaerotilus natans, which is concordant with the observations
made by several authors [4±6, 10]. Also, Haliscomenobacter
hydrossis, Thiothrix ssp., type 021N, type
0803, type 0914, type 0961, type 1701, type 1851, and type
1863 were observed in a smaller proportion that the former
microorganisms.