Phototrophic biofilms develop on every submerged surface of secondary treatment tanks of the Fiumicino Airoport (Rome, Italy) wastewater treatment plant (WWTP). Microalgae and cyanobacteria are commonly associated with heterotrophic microorganisms and enmeshed in a “glue-like” exopolymeric matrix. In order to better understand bioremediation potential of autochthonous biofilms, we focus on diversity (structure) and function of these surface-associated communities. We apply a range of microscopic techniques for composition and productivity of phototrophs and for the study of biofilm development on artificial substrata using CLSM and FISH. Matrix exopolysaccharides play an important role in adhesion processes and flux of substances, we analyse their monosaccharidic composition by RP-HPLC and the physico-chemical characteristics by means of circular dichroism. Specific objectives cover the assessment of N and P retention capacity of biofilms as their photosynthetic performance via the recording of P/I (Photosynthetic versus Irradiance) curves. Application of these results is foreseen in the field of algal biomass production, nutrients removal from effluent waters and bio-medical use of cyanobacterial exopolysaccharides.