Annual photosynthetic response of phototrophic biofilms from an Italian wastewater treatment plant
Guzzon, Antonella; Albertano, Patrizia
The photosynthetic capacity of phototrophic biofilms growing on artificial substrata in the sedimentation (ST) and chlorination (CT) tanks of the wastewater treatment plant (WWTP) of Fiumicino Airport (Rome, Italy) was studied over an annual cycle. Photosynthesis versus Irradiance (P/I) curves and quantification of chlorophylls, total carotenoids and phycobiliproteins were carried out monthly on biofilms collected after one week incubation in the tanks to assess their light acclimation ability and their biomass variation over an annual period. The in situ ST and CT phototrophic communities acclimated to the seasonal changes of irradiance by varying the maximum rate of photosynthesis (Pmax) and photosynthetic efficiency (α). The highest Pmax and α occurred in winter, although phototrophic biomass (indicated by chlorophyll-a) peaked in spring. The development of the phototrophic community affected the light response as suggested by the significant positive correlation found between the photosynthetic parameters and Chl-a concentration. Chlorophyll ratios showed a higher spatial homogeneity of cyanobacteria and microalgae in ST than in CT. The total carotenoids/Chl-a ratio was fairly constant over the experimental period while higher phycobiliproteins (PBP)/Chl-a values were found in winter depending on cyanobacteria acclimation to lower irradiance. Data indicated that the phototrophic biofilms studied were able to maintain high rates of photosynthesis and biomass production at varying seasonal irradiance and, therefore, to be potentially useful as bioremediation tool in wastewater treatment.