Microalgal biofilms for nutrient removal from industrial wastewater
The aim of this Ph.D. research was to develop a bench scale microalgae biofilm technology for phosphorus rich effluents toward the production of secondary valuable products, i.e. phosphorus recovery. Fundamental research was conducted to select efficient microalgae strains in terms of successful wastewater treatment and algal biomass production in order to develop a process with low addition of electricity and chemical reagents. A total of 24 microalgae strains were screened and seven strains were selected according to their growth rate. The growth rate and nutrient removal efficiency of six strains were evaluated under different synthetic wastewater conditions, Chlorella vulgaris ACUF_809 showed superior efficiency of phosphate removal compared with the strains screened. Chlorella sp. ACUF_802 was characterized additionally by the effect of nitrogen and phosphorus limiting conditions in the growth medium. Laboratory scale experiments were done to evaluate the biofilm formation performance on textile fabrics, photosynthetic activity, colonization percentage and biomass growth for two isolated Chlorella spp. differences in biofilm formation performance were observed between the strains. It was found that combined analysis of non-destructive optical methods is an effective methodology for monitoring the early stages of biofilm development. Biofilm average thickness (106.37 ± 47 µm) was measured. Furthermore, as a promising valuable recovery product, phosphate distribution and localization during C. pyrenoidosa ACUF_808 and C. vulgaris ACUF_809 biofilms development were examined over time and keeping the spatial context unaltered. Using physiological measurements combined with advanced microscopic, spectroscopic and mass spectrometric techniques, cellular growth, cell adhesion, physiological performance and nutrient (phosphate and nitrate) removal were determined. Moreover, phosphate accumulation at single-cell level within the biofilms was visualized.
The nutrient removal efficiency by the microalgae Scenedesmus vacuolatus ACUF_053 and C. vulgaris ACUF_809 from synthetic wastewater in a new laboratory configuration biofilm photobioreactor (PBR) was studied. Biofilm development on cotton fabric was followed in the PBR under semi-batch conditions during 41 days. Complete nutrient removal was obtained by S. vacuolatus ACUF_053 and five stages in the development of the biofilms were identified: 1) attachment, 2) biofilm formation, 3) maturation I, 4) selection/adaptation and 5) maturation II. In contrast, C. vulgaris ACUF_809 biofilm development showed a more regular biomass growth and constant removal efficiency. This research offers novel fundamental information in the field of microalgae biofilm formation with a scope for a wider range of scientific applications, including the possibility of coupled wastewater treatment with potential recovery of phosphate.