Franziska Bleeke

• Even though microalgae show great potential for biomass production, industrial application has been limited in the past due to high production costs. Two major bottlenecks affecting cost effectiveness are the choice of a suitable production strain and the biomass harvest. Three manuscripts were published in the framework of the PhD Thesis, scientifically investigating new methods for strain selection and biomass harvest. In “Isolation and Characterization of New Temperature Tolerant Microalgal Strains for Biomass Production”, 130 environmental samples were taken in Germany, Spain, Italy and Portugal, purified and strains with a high growth rate and thermos tolerance were identified. 21 of the isolated strains were able to grow at 40 °C with the highest growth rate of 1.16 per day and 13 of those were even growing at 45 °C with a maximum growth rate of 0.053 per day at 45 °C. Sequencing showed that the isolates were all chlorophytes belonging to four different families. “Optimization of freshwater microalgal biomass harvest using polymeric flocculants” investigates 15 polyelectrolytes for their harvesting capability. Cationic, anionic and non-ionic flocculants were analyzed at varying concentrations and incubation times. Three chlorophytes were tested to verify the influence of different sizes, morphologies and motilities. In a recycling experiment the impact of flocculant residues was monitored over eight weeks. Cationic flocculants were most effective with flocculant PK55H showing the highest efficiency at the lowest concentration. Anionic and non-ionic flocculants were ineffective. “Effect of voltage and electrode material on electroflocculation of Scenedesmus acuminatus” tested six electrode materials for electroflocculation. Besides aluminum and iron electrodes, magnesium, copper, zinc and brass electrodes were tested and compared. The influence of 10, 20, 30 and 40 V was examined and evaluated. Maximum flocculation efficiency was reached with magnesium.