This experimental study reports the adhesion rate and adhesion density of Chlorella vulgaris on hydrophilic glass, and hydrophobic indium tin oxide (ITO) surfaces at constant shear rate. Cultivation of algae as biofilms offers an energy and water efficient method for algal biofuel production. In order to design algal biofilm cultivation systems, algal adhesion and biofilm formation on substrates with different surface properties must be known. To assess this, a parallel plate flow chamber was used to quantify the adhesion rate of the commonly used algae Chlorella vulgaris to the surfaces under controlled shear rates. The contact angle and zeta potential measurements were made both for the algal cells and the adhesion surfaces to model adhesion. The experimental results were compared with the predictions of the Derjaguin, Landau, Verwey, Overbeek (DLVO), extended DLVO (XDLVO) theories, and the thermodynamic model. The experiments showed that the rate of adhesion over the hydrophobic surface was 81 cells mm−2min−1 which was 3 times larger than that of the hydrophilic surface for the first forty minutes of the adhesion experiments. Moreover, the final adhesion density over the hydrophobic surface was 6182 mm−2 after an experimental duration of 320 minutes which was 2.7 times that of the hydrophilic surface. Detachment studies done with increased shear rates showed that the adhesion strength of algae was also higher over the hydrophobic surface. The experimental results fit best with the results from the XDLVO theory. However, the model was inaccurate in predicting high detachment rate from the hydrophilic surface with increased shear rates. Results show the importance of surface material selection for the initial adhesion of cells. These results can be used for selection and design of surface materials for optimizing initial adhesion of algae cells in algal biofilm photobioreactors. Furthermore, the results can also be used for the design of planktonic photobioreactors to avoid biofouling.

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