The mechanism of microalgal adhesion to fungal pellets and its applications

Abstract: This work is concerned with the use of fungi to harvest microalgae. The ability of Aspergillus niger and Trichoderma harzianum to harvest cells of Chlorella vulgaris and Scenedesmus ssp. was assessed in several experiments designed to elucidate the adhesion mechanism. While A. niger was able to form co-pellets with both C. vulgaris and Scenedesmus ssp. by addition of spores to the algal culture, T. harzianum only produced filamentous mats. When KCl was added to the medium, the supernatant of the co-culture with A. niger and C. vulgaris was opaque compared to the clear supernatant of the co-culture without KCl. This implies that the adhesion of microalgal cells to the fungal hyphae is influenced by electrostatic interactions. Cells of C. vulgaris adhered to the surface of pre-made pellets of both fungal species but the pellets A. niger collected more cells than those of T. harzianum. The capability of fungi to harvest microalgae can be an important aspect of the transition to a biobased society as microalgae is seen as a promising renewable source of both oil and fermentables for the bioenergy industries.