Immobilization of Diatom Phaeodactylum tricornutum with Filamentous Fungi and Its Kinetics

Abstract

Immobilizing microalgae cells in a hyphal matrix can simplify harvest while producing novel mycoalgae products with potential food, feed, biomaterial, and renewable energy applications; however, limited quantitative information to describe the process and its applicability under various conditions leads to difficulties in comparing across studies and scaling-up. Here, we demonstrate the immobilization of both active and heat-deactivated marine diatom Phaeodactylum tricornutum (UTEX 466) using different loadings of fungal pellets (Aspergillus sp.) and model the process through kinetics and equilibrium models. Active P. tricornutum cells were not required for the fungal-assisted immobilization process and the fungal isolate was able to immobilize more than its original mass of microalgae. The Freundlich isotherm model adequately described the equilibrium immobilization characteristics and indicated increased normalized algae immobilization (g algae removed/g fungi loaded) under low fungal pellet loadings. The kinetics of algae immobilization by the fungal pellets were found to be adequately modeled using both a pseudo-second order model and a model previously developed for fungal-assisted algae immobilization. These results provide new insights into the behavior and potential applications of fungal-assisted algae immobilization.

Keywords: Aspergillus sp.; Freundlich isotherm; Microalgae immobilization; Phaeodactylum tricornutum; fungi; heat-deactivation.

Fig. 1. Fungal-assisted immobilization of active and heat-deactivated P. tricornutum microalgae by Aspergillus sp. UCD F01 fungal pellets. Data are presented as average ± standard deviation (n = 2).

Fig. 2

(A) Beginning of the immobilization process with a flask of heat-deactivated P. tricornutum and the addition of Aspergillus sp. UCD F01 fungal pellets (dark spheres); (B) the end of the immobilization process, subset arrows show filamentous hair-like structures; (C) a cross section of a fungal-algal pellet postimmobilization; post-immobilization pellets at a loading of (D) 0.73 g fungi/g algae and (E) 2.9 g/g; and (F) microscopic image (100× magnification) of the mat isolated from the surface of the pellet post-immobilization (sample stained with safranin to aid in contrast).

Fig. 3. Immobilization efficiency based on percentage removal of heat-deactivated microalgae P. tricornutum from solution at different initial loadings of Aspergillus sp. UCD F01 fungal pellets.

Fig. 4. The Freundlich isotherm and Bhattacharya models applied to the immobilization of P. tricornutum by Aspergillus sp. UCD F01.

Fig. 5

(A) Heat-deactivated P. tricornutum microalgae concentrations over time in response to different initial fungal (Aspergillus sp. UCD F01) pellet loadings along with the modeled fit to the pseudo-second order kinetic model, (B) the pH profile of the various fungal loadings in the experiment, (C) the plot used to determine the k constant in the pseudo-second order kinetic model, and (D) the Immobilization Index of the microalgae cultures over time and fit with the Bhattacharya kinetic model. Data are presented as average ± standard deviation (n = 2).