Ultrasonic disintegration of microalgal biomass and consequent improvement of bioaccessibility/bioavailability in microbial fermentation

Abstract

BackgroundMicroalgal biomass contains a high level of carbohydrates which can be biochemically converted to biofuels using state-of-the-art strategies that are almost always needed to employ a robust pretreatment on the biomass for enhanced energy production. In this study, we used an ultrasonic pretreatment to convert microalgal biomass (Scenedesmus obliquus YSW15) into feasible feedstock for microbial fermentation to produce ethanol and hydrogen. The effect of sonication condition was quantitatively evaluated with emphases on the characterization of carbohydrate components in microalgal suspension and on subsequent production of fermentative bioenergy.MethodScenedesmus obliquus YSW15 was isolated from the effluent of a municipal wastewater treatment plant. The sonication durations of 0, 10, 15, and 60 min were examined under different temperatures at a fixed frequency and acoustic power resulted in morphologically different states of microalgal biomass lysis. Fermentation was performed to evaluate the bioenergy production from the non-sonicated and sonicated algal biomasses after pretreatment stage under both mesophilic (35°C) and thermophilic (55°C) conditions.ResultsA 15 min sonication treatment significantly increased the concentration of dissolved carbohydrates (0.12 g g-1), which resulted in an increase of hydrogen/ethanol production through microbial fermentation. The bioconvertibility of microalgal biomass sonicated for 15 min or longer was comparable to starch as a control, indicating a high feasibility of using microalgae for fermentative bioenergy production. Increasing the sonication duration resulted in increases in both algal surface hydrophilicity and electrostatic repulsion among algal debris dispersed in aqueous solution. Scanning electron microscope images supported that ruptured algal cell allowed fermentative bacteria to access the inner space of the cell, evidencing an enhanced bioaccessibility. Sonication for 15 min was the best for fermentative bioenergy (hydrogen/ethanol) production from microalga, and the productivity was relatively higher for thermophilic (55°C) than mesophilic (35°C) condition.ConclusionThese results demonstrate that more bioavailable carbohydrate components are produced through the ultrasonic degradation of microalgal biomass, and thus the process can provide a high quality source for fermentative bioenergy production.

Microalgal biomass pretreatment for bioethanol production: a review

“…This type of technology can help break the cell wall of microalgae because when bubbles collapse on the surface of a solid, the pressure and elevated temperature create microjets that allow the solvent to penetrate into the raw material and a rupture of the cell wall occurs (Luo et al, 2014). In a previous work reported by Jeon et al (2013), Scenedesmus obliquus biomass was submitted to ultrasound treatment between 10 -60 min to facilitate the accessibility of bacteria to ferment the sugars present intracellularly in the biomass, with best pretreatment found within a time The use of ultrasound also offers the opportunity to modify and improve some important features of bioactive compounds without removing their biological properties (Jambrak et al, 2010). For instance, in third generation bioethanol production, the starch present in microalgae can be modified leading to improvements in the subsequent enzymatic hydrolysis.…”

Bacterial cellulose production by Komagataeibacter hansenii using algae-based glucose

“…Cells were double-washed with sterile ultrapure water and dried in an oven at 80°C to a constant weight to determine the dry weight of algal cells. Sonication was performed on dried algal cells in order to destroy cell wall to release starch packages, at 45°C, in sterile ultrapure water, for 15 min, as described by Jeon et al (2013), and algal lysate was freeze-dried for further steps.…”

Utilization of Microalgal Biofractions for Bioethanol, Higher Alcohols, and Biodiesel Production: A Review

“…Ultrasonication is a developing technology with the potential to decrease chemical loading and reaction time. It effectively modifies the surface structure of biomass which lead to enhanced saccharification [45,51]. It has been widely used for homogenization and disruption of the rigid cell wall of microalgae.…”