Hydrothermal microwave processing of microalgae as a pre-treatment and extraction technique for bio-fuels and bio-products

Abstract

Microalgae are regarded as a promising source of lipids for bio-diesel production and bioproducts. The current paper investigates the processing of microalgal slurries under controlled microwave irradiation. Microwave power was applied to reach temperatures of 80, 100, 120 and 140°C at a constant residence time of 12 min. Microwave irradiation led to disruption of the algal cell walls which facilitated lipid extraction. The influence of inorganic material on microwave heating was assessed for three strains including, Nannochloropsis occulata, Chlorogloeopsis fritschii and Pseudochoricystis ellipsoidea. Mass balances were calculated and showed that the amount of carbon, nitrogen and total mass recovered in the residue was highly dependent on process conditions and algae strain. Hydrothermal microwave processing (HMP) was found to be an effective pre-treatment for hydrothermal liquefaction and extraction of lipids and phytochemicals.

Two-stage hydrothermal liquefaction of a high-protein microalga

“…This has raised the question as to whether it is possible to extract nitrogen-containing components prior to high-temperature HTL (which is carried out typically at temperatures in the range of 300 to 350°C). In particular, reductions in nitrogen contents of the final bio-crude product are achieved through an initial mild HTL (temperatures b 200°C) as a preliminary treatment, albeit with concomitant reduction in the quantity of the bio-crude generated [12][13][14][15]. While these results are promising, the relationships between quality and quantity of the bio-crude produced in such two-stage treatments are poorly understood.…”

Investigation of the effects of microalgal cell concentration and electroporation, microwave and ultrasonication on lipid extraction efficiency

“…Several studies [7e12] employed the Bligh and Dyer method [13], which uses chloroform, methanol, and water as co-solvents for extracting and purifying lipids. Additionally, other solvent systems have been investigated as possible extracting solvents, including dichloromethane/methanol/water [14], dichloromethane/water [15], nhexane/water [12], and ethanol/water and hexane/water [16].…”

“…Several pretreatment methods have been investigated to improve the efficiency of solvent extraction systems, including ultrasonication [7e12, 14,17], microwave [7e11, 14,15], electroporation [18], and bead mills, autoclave and osmotic pressure [7]. These studies reported a significant increase in the quantity of lipids extracted due to pretreatment.…”

“…For ultrasonication, the percent increase ranged from 30% [10] to 400% [8] with a mean and median of 136% and 99%, respectively. The percent increase for microwaves ranged from 38% [14] to 606% [15] with a mean and median of 288% and 150%, respectively. However, a majority of these studies included additional sample processing steps before pretreatment and extraction, including freeze drying [8e11, 14,15] and treating the sample with saline solution [17], making very difficult the quantification of the effects of the pretreatments on lipids extraction.…”

Green microalgae biomolecule separations and recovery

“…Heat in the cell suspension results from rotation and vibration of dipolar molecules and ions in an electromagnetic field (Biller et al 2013). Advantages include short residence/processing time, scalability, high efficiency, low energy consumption, and low risk of metabolite denaturation (Günerken et al 2015;Biller et al 2013;Pasquet et al 2011).…”