School of Chemistry - Research Publications
Permanent URI for this collection
Search Results
1 - 4 of 4
-
ItemThe effect of high-intensity ultrasound on cell disruption and lipid extraction from high-solids viscous slurries of Nannochloropsis sp biomass(ELSEVIER SCIENCE BV, 2018-11-01)The effect of ultrasonication on the cell rupture of marine microalgae Nannochloropsis sp. was studied as a function of the slurry solids concentration and treatment time. The concentrated viscous wet-biomass (~12 to 25% solids concentration) was subjected to ultrasonication (20 kHz) at 3.8 W/mL for up to 5 min. Compared to extraction without cell rupture, sonication led to a significant increase in lipid yield from ~11% to about 70% within 5 min of sonication. The extraction yield was found to decrease with increased solids concentration, with a large decrease between 20% to 25% solids. This is attributed to the increase in viscosity and decrease in speed of sound with increase in solids. The ultrasound attenuation coefficient increased 320-fold as the solids increased from 20 to 25%. Such a large attenuation of ultrasound places a limit of 20% solids to be used for cell rupture by ultrasound. The specific energy requirements per unit mass of extracted lipid were lowest at 20% solids. At lower concentrations energy was wasted heating water, at higher concentrations the lipid yields were reduced due to ultrasound attenuation.
-
ItemUltrasonic pretreatment of food waste to accelerate enzymatic hydrolysis for glucose production(ELSEVIER SCIENCE BV, 2019-05-01)Recovering valuable materials from food waste by applying the concept of a bio-refinery is attracting considerable interest. To this effect, we investigated the possibility of enhancing the enzymatic hydrolysis of food waste using ultrasonic technology. The effect of pre-treating blended food waste with high-intensity ultrasound (20 kHz) on subsequent hydrolysis by glucoamylase was investigated as a function of sonication time and temperature. Particle sizing by laser diffraction, and imaging via scanning electronic microscopy showed that ultrasonic pre-treatment could reduce the particle size of the blended food waste significantly, resulting in a better interaction with the enzyme. As a consequence, the glucose yield of enzymatic hydrolysis was ∼10% higher for food waste pre-sonicated using the most intensive ultrasonication conditions studied (5 min sonication at a power of 0.8 W/mL at 20 °C) than for the untreated control. In addition, the time required to achieve high yields of glucose could be more than halved using ultrasonic pre-treatment. This could enable the hydrolysis reactor size or the enzyme usage to be reduced by more than 50%. Therefore, an ultrasound-assisted bioconversion process from food waste into a value-added product has been demonstrated.
-
ItemEmulsifying properties of ruptured microalgae cells: Barriers to lipid extraction or promising biosurfactants?(ELSEVIER SCIENCE BV, 2018-10-01)A systematic investigation of the emulsifying properties of ruptured algae cells was performed for the first time. The slurry of ruptured algae cells was separated into different biomass fractions, namely the cell debris, the delipidated debris, the serum, and the lipid. The interfacial interactions of these biomass fractions with a nonpolar solvent (e.g. hexane or hexadecane) were characterized using pendant drop tensiometry and interfacial shear rheology. The stability of the different emulsions (formed by the different biomass fractions) was tested using analytical centrifugation. The extracted lipid was an excellent surfactant that reduced the interfacial tension, however, it was not effective at stabilizing the emulsions. The protein-rich serum produced a strong interfacial film that stabilized the emulsions against coalescence during centrifugation. The cell debris stabilized the emulsions to a lesser extent by adsorbing to the droplet surface, presumably via interactions with hydrophobic extracellular polymeric substances (EPS). However, neither the serum nor the cell debris were very effective surfactants, and required the presence of the lipid fraction to produce small emulsion droplets. When present together, the components exhibited competitive interfacial adsorption, which influenced emulsion stability. In particular, the interruption of the protein film by the presence of lipid or cell debris reduced the stability of the emulsions. This study provides a new mechanistic understanding of emulsification during wet lipid extraction from microalgae that will be useful for determining strategies to improve solvent recovery. The results also suggest potential for developing effective bioemulsifiers or biosurfactants from fractionated microalgae biomass for commercial application.
-
ItemRheological properties of concentrated slurries of harvested, incubated and ruptured Nannochloropsis sp. cells(Springer Science and Business Media LLC, 2019-12)Biorefining of microalgae biomass requires processing of high-solids (> 10%) slurries. To date there is little knowledge of how processes for weakening and rupturing microalgae cells affect the rheological properties of these materials. To fill this gap in the literature, the rheological properties of concentrated slurries of marine microalgae Nannochloropsis sp. were investigated as a function of processing and solids concentration (12, 20 and 24% w/w). Freshly harvested, incubated (autolysed), and high-pressure homogenised (HPH) slurries were found to be shear thinning up to a shear rate of approximately 200 s− 1. Viscosity increases were far more prominent for partially processed versus unprocessed algal pastes at the higher concentrations. Slurry viscosity as a function of cell volume fraction could not be fitted to the Krieger-Dougherty model due to a network structure resulting from extracellular polymeric substances (EPS) and the intracellular cell components released during incubation and cell rupture. The 24% slurry, which was near the close packing limit, was much more viscous than the less concentrated slurries when comprising whole cells (i.e. harvested and incubated slurries). Cell rupture by HPH completely altered the characteristics of the slurry, increasing the viscosity of even the less concentrated slurries, and producing irreversible shear thinning behaviour. The magnitude of the increases in viscosities and the irreversible shear thinning behaviour observed in this study, have significant implications for processing and optimising the solids concentration of algal slurries.