• Energy Research
• ES close
• CA close
• AU close

Microalgae have tremendous potential for producing liquid renewable fuel. Many methods for converting microalgae to biofuel have been proposed; however, an economical and energetically feasible route for algal fuel production is yet to be found. This paper presents a review on the comparison of the most promising conversion pathways of microalgae to liquid fuel: hydrothermal liquefaction (HTL), wet extraction and non-destructive extraction. The comparison is based on important assessment parameters of product quality and yield, nutrient recovery, GHG emissions, energy and the cost associated with the production of fuel from microalgae, in order to better understand the pros and cons of each method. It was found that the HTL pathway produces more oil than the wet extraction pathway; however, higher concentrations of unwanted components are present in the HTL oil produced. Less nutrients (N and P) can be recovered in HTL compared to wet extraction. HTL consumes more fossil energy and generates higher GHG emissions than wet extraction, while the production cost of fuel from HTL pathway is lower than wet extraction pathway. There is considerable uncertainty in the comparison of the energy consumption and economics of the HTL pathway and the wet extraction pathway due to different scenarios analysed in the assessment studies. To be able to appropriately compare methodologies, the conversion methods should be analysed from growth to upgradation of oil utilising sufficiently similar assumptions and scenarios. Based on the data in available literature, wet oil extraction is the more appropriate system for biofuel production than HTL. However, the potential of alternative extraction/conversion technologies, such as, non-destructive extraction, need to be further assessed.

Microalgae have tremendous potential for producing liquid renewable fuel. Many methods for converting microalgae to biofuel have been proposed; however, an economical and energetically feasible route for algal fuel production is yet to be found. This paper presents a review on the comparison of the most promising conversion pathways of microalgae to liquid fuel: hydrothermal liquefaction (HTL), wet extraction and non-destructive extraction. The comparison is based on important assessment parameters of product quality and yield, nutrient recovery, GHG emissions, energy and the cost associated with the production of fuel from microalgae, in order to better understand the pros and cons of each method. It was found that the HTL pathway produces more oil than the wet extraction pathway; however, higher concentrations of unwanted components are present in the HTL oil produced. Less nutrients (N and P) can be recovered in HTL compared to wet extraction. HTL consumes more fossil energy and generates higher GHG emissions than wet extraction, while the production cost of fuel from HTL pathway is lower than wet extraction pathway. There is considerable uncertainty in the comparison of the energy consumption and economics of the HTL pathway and the wet extraction pathway due to different scenarios analysed in the assessment studies. To be able to appropriately compare methodologies, the conversion methods should be analysed from growth to upgradation of oil utilising sufficiently similar assumptions and scenarios. Based on the data in available literature, wet oil extraction is the more appropriate system for biofuel production than HTL. However, the potential of alternative extraction/conversion technologies, such as, non-destructive extraction, need to be further assessed.

Sustainable electricity generation is one of the major current challenges for our society. In this context, the evolution of nanomaterials and nanotechnologies has enabled the fabrication of microscopic devices to produce clean energy from a great variety of renewable sources. To expand the possibilities of energy generation, we have designed and fabricated bioinorganic generators capable to produce electricity by conversion of chemical energy from renewable fuel sources. Unlike traditional generators, the systems described herein produce mechanical energy through enzyme-driven gas production which generates vibration and pressure that are thus converted into electricity by the action of a piezoelectric component properly integrated into the device. Our generators are able to produce an electric ernergy from different renewable sources like glucose, ethanol, and amino acids, attaining energy outputs around 250 nJ cm–2 and reaching maximum open-circuit voltages of up to 1 V. In addition, the produced energy can be easily regulated by adjusting both enzyme and fuel concentration which can tune the electrical output according to the application. The systems described herein propose a new concept for self-sufficient energy harvesting that bridges biocatalysis and piezoelectricity, where the energy production is based on the piezoelectric effect triggered by enzymatic action rather than on the enzyme-driven electron transfer that governs biofuel cells. Although the electric output is too low yet to be considered an alternative for energy production, this technology opens the door to power small devices. We envision the utilization of this technology in such remote locations where mechanical energy is lacking but there are chemical energy reservoirs. We would like to acknowledge Marie-Curie Actions (NANOBIENER project), IKERBASQUE foundation for funding F.L.-G., and the support of COST Action CM1303 Systems Biocatalysis. We also acknowledge HERGAR foundation for the funding. Peer reviewed

Sustainable electricity generation is one of the major current challenges for our society. In this context, the evolution of nanomaterials and nanotechnologies has enabled the fabrication of microscopic devices to produce clean energy from a great variety of renewable sources. To expand the possibilities of energy generation, we have designed and fabricated bioinorganic generators capable to produce electricity by conversion of chemical energy from renewable fuel sources. Unlike traditional generators, the systems described herein produce mechanical energy through enzyme-driven gas production which generates vibration and pressure that are thus converted into electricity by the action of a piezoelectric component properly integrated into the device. Our generators are able to produce an electric ernergy from different renewable sources like glucose, ethanol, and amino acids, attaining energy outputs around 250 nJ cm–2 and reaching maximum open-circuit voltages of up to 1 V. In addition, the produced energy can be easily regulated by adjusting both enzyme and fuel concentration which can tune the electrical output according to the application. The systems described herein propose a new concept for self-sufficient energy harvesting that bridges biocatalysis and piezoelectricity, where the energy production is based on the piezoelectric effect triggered by enzymatic action rather than on the enzyme-driven electron transfer that governs biofuel cells. Although the electric output is too low yet to be considered an alternative for energy production, this technology opens the door to power small devices. We envision the utilization of this technology in such remote locations where mechanical energy is lacking but there are chemical energy reservoirs. We would like to acknowledge Marie-Curie Actions (NANOBIENER project), IKERBASQUE foundation for funding F.L.-G., and the support of COST Action CM1303 Systems Biocatalysis. We also acknowledge HERGAR foundation for the funding. Peer reviewed

New transparent optodes for life-time based microscopic imaging of O₂ were developed by spin-coating a μm-thin layer of a highly luminescent cyclometalated iridium(III) coumarin complex in polystyrene onto glass cover slips. Compared to similar thin-film O₂ optodes based on a ruthenium(II) polypyridyl complex or a platinum(II) porphyrin, the new planar sensors have i) higher brightness allowing for much shorter exposure times and thus higher time resolution, ii) more homogeneous and smaller pixel to pixel variation over the sensor area resulting in less noisy O₂ images, and iii) a lower temperature dependency simplifying calibration procedures. We used the new optodes for microscopic imaging of the spatio-temporal O₂ dynamics at the base of heterotrophic biofilms in combination with confocal imaging of bacterial biomass and biofilm structure. This allowed us to directly link biomass distribution to O₂ distribution under both steady state and non-steady state conditions. We demonstrate that the O₂ dynamics in biofilms is governed by a complex interaction between biomass distribution, mass transfer and flow that cannot be directly inferred from structural information on biomass distribution alone.

New transparent optodes for life-time based microscopic imaging of O₂ were developed by spin-coating a μm-thin layer of a highly luminescent cyclometalated iridium(III) coumarin complex in polystyrene onto glass cover slips. Compared to similar thin-film O₂ optodes based on a ruthenium(II) polypyridyl complex or a platinum(II) porphyrin, the new planar sensors have i) higher brightness allowing for much shorter exposure times and thus higher time resolution, ii) more homogeneous and smaller pixel to pixel variation over the sensor area resulting in less noisy O₂ images, and iii) a lower temperature dependency simplifying calibration procedures. We used the new optodes for microscopic imaging of the spatio-temporal O₂ dynamics at the base of heterotrophic biofilms in combination with confocal imaging of bacterial biomass and biofilm structure. This allowed us to directly link biomass distribution to O₂ distribution under both steady state and non-steady state conditions. We demonstrate that the O₂ dynamics in biofilms is governed by a complex interaction between biomass distribution, mass transfer and flow that cannot be directly inferred from structural information on biomass distribution alone.

Abstract Fractures along interfaces between host rock and wellbore cement have long been identified as potential CO2 leakage pathways from subsurface CO2 storage sites. As a consequence, cement alteration due to exposure to CO2 has been studied extensively to assess wellbore integrity. Previous studies have focused on the changes to either chemical or mechanical properties of cement upon exposure to CO2-enriched brine, but not on the effects of loading conditions. This paper aims to correct this deficit by considering the combined effects of the fracture pathway and changing effective stress on chemical and mechanical degradation at conditions relevant to geologic carbon storage. Flow-through experiments on fractured cores composed of cement and tight sandstone caprock halves were conducted to study the alteration of cement due to exposure to CO2-enriched brine at 3, 7, 9, and 12 MPa effective stress. We characterized relevant reactions via solution chemistry; fracture permeability via changes to differential pressure; mechanical changes via micro-hardness testing, and pore structure changes via x-ray tomography. This study showed that the nature and the rates of the chemical reactions between cement and CO2 were not affected by the effective stress. The differences in the permeability responses of the fractures were attributed to interactions among the geometry of the flow path, the porosity increase of the reacted cement, and the mechanical deformation of reacted asperities. The suite of observed chemical reactions contributed to change in cement mechanical properties. Compared to the unreacted cement, the average hardness of the amorphous silica and depleted layers was decreased while the hardness of the calcite layer was increased. Tomographic imaging showed that preferential flow paths formed in some of the core-flood experiments, which had a significant impact on the permeability response of the fractured samples. We interpreted the observed permeability responses in terms of competition between dissolution of cement phases (leading to enhanced permeability) and mechanical deformation of reacted regions (leading to reduced permeability).

Abstract Fractures along interfaces between host rock and wellbore cement have long been identified as potential CO2 leakage pathways from subsurface CO2 storage sites. As a consequence, cement alteration due to exposure to CO2 has been studied extensively to assess wellbore integrity. Previous studies have focused on the changes to either chemical or mechanical properties of cement upon exposure to CO2-enriched brine, but not on the effects of loading conditions. This paper aims to correct this deficit by considering the combined effects of the fracture pathway and changing effective stress on chemical and mechanical degradation at conditions relevant to geologic carbon storage. Flow-through experiments on fractured cores composed of cement and tight sandstone caprock halves were conducted to study the alteration of cement due to exposure to CO2-enriched brine at 3, 7, 9, and 12 MPa effective stress. We characterized relevant reactions via solution chemistry; fracture permeability via changes to differential pressure; mechanical changes via micro-hardness testing, and pore structure changes via x-ray tomography. This study showed that the nature and the rates of the chemical reactions between cement and CO2 were not affected by the effective stress. The differences in the permeability responses of the fractures were attributed to interactions among the geometry of the flow path, the porosity increase of the reacted cement, and the mechanical deformation of reacted asperities. The suite of observed chemical reactions contributed to change in cement mechanical properties. Compared to the unreacted cement, the average hardness of the amorphous silica and depleted layers was decreased while the hardness of the calcite layer was increased. Tomographic imaging showed that preferential flow paths formed in some of the core-flood experiments, which had a significant impact on the permeability response of the fractured samples. We interpreted the observed permeability responses in terms of competition between dissolution of cement phases (leading to enhanced permeability) and mechanical deformation of reacted regions (leading to reduced permeability).