Biofuel production potentials in Europe: Sustainable use of cultivated land and pastures. Part I: Land productivity potentials

IIASA's agro-ecological zones modelling framework has been extended for biofuel productivity assessments distinguishing five main groups of feedstocks covering a wide range of agronomic conditions and energy production pathways, namely: woody lignocellulosic plants, herbaceous lignocellulosic plants, oil crops, starch crops and sugar crops. A uniform Pan-European land resources database was compiled at the spatial resolution of 1 km². Suitability and productivity assessments were carried out by matching climate characteristics with plant requirements, calculating annual biomass increments or yields including consideration of soil and terrain characteristics of each grid-cell.Potential biomass productivity and associated energy yields were calculated for each grid-cell. Spatial distributions of suitabilities of biofuel feedstocks in Europe were generated for each individual feedstock as well as for the five biofuel feedstock groups. Estimated agronomical attainable yields, both in terms of biomass (kg ha^?1) as well as biofuel energy equivalent (GJ ha^?1), were mapped and tabulated by agriculture and pasture land cover classes as derived from the CORINE land cover database. Results have been further aggregated by administrative units at NUTS 2 level.     

Synergistic carbon metabolism in a fast growing mixotrophic freshwater microalgal species Micractinium inermum

In recent years microalgae have attracted significant interest as a potential source of sustainable biofuel. Mixotrophic microalgae are able to simultaneously photosynthesise while assimilating and metabolising organic carbon. By combining autotrophic and heterotrophic metabolic pathways biomass productivity can be significantly increased. In this study, acetate-fed mixotrophic Micractinium inermum cultures were found to have a specific growth rate 1.74 times the sum of autotrophic and heterotrophic growth. It was hypothesised that gas exchange between the two metabolic pathways within mixotrophic cultures may have prevented growth limitation and enhanced growth. To determine the extent of synergistic gas exchange and its influence on metabolic activity, dissolved inorganic carbon (DIC), dissolved oxygen (DO) and photosynthesis and respiration rates were measured under different trophic conditions. A 32.7 fold and 2.4 fold increase in DIC and DO concentrations, relative to autotrophic and heterotrophic cultures respectively, were coupled with significant increases in rates of photosynthesis and respiration. These data strongly support the hypothesis of mixotrophic gas exchange within M. inermum cultures. In addition to enhanced growth, this phenomenon may provide reductions in aeration and oxygen stripping costs related to microalgae production.     

Mixotrophic cultivation,a preferable microalgae cultivation mode for biomass/bioenergy production,and bioremediation,advances and prospect

Microalgae have received much attention in recent years as a feedstock for producing renewable fuels. Microalgae cultivation technology is one of the main factors restricting biomass production as well as energy fuel production and bioremediation. There are four types of cultivation conditions for microalgae: photoautotrophic, heterotrophic, mixotrophic and photoheterotrophic cultivation. Though photoautotrophic and heterotrophic cultivation are two common growth modes of microalgae, some microalgae can also grow better under mixotrophic condition, which may combine the advantages of autotrophic and heterotrophic and overcome the disadvantages. This review compared these growth modes of microalgae and discussed the advantages of mixotrophic mode in bioenergy production by considering the difference in growth, photosynthesis characteristic and bioenergy production. Also, the influence factors of mixotrophic cultivation and the application of mixotrophic microalgae in bioremediation are discussed, laying theoretical foundation for large scale microalgae cultivating for biomass production, bioenergy production and environmental protection.     

Palm-based biofuel refinery (PBR) to substitute petroleum refinery: An energy and emergy assessment

As the most active palm industry cluster in the world, Malaysia produces enormous amount of biomass from the industry. This work studies the possibility of creating a renewable and sustainable source of energy by fully utilizing an area of land to provide liquid biofuel for the country. Palm-based biofuel refinery (PBR) proposed in this study has the ultimate goal to displace petroleum fuels and fulfill domestic energy demand. It fully utilizes indigenous palm biomass to fulfill 35.5% of energy demand in the country by using land area of only 8% of current palm cultivation. The operation concept of PBR is similar to petroleum refinery in which a single source feedstock (crude petroleum) can be processed to multiple products. In PBR, products from an oil palm plantation will be converted to various biofuel end products. Renewable biofuel such as biodiesel and bioethanol can be produced from crude palm oil and lignocellulosic residues. Energy and emergy assessment were made in this work to evaluate the sustainability and efficiency of PBR. Biofuel produced from PBR has a high energy equivalent of 31.56 MJ/kg as 1 ha of land can produce 182,142 MJ annually. Although there are still obstacles to be overcome, it is important for Malaysia to develop its own energy supply from indigenous resources as an initiative not only for security but also lower carbon emission.     

Two-stage photoautotrophic cultivation to improve carbohydrate production in Chlamydomonas reinhardtii

A two-stage strategy was developed to improve the microalgal carbohydrate accumulation for advanced biofuel production. In the first stage, Chlamydomonas reinhardtii CC125 was cultivated in photo-bioreactors by repeated fed batch operation to improve the biomass production. Optimal culture conditions achieved in the batch operation were applied to the repeated fed batch operation. Biomass productivity reached 0.47 g L⁻¹ d⁻¹ with 70% medium replacement ratio and 5% CO₂ under continuous light of 135 μmol m⁻² s⁻¹. In the second stage, reducing CO₂ content to 0.04% led to a high carbohydrate content of 71%, showing more than 9 times improvement compared to that in the biomass from the first stage culture. These results suggest that photoautotrophic two-stage cultivation is an effective approach to accumulate microalgal carbohydrate as a feedstock for biofuel production.     

Oleaginous yeast Cryptococcus curvatus culture with dark fermentation hydrogen production effluent as feedstock for microbial lipid production

Volatile fatty acids (VFA) from dark fermentation hydrogen production were tested as carbon sources for the culture of oleaginous yeast Cryptococcus curvatus, which is a promising feedstock for biofuel production. The optimal acetate concentration and pH were investigated when potassium acetate was used as the sole carbon source. Comparisons were then made when hydrogen production effluent (HPE) from synthetic wastewater was tested as feedstock. A pH-stat culture fed with acetic acid ultimately produced 168 g/L biomass, with a lipid content of 75.0%. No inhibitor to yeast growth was produced in the hydrogen production process. However, inhibition occurred in culture with HPE from food waste (FW), indicating that inhibitors may be present in the original raw food waste. This inhibition could be avoided by a process that uses glucose as the initial carbon source and then is continuously fed with FW-HPE. The biomass productivity in this continuous culture process reached 0.34 g/L/h, but the lipid content was only 13.5%. These results suggest that FW-HPE alone is not an optimal feedstock, but HPE derived from nitrogen-deficient waste streams could be good feedstocks. This study provides preliminary evidence for the feasibility of using organic waste for the co-production of hydrogen and lipid.     

微藻生物膜去污技术应用研究进展

文章综述了微藻生物膜净化污水和生产生物燃料等方面的国内外最新成果,阐述了典型微藻去污生物膜系统的运行情况、综合效益、优缺点和推广价值,并对微藻生物膜去污技术存在的问题及关键技术进展及发展趋势进行了分析,就微藻生物膜去污技术的规模化及产业化应用提出了建议,以期为微藻生物膜去污技术的成熟和规模应用提供理论和实践支撑。     

Resource demand implications for US algae biofuels production scale-up

Photosynthetic microalgae with the potential for high biomass and oil productivities have long been viewed as a promising class of feedstock for biofuels to displace petroleum-based transportation fuels. Algae offer the additional benefits of potentially being produced without using high-value arable land and fresh water, thereby reducing the competition for those resources between expanding biofuels production and conventional agriculture. Algae growth can also be enhanced by the use of supplemental CO₂ that could be supplied by redirecting concentrated CO₂ emissions from stationary industrial sources such as fossil-fired power plants, cement plants, fermentation industries, and others. In this way, algae may offer an effective means to capture carbon emissions for reuse in renewable fuels and co-products, while at the same time displacing fossil carbon fuels to help bring about a net reduction in overall carbon emissions. Significant displacement of petroleum fuels will require that algae feedstock production reach large volumes that will put demands on key resources. This scenario-based analysis provides a high-level assessment of land, water, CO₂ and nutrient (nitrogen, phosphorus) demands resulting from algae biofuel feedstock production reaching target levels of 10 billion gallons per year (BGY), 20 BGY, 50 BGY, and 100 BGY for four different geographical regions of the United States. Different algae productivities are assumed for each scenario region, where relative productivities are nominally based on annual average solar insolation. The projected resource demands are compared with data that provide an indication of the resource level potentially available in each of the scenario regions. The results suggest that significant resource supply challenges can be expected to emerge as regional algae biofuel production capacity approaches levels of about 10 BGY. The details depend on the geographic region, the target feedstock production volume, and the level of algae productivity that can be achieved. The implications are that the supply of CO₂, nutrients, and water, in particular, can be expected to severely limit the extent to which US production of algae biofuel can be sustainably expanded unless approaches are developed to mitigate these resource constraints in parallel to emergence of a viable algae technology. Land requirements appear to be the least restrictive, particularly in the Western half of the country where larger quantities of potentially suitable classes of land exist. Within the limited scope and assumptions of this analysis, sustainable photosynthetic microalgae biofuel feedstock production in the US in excess of about 10 BGY will likely be a challenge due to other water, CO₂ and nutrient resource limitations. Developing algae production approaches that can effectively use non-fresh water resources and minimize both water and nutrient requirements will help reduce resource constraints. Providing adequate CO₂ resources for enhanced algae production appears the biggest challenge, and could emerge as a constraint at oil production levels below 10 BGY.     

微藻培养方法研究进展

微藻是一种有前景的生物柴油原料。微藻培养是微藻生物柴油生产过程的重要环节。本文就微藻培养方法的研究进展进行了阐述。对自养、异养及兼养三种培养方法进行了比较,并对微藻培养提出了建议。     

Renewable biomass production by mixotrophic algae in the presence of various carbon sources and wastewaters

This study evaluated mixotrophic growth potential of native microalgae in media supplemented with different organic carbon substrates and wastewaters. Three robust mixotrophic microalgae viz. Chlamydomonas globosa, Chlorella minutissima and Scenedesmus bijuga were isolated after long-term enrichments from industrial wastewater. The mixotrophic growth of these microalgae resulted in 3–10 times more biomass production relative to phototrophy. Glucose, sucrose and acetate supported significant mixotrophic growth. Poultry litter extract (PLE) as growth medium recorded up to 180% more biomass growth compared to standard growth medium BG11, while treated and untreated carpet industry wastewaters also supported higher biomass, compared to BG11 growth with no significant effect of additional nitrogen supplementation. Supplementing treated wastewater and PLE with glucose and nitrogen resulted in 2–7 times increase in biomass relative to the unamended wastewaters or PLE. The consortia of Chlamydomonas–Chlorella and Scenedesmus–Chlorella were the best for PLE and untreated wastewater respectively, while a combination all three strains was suitable for both PLE and wastewater. These algae can be good candidates for biofuel feedstock generation as they would not require freshwater or fertilizers. Such mixotrophic algal consortia offer great promise for production of renewable biomass for bioenergy applications using wastewaters.     

Harvesting microalgae by CTAB-aided foam flotation increases lipid recovery and improves fatty acid methyl ester characteristics

Foam flotation is an effective and energy efficient method of harvesting microalgae. This study has investigated the influence of growth phase and lipid content on harvesting efficiency. The highest biomass concentration factors were gained during active culture growth. Surprisingly, the quantities of lipid recovered from microalgae harvested by foam flotation using the surfactant cetyl trimethylammonium bromide (CTAB), were significantly higher than from cells harvested by centrifugation. Further, cells harvested by CTAB-aided foam flotation exhibited a lipid profile more suited to biodiesel conversion containing increased levels of saturated and monounsaturated fatty acids. The enhanced lipid recovery was partially explained by the interaction of the cells with the surfactant, CTAB, which adsorbed onto the algae and was carried over into the total lipid extraction process. However, further evidence also suggested that CTAB promoted in situ cell lysis by solubilising the phospholipid bilayer, thus increasing the amount of extractable lipid. This work demonstrates substantial added value of foam flotation as a microalgae harvesting method beyond energy efficient biomass recovery.     

Mixotrophic cultivation of Chlorella vulgaris and its potential application for the oil accumulation from non-sugar materials

Microbial lipid accumulation to provide alternative oil resources is an exciting research area, obtaining increasing attentions recently for the biodiesel production due to its high production efficiency and less demand of agricultural land. The aim of this study is to optimize the lipid accumulation of Chlorella vulgaris by using various carbon sources in heterotrophic and mixotrophic cultures. Different cultivation factors were studied on their influences to the cell growth and oil accumulation.Our results revealed that C. vulgaris could grow on autotrophic, mixotrophic and heterotrophic modes; and the mixotrophic cultivation especially could produce more cell biomass than the autotrophic or heterotrophic cultures individually or combined. The substrate concentration significantly influenced the final cell yield of the mixotrophic cultivations while the cell lipid content remained relatively constant. Glycerol was inhibitive to the cell growth while the microalgae strain could actively utilize acetate as the carbon source. This provides a promising niche in reducing the overall cost of biofuel production since this substrate can be obtained from some waste processes such as anaerobic digestion.     

Influence of inoculum cell density and carbon dioxide concentration on fed-batch cultivation of Nannochloropsis oculata

The marine microalgae Nannochloropsis oculata is a promising source of biofuel because of its high lipid content. For achieving high productivity of oil from microalgae, a high cell concentration before harvesting is beneficial. The present study investigated fed-batch cultures of N. oculata fed with vitamins and nutrient solutions and found that the biomass yield of N. oculata in the fed-batch culture was 1.25 times higher than that in batch culture. Fed-batch cultivation, especially at high illumination, decreased the inhibitory effect of high carbon dioxide (CO₂) concentration on the microalgal growth. The specific growth rate was directly proportional to the light intensity in the CO₂ environment. A light intensity of 40,000 Lux was able to achieve high specific growth rates in fed-batch cultivation at a CO₂ volume fraction of 2%–15%. The tolerance of N. oculata to CO₂ was enhanced by the daily feeding of nutrients in the fed-batch cultivation. At 2% CO₂, a final cell density of about OD₆₈₂ = 11.4 was achieved in the fed-batch culture in 30 days. Furthermore, a cell density of 14.4 g L⁻¹ was obtained by outdoor fed-batch cultivation in 27 days.     

Hydrogen economy and storage by nanoporous microalgae diatom: Special emphasis on designing photobioreactors

Storing multiple energy forms from microalgae is not only facile but also lowers the cost of culturing the microalgae. Among many microalgae, diatoms are microscopic glass menageries which are responsible for converting stored lipids and biomass into hydrogen, besides fixing 25% of global CO₂. Besides this their silica frustules are also nature's naturally available bionanomaterials which have immense applications in nanotechnology for hydrogen production and other energy storage. The diatom frustules get hybridized with various chemical and biological components to generate or store hydrogen in various fuel cells. In laboratory these live diatoms can be allowed to culture in various designed solar panel photobioreactors better known as diatom solar panels for high and low value-added products essentially biofuel and fucoxanthin. The present review thus discusses about possible scope and approaches to produce hydrogen from live diatom and as well as from its biomass in specially designed photobioreactors. This truly has economic aspects of hydrogen production from diatoms in comparison to other microalgae which needs to be explored for its wide applications due to its robustness and abundance occurrence.     

微藻生物能源研究现状及展望

能源是现代社会发展的命脉,目前仍以化石燃料为主,而对化石燃料过度依赖导致的能源危机和环境问题日益突出,人类需要寻找可再生的清洁能源作为替代能源。微藻作为可持续的生物能源原料,具有巨大的发展潜力。本文综述了微藻原料获取各环节的研究现状,包括微藻育种、规模培养和采收,并重点论述了微藻生物质转化为生物能源产品的研究进展,包括生物柴油、生物乙醇、生物燃气、生物油,同时指出了微藻生物能源未来的研究方向。     

Integration of algae-based biofuel production with an oil refinery: Energy and carbon footprint assessment

Biofuel production from algae feedstock has become a topic of interest in the recent decades since algae biomass cultivation is feasible in aquaculture and does therefore not compete with use of arable land. In the present work, hydrothermal liquefaction of both microalgae and macroalgae is evaluated for biofuel production and compared with transesterifying lipids extracted from microalgae as a benchmark process. The focus of the evaluation is on both the energy and carbon footprint performance of the processes. In addition, integration of the processes with an oil refinery has been assessed with regard to heat and material integration. It is shown that there are several potential benefits of co-locating an algae-based biorefinery at an oil refinery site and that the use of macroalgae as feedstock is more beneficial than the use of microalgae from a system energy performance perspective. Macroalgae-based hydrothermal liquefaction achieves the highest system energy efficiency of 38.6%, but has the lowest yield of liquid fuel (22.5 MJ per 100 MJ_algae) with a substantial amount of solid biochar produced (28.0 MJ per 100 MJ_algae). Microalgae-based hydrothermal liquefaction achieves the highest liquid biofuel yield (54.1 MJ per 100 MJ_algae), achieving a system efficiency of 30.6%. Macro-algae-based hydrothermal liquefaction achieves the highest CO₂ reduction potential, leading to savings of 24.5 resp 92 kt CO_2eq/year for the two future energy market scenarios considered, assuming a constant feedstock supply rate of 100 MW algae, generating 184.5, 177.1 and 229.6 GWh_biochar/year, respectively. Heat integration with the oil refinery is only possible to a limited extent for the hydrothermal liquefaction process routes, whereas the lipid extraction process can benefit to a larger extent from heat integration due to the lower temperature level of the process heat demand.     

Potential of microalgae oil from Dunaliella tertiolecta as a feedstock for biodiesel

Alternative, non-food based biomass fuel feedstock development is vital for our national security, economy and the environment. Microalgae are among the most promising of these alternatives. Microalgal cell growth rates and metabolic products are affected by a combination of environmental parameters. In this work, the influences of light source, light intensity, CO₂ concentration, and photoperiod on the growth of Dunaliella tertiolecta (D. tertiolecta) were studied. The effects of these environmental parameters on the lipid content and fatty acid composition of D. tertiolecta were also investigated. Red light-emitting diodes (LEDs), white LEDs, and fluorescent lights were all found to be effective for algal growth. Increasing light intensity resulted in significantly more rapid algal growth, and increasing the period of light also significantly increased biomass productivity. Similar growth rates were observed for 2%, 4%, and 6% CO₂-concentrations. The different light sources and intensities were found to have no significant effect on FAME composition of D. tertiolecta. Methyl linolenate and methyl palmitate were found to be the major components of FAME produced from D. tertiolecta oil. D. tertiolecta and its derived oils should be a suitable feedstock for biofuel production.     

A comprehensive review on lignocellulosic biomass biorefinery for sustainable biofuel production

The increasingly severe environmental pollution and energy shortage issues have demanded the production of renewable and sustainable biofuels to replace conventional fossil fuels. Lignocellulosic (LC) biomass as an abundant feedstock for second-generation biofuel production can help overcome the shortcomings of first-generation biofuels related to the “food versus fuel” debate and feedstock availability. Embracing the “circular bioeconomy” concept, an integrated biorefinery platform of LC biomass can be performed by employing different conversion technologies to obtain multiple valuable products. This review provides an overview of the principles and applications of thermochemical processes (pyrolysis, torrefaction, hydrothermal liquefaction, and gasification) and biochemical processes (pretreatment technologies, enzyme hydrolysis, biochemical conversion processes) involved in LC biomass biorefinery for potential biofuel applications. The engineering perspective of LC biofuel production on separate hydrolysis and fermentation (SHF), simultaneous saccharification and fermentation (SSF), simultaneous saccharification and co-fermentation (SSCF), and consolidated bioprocessing (CBP) were also discussed.     

基于双氨基粘土絮凝的嗜热微藻采收实验研究

文章将双氨基粘土([MgAC]和[CeAC]的混合物)作为絮凝剂,并研究了[MgAC]和[CeAC]的配用比例和絮凝时间对采收效果的影响。研究结果表明:当[MgAC]与[CeAC]的配比分别为8∶1,5∶1,2∶1和1∶2时,微藻的絮凝效率均可在20 min内达到75%以上;与单独使用[MgAC]或[CeAC]相比,双氨基粘土形成的紧凑网络可在微藻细胞之间进行有效桥接,从而提高微藻采收效率,综合考虑经济性及絮凝效果,确定[MgAC]与[CeAC]的最优配比为8∶1;微藻采收效率与藻液细胞密度有较大关系,过高的藻液细胞密度会使微藻采收效率大大降低;使用双氨基粘土絮凝微藻不会影响微藻培养液的pH值,且双氨基粘土絮凝剂不会影响微藻细胞的生理活性,以及后续的开发应用。     

Enhancing photo fermentative hydrogen production using ethanol rich dark fermentation effluents

The present study demonstrates the feasibility of a two-phase biorefinery process applied to waste substrates producing ethanol rich effluents. The process includes a dark fermentation step followed by photo fermentation and it is able to optimize hydrogen production from waste biomass. The study was conducted using winery wastewater as feedstock. The results indicate that no additional treatments are required when an appropriate dilution of the initial waste is applied. Microbial consortia contained in the winery wastewater promoted a fermentative ethanol pathway. The ethanol rich effluent was converted into hydrogen by phototrophic microorganisms. Despite the presence of inhibiting compounds, the adoption of a mixed phototrophic culture allowed to obtain good results in terms of hydrogen production. Specifically, up to 310 mLH₂ gCOD_consumed^?1 were obtained in the photo fermentative stage. The effectiveness of ethanol rich dark fermentation effluents for hydrogen production enhancement was demonstrated. Noteworthy, polyhydroxybutyrate was also produced during the experiments. The work faces two of the major challenges in the sequential dark fermentation and photo fermentation technology applied to real waste substrates: the minimization of pre-treatments and the enhancement of the hydrogen production yields using ethanol rich DFEs.