While research and development of algal biofuels are currently receiving much interest and funding, they are still not commercially viable at today’s fossil fuel prices. However, a niche opportunity may exist where algae are grown as a by-product of high rate algal ponds (HRAPs) operated for wastewater treatment. In addition to significantly better economics, algal biofuel production from wastewater treatment HRAPs has a significantly smaller environmental footprint compared to commercial algal production HRAPs which consume freshwater and fertilizers. In this paper the critical parameters that limit algal cultivation, production and harvest are reviewed and practical options that may enhance the net harvestable algal production from wastewater treatment HRAPs including CO2 addition, species control, control of grazers and parasites and bioflocculation are discussed.
To avoid negative impacts on food production, novel non-food biofuel feedstocks need to be identified and utilised. One option is to utilise marine biomass, notably fast-growing, large marine ‘plants’ such as the macroalgal kelps. This paper reports on the changing composition of Laminaria digitata throughout it growth cycle as determined by new technologies. The potential of Laminaria sp. as a feedstock for biofuel production and future biorefining possibilities was assessed through proximate and ultimate analysis, initial pyrolysis rates using thermo-gravimetric analysis (TGA), metals content and pyrolysis gas chromatography-mass spectrometry.
Samples harvested in March contained the lowest proportion of carbohydrate and the highest ash and alkali metal content, whereas samples harvested in July contained the highest proportions of carbohydrate, lowest alkali metals and ash content. July was therefore considered the most suitable month for harvesting kelp biomass for thermochemical conversion to biofuels.
Population outburst together with increased motorization has led to an overwhelming increase in the demand for fuel. In the milieu of economical and environmental concern, algae capable of accumulating high starch/cellulose can serve as an excellent alternative to food crops for bioethanol production, a green fuel for sustainable future. Certain species of algae can produce ethanol during dark-anaerobic fermentation and thus serve as a direct source for ethanol production. Of late, oleaginous microalgae generate high starch/cellulose biomass waste after oil extraction, which can be hydrolyzed to generate sugary syrup to be used as substrate for ethanol production. Macroalgae are also harnessed as renewable source of biomass intended for ethanol production. Currently there are very few studies on this issue, and intense research is required in future in this area for efficient utilization of microalgae and their industrial wastes to produce environmentally friendly fuel bioethanol.
A range of model biochemical components, microalgae and cyanobacteria with different biochemical contents have been liquefied under hydrothermal conditions at 350 degrees C, approximately 200bar in water, 1M Na(2)CO(3) and 1M formic acid. The model compounds include albumin and a soya protein, starch and glucose, the triglyceride from sunflower oil and two amino acids. Microalgae include Chlorella vulgaris,Nannochloropsis occulata and Porphyridium cruentum and the cyanobacteria Spirulina. The yields and product distribution obtained for each model compound have been used to predict the behaviour of microalgae with different biochemical composition and have been validated using microalgae and cyanobacteria. Broad agreement is reached between predictive yields and actual yields for the microalgae based on their biochemical composition. The yields of bio-crude are 5-25wt.% higher than the lipid content of the algae depending upon biochemical composition. The yields of bio-crude follow the trend lipids>proteins>carbohydrates.
Due to resource depletion and climate change, lipid-based algal biofuel has been pointed out as an interesting alternative because of the high productivity of algae per hectare and per year and its ability to recycle CO2 from flue gas. Another option for taking advantage of the energy content of the microalgae is to directly carry out anaerobic digestion of raw algae in order to produce methane and recycle nutrients (N, P and K). In this study, a Life-Cycle Assessment (LCA) of biogas production from the microalgae Chlorella vulgaris is performed and the results are compared to algal biodiesel and to first generation biodiesels. These results suggest that the impacts generated by the production of methane from microalgae are strongly correlated with the electric consumption. Progresses can be achieved by decreasing the mixing costs and circulation between different production steps, or by improving the efficiency of the anaerobic process under controlled onditions. This new bioenergy generating process strongly competes with others biofuel productions.
We describe a methodology to investigate the potential of given microalgae species for biodiesel production by characterising their productivity in terms of both biomass and lipids. A multi-step approach was used: determination of biological needs for macronutrients (nitrate, phosphate and sulphate), determination of maximum biomass productivity (the “light-limited” regime), scaling-up of biomass production in photobioreactors, including a theoretical framework to predict corresponding productivities, and investigation of how nitrate starvation protocol affects cell biochemical composition and triggers triacylglycerol (TAG) accumulation. The methodology was applied to two freshwater strains, Chlorella vulgaris and Neochloris oleoabundans, and one seawater diatom strain, Cylindrotheca closterium. The highest total lipid content was achieved with N. oleoabundans (25–37% of DW), while the highest TAG content was found in C. vulgaris (11–14% of DW). These two species showed similar TAG productivities.
Microalgae possess the potential to produce bio-oils, carbohydrates, protein, amino acids and other value added products, each of which increase its value as a crop. Unfortunately, proven systems do not yet exist for commercial scale production. System designs have generally not adequately accounted for water and energy use at scale, as well as byproduct markets, and thus yielded systems that are both unaffordable and unsustainable. We address energy and water use by presenting a straightforward microalga-to-bio-oil production process and then characterize system performance using steady-state water and energy balances. Practical limitations to commercial production of bio-oils from photosynthetic microalgae are proposed and conclusions drawn regarding system potential for assumed biomass productivities. As this is a theoretical analysis of a generic process and in practice many of the bottlenecks presented remain to be solved. It is our intent that the analysis framework presented herein can be applied to future systems that propose such solutions.
The main goal of this present study is to investigate the feasibility of coupling algae production (Chlorella vulgaris) to an anaerobic digestion unit. An intermediate settling device was integrated in order to adapt the feed-flow concentration and the flow-rate. Digestion of C. vulgaris was studied under 16 and 28 days Hydraulic Retention Times (HRT), with a corresponding organic loading rate of 1gCOD.L-1. Increasing the HRT achieved 51% COD removal with a methane production measured at 240 mL.gVSS-1. Performing different HRTs and dynamic monitoring during degradation highlighted differential hydrolysis of microalgae compartments. However, 50% of the biomass did not undergo anaerobic digestion, even under long retention times. This points out the interest for further studies on pre-treatment performances and more generally speaking on the need for intensifying microalgae biomass digestion.
To obtain a detailed picture of sulphur deprivation induced H2 production in microalgae, metabolome analyses were performed during key time points of the anaerobic H2 production process of Chlamydomonas reinhardtii. Analyses were performed using gas chromatography coupled to mass spectrometry (GC/MS), two dimensional gas chromatography combined with time of flight mass spectrometry (GCxGC TOFMS), lipid and starch analysis and enzymatic determination of fermentative products. The studies were designed to provide a detailed metabolite profile of the Solar Bio H2 production process. This work reports on the differential analysis of metabolic profiles of the high H2 producing strain Stm6Glc4 and the wild type cc406 (WT) before and during the H2 production phase. Using GCxGC TOFMS analysis the number of detected peaks increased from 128 peaks, previously detected by GC/MS techniques, to approx. 1168. More detailed analysis of the anaerobic H2 production phase revealed remarkable differences between wild type and mutant cells in a number of metabolic pathways. Under these physiological conditions the WT produced up to 2.6 times more fatty acids, 2.2 times more neutral lipids and up to 4 times more fermentation products compared to Stm6Glc4. Based on these results, specific metabolic pathways involving the synthesis of fatty acids, neutral lipids and fermentation products during anaerobiosis in C. reinhardtii have been identified as potential targets for metabolic engineering to further enhance substrate supply for the hydrogenase(s) in the chloroplast.
This study was carried out to investigate the membrane fouling phenomena due to algal deposition and to understand the nature of the cake deposited on the membrane while treating the algae-laden water by membrane filtration. To accomplish this, batch experiments in dead end mode were carried out using Chlorella algae to investigate the effect of feed concentration and transmembrane pressure (TMP) on cake resistance using cellulose ester and polyvinylidene difluoride (PVDF) membranes. It was found that algae can cause significant fouling of both the cellulose ester and PVDF membranes. Fouling due to algae is quite complex because these cells release extracellular organic matter (EOM) which significantly increases the resistance. The cake resistance offered by the Chlorella algae was independent of the membrane materials considered; thus the interaction between the membrane material and Chlorella cells was not important in the resistance development. It was also found that the cake deposited on the membrane was compressible in nature with a compressibility index of 0.439.
This paper analyses the potential environmental impacts and economic viability of producing biodiesel from microalgae grown in ponds. A comparative Life Cycle Assessment (LCA) study of a notional production system designed for Australian conditions was conducted to compare biodiesel production from algae (with three different scenarios for carbon dioxide supplementation and two different production rates) with canola and ULS (ultra-low sulfur) diesel. Comparisons of GHG (greenhouse gas) emissions (g CO2-e/t km) and costs (¢/t km) are given. Algae GHG emissions (−27.6 to 18.2) compare very favourably with canola (35.9) and ULS diesel (81.2). Costs are not so favourable, with algae ranging from 2.2 to 4.8, compared with canola (4.2) and ULS diesel (3.8). This highlights the need for a high production rate to make algal biodiesel economically attractive.
The potential of microalgae as a source of renewable energy has received considerable interest, but if microalgal biofuel production is to be economically viable and sustainable, further optimization of mass culture conditions are needed. Wastewaters derived from municipal, agricultural and industrial activities potentially provide cost-effective and sustainable means of algal growth for biofuels. In addition, there is also potential for combining wastewater treatment by algae, such as nutrient removal, with biofuel production. Here we will review the current research on this topic and discuss the potential benefits and limitations of using wastewaters as resources for cost-effective microalgal biofuel production.
The aim of this study is to investigate the algae production technologies such as open, closed and hybrid systems, production costs, and algal energy conversions. Liquid biofuels are alternative fuels promoted with potential to reduce dependence on fossil fuel imports. Biofuels production costs can vary widely by feedstock, conversion process, scale of production and region. Algae will become the most important biofuel source in the near future. Microalgae appear to be the only source of renewable biodiesel that is capable of meeting the global demand for transport fuels. Microalgae can be converted to bio-oil, bioethanol, bio-hydrogen and bimethane via thermochemical and biochemical methods. Microalgae are theoretically very promising source of biodiesel.
Abstract Cost-effective implementation of microalgae as a solar-to-chemical energy conversion platform requires extensive system optimization; computer modeling can bring this to bear. This work uses modified versions of the U.S. Environmental Protection Agency's (EPA's) Environmental Fluid Dynamics Code (EFDC) in conjunction with the U.S. Army Corp of Engineers' water-quality code (CE-QUAL) to simulate hydrodynamics coupled to growth kinetics of algae (Phaeodactylum tricornutum) in open-channel raceways. The model allows the flexibility to manipulate a host of variables associated with raceway-design, algal-growth, water-quality, hydrodynamic, and atmospheric conditions. The model provides realistic results wherein growth rates follow the diurnal fluctuation of solar irradiation and temperature. The greatest benefit that numerical simulation of the flow system offers is the ability to design the raceway before construction, saving considerable cost and time. Moreover, experiment operators can evaluate the impacts of various changes to system conditions (e.g., depth, temperature, flow speeds) without risking the algal biomass under study.
Un rapport publié par IEA Bioenergy. Le rapport énumère les principes chimiques de production de biodiesel mais également des méthodes qui ne sont pas utilisées sur le marché. La partie principale de ce rapport décrit les technologies les plus couramment employées. Ces descriptions sont basées sur des réponses à un questionnaire standardisé ainsi que des discussions avec les entreprises. Des questionnaires ont été envoyés aux fournisseurs de technologie qui avait déjà réalisé un certains nombres d'installations de production. Les informations obtenues ont été condensées dans les descriptions de la technologie des procédés, comprenant la liste des étapes du processus, sources de matières premières appropriées et qualités, et la qualité du produit fini (le biodiesel). Les coordonnées complètes des fournisseurs de technologies et de centrales de référence sont énumérées.
Today’s society relies heavily on fossil fuels as a main energy source. Global energy demand increase, energy security and climate change are the main drivers of the transition towards alternative energy sources. This paper analyses algal biodiesel production for the EU road transportation and compares it to the fossil fuels and 1st generation biofuels. A cost-effectiveness analysis was used to aggregate private and external costs and derive the social cost of each fuel. The following externalities were internalized: emissions (GHG and non-GHG), food prices impact, pesticides/fertilizers use and security of supply. Currently the social cost of producing algal biodiesel at 52.3 € GJ−1 is higher than rapeseed biodiesel (36.0 € GJ−1) and fossil fuels (15.8 € GJ−1). Biotechnology development, high crude oil prices and high carbon value are the key features of the scenario where algal biodiesel outcompetes all other fuels. A substantial investment into the biotechnology sector and comprehensive environmental research and policy are required to make that scenario a reality.
Photosynthetic microorganisms could serve as valuable compounds, but also for environmental applications. Their production under controlled conditions implies to design specific reactors, named photobioreactors, in which light supply is the main constraint. This paper was devoted to an original external-loop airlift photobioreactor (PBR) with annular light chambers in which a swirling motion was induced. The aim was to characterize this novel geometrical configuration in terms of gas-liquid hydrodynamics, and to test its potentiality for algal cultures. This PBR consisted of two identical columns connected by flanges defining tangential inlets, each column being made of two transparent concentric tubes (6 L in liquid volume, 50 m−1 in specific illuminated area). Firstly, the global flow characteristics (circulation and mixing times) were determined by a tracer method and modelled by an axial dispersed plug flow with complete recirculation (Péclet number). By means of a double optical probe, both local and global time-averaged parameters of the gas phase were measured, namely void fraction, bubble velocity, frequency and size. The gas-liquid mass transfer were also characterized, in tap water and in culture medium, by measuring overall volumetric mass transfer coefficients. In a second time, cultures of the microalga Chlamydomonas reinhardtii were run in batch mode. The variations of biomass concentration and pigment content with time from inoculation were successfully obtained. All these findings highlighted: (i) some significant differences in terms of gas-liquid hydrodynamics between the present PBR and the usual airlift systems, (ii) the interest of this configuration for algal cultures, even if complementary studies and technological improvements are still required for definitively validating its scale-up.
Unbalanced production of atmospheric CO2 constitutes a major challenge to global sustainability. Technologies have thus been developed for enhanced biological carbon fixation (also referred to as CO2 mitigation), and one of the most promising capitalizes on microalgae. However, the “best bioreactor”, which would be able to achieve maximum productivity and maximum energy efficiency under a given set of operational costs, does not exist. This review briefly examines the current technologies available for enhanced microalgal CO2 fixation, and specifically explores the possibility of coupling wastewater treatment with microalgal growth for eventual production of biofuels and/or added-value products, with an emphasis on productivity. In addition, an overview of reactor configurations for CO2 fixation and bottlenecks associated with the underlying technology are provided. Finally, a review of life cycle analysis studies is presented, and routes for improvement of existing processes are suggested.
La maison mère d'Airbus a réussi à faire voler un avion avec un carburant dérivé à 100% d'algues. L'avionneur estime que les biocarburants pourraient représenter jusqu'à 30% du carburant avion utilisé d'ici à 2030.