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The constantly growing demand for energy and the concern about energy security and the environment motivate the production of fuels and chemicals from different sustainable raw materials. Microalgae are considered for producing third-generation biofuels due to their capacity to grow rapidly and the potential for CO2 fixation. In this context, continuous hydrothermal liquefaction (HTL) of carbohydrate-rich microalga, Chlorella sorokiniana (CS) NIES 2273, and lipid-rich microalga, Chlorella vulgaris (CV) NIES 227, was performed. Then, the bio-oil was hydrotreated (HDT) over sulfided NiW/Al2O3. HTL and HDT oils were characterized by elemental analysis, GPC, 13C and 31P-NMR, SimDis, and GCxGC-MS/FID. In HTL oils, C16 and C18 carboxylic acids were the major components found, reaching 28 wt.% and 34 wt.% of bio-oil from CS and CV, respectively. C16 and C18 fatty amides were also found in both HTL oils, with higher concentrations in the CV bio-oil. These fatty molecules were converted during the hydrotreatment step resulting in a biofuel composed mainly of C15-C18 aliphatics hydrocarbons that felt primarily in the diesel range. The bio-oil from CV showed a lower aromaticity degree, lower O/C and N/C ratio, and higher H/C ratio, whereas the bio-oil from CS was more challenging to upgrade and showed higher amounts of cyclic oxygen and nitrogen compounds, such as phenols and pyrroles. Three times higher amounts of lipids in the CV microalgae led to three times higher biofuel production. Lastly, analysis of the used hydrotreating catalysts showed iron accumulation on both catalysts after upgrading and a similar coke structure. more...

Hydroponic farms produce wastewater that need to be treated before being released into the environment. A three-step screening process (microplate, batch, and semi-continuous flasks experiments) initially designed to select an efficient microalgae strain allowed the isolation of a consortium that naturally developed in the hydroponic farm wastewater. During the non-optimized semi-continuous experiments, the best performing microalgae strain, Scenedesmus obliquus UTEX393 and the wastewater-born consortium cultures achieved good average linear growth rate (0.186 and 0.198/d, respectively) and high average nitrogen removal rates (23.5 mgN/L/d and 21.9 mgN/L/d, respectively). Phosphorus removal was very high probably due to precipitation. An integrated process was designed to treat the hydroponic farm wastewater using the wastewater-born consortium. Despite relatively low coagulation efficiencies in the preliminary tests, when integrated in a continuous process, chitosan was efficient to harvest the naturally wastewater-born consortium. The process was also efficient for removing nitrate and phosphate in less than seven days (average removal of 98.2 and 87.1% for nitrate and phosphate, respectively). These very promising results will help to define a pre-industrial pilot process. more...

International audience; Microalgae were considered in this work as a new resource for developing starch-based bioplastics. Ten green microalgae strains were screened at lab-scale for their ability to produce starch. A long run (800 h) two-stage accumulation strategy was designed with successive cultivation in sulfur-replete, then sulfur-depleted medium in autotrophic conditions. Starch content was assessed on cell lysate by enzymatic digestion of extracted starch into glucose. Chlamydomonas reinhardtii 11-32A strain was selected as it displayed a maximum starch-to-biomass ratio of 49% w/w, 460 h after being switched to a sulfur-deprived medium. Small-scale pilot production (30 L tubular photobioreactor) with C. reinhardtii 11-32A yielded sufficient biomass quantity to investigate its direct plasticization with glycerol in a twin-screw extruder. Microstructural characterization confirmed the ability for starch-enriched microalgae to be homogeneously plasticized, and hence the possibility to use microalgae as a new platform for the development of bioplastics. more...

The industrial production of microalgae is profitable for specific applications, either very high-value molecules such as nutraceuticals (e.g., omega 3, 522carotenoids) or whole microalgae produced using a low-cost process such as fish larva feed for aquaculture or Spirulina as a dietary supplement. However, producing biofuel or building block molecules for the chemical industry with microalgae is not economically viable at the moment. For this kind of nonmature technology, techno-economic analyzes (TEA) can be of great help regarding two main ambitions: (i) many process options are to be explored especially for microalgae biofuel production and TEA is a practical tool for comparing them on similar bases. The process pathways with the best potential can then be specified, and (ii) sensitivity analyzes of TEA can identify key parameters and processes on which research efforts need to be addressed in order to decrease the production cost or improve the energetic and environmental balances. The first TEAs on microalgae biofuel production have pointed out the drying as the most energy intensive step in the process. Since then, wet conversion processes such as hydrothermal liquefaction or wet lipid extraction have been preferred. Microalgae cultivation is the step with the highest impact on the economics of the whole biofuel production process. Reducing its cost is a major and crucial challenge. Sensitivity analyzes have shown that microalgae productivity is the most important factor for economically and energetically viable microalgae biofuel production. This validates the actual research efforts on screening and selecting highly efficient microalgae strain. In the context of a difficult economic viability, the use of waste streams (i.e., wastewaters for nutrients and flue gases for CO2) and the recycling of process waters are strongly recommended. The biorefinery concept needs to be applied to the microalgae biofuel production process. Similarly, the valorization of the entire biomass is needed. Co-products such as pigments or omega 3 can be of great help to make the process profitable, especially now, at an early stage of the microalgae biofuel industry. However, when the full-scale of microalgae biofuel production will be reached, the market sizes of biofuel and these high-value molecules will not be compatible. At that time, animal feed, human food and bioremediation will emerge as serious covalorization opportunities. more...

Renewable diesel productions through HTL (hydrothermal liquefaction) and pyrolysis of Chlamydomonas reinhardtii were compared based on energetic and economic evaluation. The whole biofuel production pathway was simulated, from the microalgae cultivation step to the upgrading of the bio-oil. Alternative dewatering technologies were evaluated to decrease the energy consumption and the bio-diesel cost. Thermochemical models were developed for both HTL and pyrolysis of C. reinhardtii based on experimental results. The pathways using heat exchangers between the inlet and outlet of the HTL reactor were the only scenarios to be net energy producers. The other pathways consumed more energy than they produced. The costs of production of renewable diesel from HTL or pyrolysis were significantly higher than petroleum diesel (average of 70.4 €/GJ). The most expensive step was the microalgae cultivation (nutrients cost and raceway capital cost). more...

article i nfo Coagulation-flocculation is an efficient, economic, and scalable process suitable for harvesting microalgae. The study tested the effectiveness of 11 agents (chitosan and 10 commercial, industrially available reference prod- ucts) forharvestingChlamydomonas reinhardtii,a modelmicroalga.The highest efficiencies(N95%)with the low- est dose (b30 g/kg of biomass for 2 of the 4 polymers tested) were achieved for highly charged cationic polyacrylamides with a high molecular weight. Mineral coagulants were less efficient. Efficiencies above 80% were attained for 2 out of 4 flocculants with doses ranging from 40 to 80 g/kg of dry biomass. Chitosan appeared tobea goodalternative to polyacrylamides; itattainedan efficiency of over90%fora 35g/kgdoseof drybiomass. The study further investigated a reuse of the supernatant resulting from the solid-liquid separation, an essential prerequisite to scale up the process. Two types of cultivation tests were performed for three selected—chitosan, polyaluminium chlorosulfate, and an 80% cationic polyacrylamide: 1) using various ratios of supernatant to fresh medium and 2) using various concentrations of flocculant in a fresh medium. These preliminary experiments showedthat flocculantresiduesalterthegrowth ofC. reinhardtii indifferent waysdepending onthe chemicalna- ture and concentration of the considered flocculant. No lethal toxicity was observed. more...

Arthrospira platensis (Spirulina) is the most cultivated microalga worldwide. Improving its cultivation in terms of biomass productivity, quality, or production cost could significantly impact the Spirulina industry. The objectives of this paper were defined as to contribute to this goal. Spirulina biomass productivity was investigated through medium choice. A modified Zarrouk’s medium was selected as it gave higher final dry weights and longer sustained growth than Hiri’s and Jourdan’s media. Then, in order to reduce Spirulina production cost, modified Zarrouk’s medium was rationalized by testing different dilutions. It was found that modified Zarrouk’s medium could be diluted up to five times without impacting the growth rates in a 28-days batch cultivation. Higher dry weights were even observed after 21 days of batch cultivation (1.21 g/L for 20%-modified Zarrouk’s medium in comparison to 0.84 g/L for modified Zarrouk’s medium). Iron uptake was then investigated as one of the major contributors to Spirulina nutritional quality. An increase in iron content was obtained by replacing iron sulfate by iron EDTA at a concentration of 10 mgFe/L (2.11 ± 0.13 mgFe/gbiomass for EDTA-FeNa, 3 H2O at 10 mgFe/L compared to 0.18 ± 0.13 for FeSO4,6H2O at 2 mgFe/L). Impact of light intensity on Spirulina biomass productivity was also investigated in a 2 L Photobioreactor (PBR). Specific growth rates were calculated for Photosynthetically Photon Flux Densities (PPFD) from 85 to 430 µmol/m2/s. At 430 µmol/m2/s, photoinhibition was not observed and the specific growth rate was maximum (0.12/day). Finally, a 40-day cultivation experiment was conducted in a 1000 L PBR giving a maximum daily areal productivity of 58.4 g/m2/day. A techno-economic analysis gave production cost two to 20 times higher for PBR (from 18.71 to 74.29 €/kg) than for open ponds (from 3.86 to 9.59 €/kg) depending on Spirulina productivity. more...

This study aims at comparing the steam gasification behaviour of two species of algal biomass (Chlamydomonas reinhardtii and Arthrospira platensis) and three species of lignocellulosic biomass (miscanthus, beech and wheat straw). Isothermal experiments were carried out in a thermobalance under chemical regime. Samples had very different contents in inorganic elements, which resulted in different reactivities, with about a factor of 5 between samples. For biomasses with ratio between potassium content and phosphorus and silicon content K/(Si + P) higher than one, the reaction rate was constant during most of the reaction and then slightly increased at high conversion. On the contrary, for biomasses with ratio K/(Si + P) lower than one, the reaction rate decreased along conversion. A simple kinetic model was proposed to predict these behaviours. more...

International audience; Measuring biofuel sustainability requires dealing with a wide variety of complex and conflicting values at stake. Consequently, the biofuel capacity to contribute to one specific value cannot lead to any absolute conclusion about the overall sustainability of biofuel. The scope of the sustainability concept may vary depending on individuals' preferences, the time scale and the geographical region. Based on the 5 pillars sustainability concept that includes social, economic, environmental, legal and cultural considerations, the present study proposes to assess several biofuel sustainability options for France by 2030 through a stakeholder-driven approach. Rather than seeking to reach a consensus, our approach allows us to capture the wide diversity of stakeholders' perspectives and preferences. French stakeholders perceive 22 different sustainability criteria for biofuels with a very low level of agreement between the different segments of professions (feedstock producers, biofuel producers, refining industry, fuel distributors, car manufacturers, end-users, government and NGOs). In order to operationalize the sustainability assessment, a set of indicators has been identified with stakeholders that allows us to measure the capacity of biofuels to fulfill each of their criteria. Seventeen biofuel options were assessed with regards to economic, social, environmental, cultural and legal considerations, allowing the identification of the strengths and weaknesses of each biofuel. more...

A new process evaluation methodology of microalgae biodiesel has been developed. Based on four evaluation criteria, i.e. the net energy ratio (NER), biodiesel production costs, greenhouse gases (GHG) emission rate and water footprint, the model compares various technologies for each step of the process, from cultivation to oil upgrading. An innovative pathway (hybrid raceway/PBR cultivation system, belt filter press for dewatering, wet lipid extraction, oil hydrotreating and anaerobic digestion of residues) shows good results in comparison to a reference pathway (doubled NER, lower GHG emission rate and water footprint). The production costs are still unfavourable (between 1.94 and 3.35 €/L of biodiesel). The most influential parameters have been targeted through a global sensitivity analysis and classified: (i) lipid productivity, (ii) the cultivation step, and (iii) the downstream processes. The use of low-carbon energy sources is required to achieve significant reductions of the biodiesel GHG emission rate compared to petroleum diesel. more...

In view of the increasing demand for bioenergy, in this study, the techno-economic viabilities for three emerging pathways to microalgal biofuel production have been evaluated. The three processes evaluated are the hydrothermal liquefaction (HTL), oil secretion and alkane secretion. These three routes differ in their lipid extraction procedure and the end-products produced. This analysis showed that these three processes showed various advantages: possibility to convert the defatted microalgae into bio-crude via HTL thus increasing the total biodiesel yield; better energetic and environmental performance for oil secretion and an even increased net energy ratio (NER) for alkane secretion. However, great technological breakthroughs are needed before planning any scale-up strategy such as continuous wet biomass processing and heat exchange optimization for the HTL pathway and effective and sustainable excretion for both secretion pathways. more...

[Departement_IRSTEA]Ecotechnologies [TR1_IRSTEA]TED [Axe_IRSTEA]TED-EPURE; International audience; A full-scale membrane bioreactor (1600 m3.d-1) was monitored for modelling purposes during the summer of 2006. A complete calibration of the ASM1 model is presented, in which the key points were the wastewater characterisation, the oxygen transfer and the biomass kinetics. Total BOD tests were not able to correctly estimate the biodegradable fraction of the wastewater. Therefore the wastewater fractionation was identified by adjusting the simulated sludge production rate to the measured value. MLVSS and MLSS were accurately predicted during both calibration and validation periods (20 and 30 days). Because the membranes were immerged in the aeration tank, the coarse bubble and fine bubble diffusion systems coexisted in the same tank. This allowed five different aeration combinations, depending whether the 2 systems were operating separately or simultaneously, and at low speed or high speed. The aeration control maintained low DO concentrations, allowing simultaneous nitrification and denitrification. This made it difficult to calibrate the oxygen transfer. The nitrogen removal kinetics were determined using maximum nitrification rate tests and an 8-hour intensive sampling campaign. Despite the challenges encountered, a calibrated set of parameters was identified for ASM1 that gave very satisfactory results for the calibration period. Matching simulated and measured data became more difficult during the validation period, mainly because the dominant aeration configuration had changed. However, the merit of this study is to be the first effort to simulate a full-scale MBR plant. more...

Microalgae have been shown to be a source of multiple bio-based products ranging from high value molecules to commodities. Along with their potential to produce a large variety of products, microalgae can also be used for the depollution of wastewaters of different origins (urban, industrial, and agricultural). This paper is focused on the importance of harnessing the bioremediation capacity of microalgae to treat wastewaters in order to develop the microalgae industry (especially the microalgae biofuel industry) and to find other alternatives to the classic wastewater treatment processes. The current research on the potential of microalgae to treat a specific wastewater or a targeted pollutant is reviewed and discussed. Then, both strategies of selecting the best microalgae strain to treat a specific wastewater or pollutant and using a natural or an artificial consortium to perform the treatment will be detailed. The process options for treating wastewaters using microalgae will be discussed up to the final valorization of the biomass. The last part is dedicated to the challenges which research need to address in order to develop the potential of microalgae to treat wastewaters. more...