• Energy Research

Production of microalgae biomass as an alternative feedstock for biodiesel is a promising technology. The reduction in energy consumption of traditional algae cultivation systems is today one of the most important issues towards sustainable biofuel production. In the MAMBO project an innovative pond has been designed and realized to investigate the possibility of reducing energy consumption of the cultivation phase as well as the use of water. The aim of this project is in fact to demonstrate the possibility of using algae as an alternative and cost­effective feedstock for the biodiesel industry. The innovation is based on the reduction of the mean fluid velocity in the pond and the reduction of the water head, while maintaining sufficient turbulence and recirculation of the culture. The typical energy demand for mixing in a traditional raceway pond, operated at 20 cm depth and 20 cm/s speed, is estimated in 0.034 W/m2. The reduction in fluid velocity has a large impact on the energy demand of the cultivation phase (essential in view of biofuel production), nevertheless the major drawback is that it also reduces the effectiveness of mixing, which is a key factor to obtain high productivity per unit area. A reduced culture depth also offers the advantage of a lower amount of water needed per square meter of pond maintaining the same area for solar energy input and leads to higher algae concentration in the fluid medium. Injection and solubilisation of carbon dioxide in the fluid stream also deserve attention. Systems have been developed in the innovative pond to avoid or reduce uneconomical CO2 losses. The real flow field in both the traditional and the innovative ponds was evaluated by velocimetry measurement under actual operation conditions. The methodology adopted in this research work was based on a combination of numerical and experimental activities. A numerical tool was designed to estimate the effect of the reduction in fluid velocity and culture depth on energy consumption and mixing. The results obtained from numerical simulations were then used in designing the innovative pond and defining the main operational parameters and characteristics. Tests on the traditional raceway pond and on the innovative one were carried out during summer 2010 in Florence (Italy). The on­field collected data were elaborated linking microalgae productivity to solar input and energy consumption. The preliminary results obtained during the first year of experimentation showed that the innovative pond has a slightly lower productivity compared to the traditional pond, but needs significantly less energy and water. The solutions tested in this research is already interesting in all the country where water is a precious resource and land is often not yet profitably used. Proceedings of the 19th European Biomass Conference and Exhibition, 6-10 June 2011, Berlin, Germany, pp. 90-93

The energy balance of microalgal biodiesel production is rarely considered. Besides, the actual potential of microalgae as triglyceride producers is often overestimated. This work was aimed at investigating these critical aspects using the marine eustigmatophyte Nannochloropsis sp. F&M‐M24, a promising oil producing strain, as model organism and the “Green Wall Panel” as culture system. First, the influence of air‐flow rate on volumetric productivity of the microalga was evaluated. At low and medium irradiances, no significant differences in productivity occurred at the three different mixing rates tested, while at high irradiances an increase in the air‐flow rate resulted in significantly higher volumetric productivities. These results allow to foresee a strategy of air‐flow rate tuning in accordance to radiation, that may lead to substantial energy savings and, consequently, to more favorable energy and economic balances in the cultivation process. Second, the lipid content and fraction distribution of the biomasses produced under nutrient sufficient and nitrogen‐starved conditions were analyzed and the neutral lipid fraction was fully characterized. Finally, the alga was grown in bubbled‐tubes using a culture medium prepared with an industrial wastewater, to evaluate its ability to use a free of charge source of nutrients, the exploitation of which may improve biomass production economics. © 2012 American Institute of Chemical Engineers Environ Prog, 32: 846–853, 2013

he MAMBO project, supported by several Italian biodiesel producers (led by NOVAOL) and their associations Assocostieri, addresses the production of microalgae for biodiesel production. Given the large scale of the biofuel market, raceway ponds have been considered as an unavoidable component of any industrial system aimed at producing biomass derived fuels in sufficient amounts. Nevertheless, innovation in raceway pond design has been very limited in recent years,maybe due to the high price (and low volume) of the current commercial microalgae-derived products, and therefore a modest interest in reducing costs of these productions. Among various activities, MAMBO focused its investigation on key issue for raceway pond design, and the possibility of improving their performances in terms of energy demand and microalgae concentration for downstream processes. Two pilot units have been designed, built and operated, to achieve a better understanding of the flow field and the microalgae behavior during cultivation. A reference traditional raceway pond has also been constructed, to compare and validate results, and hotobioreactors were also operated in parallel so to have a further comparison. A preliminary analysis identified a number of key elements to be considered before re-designing the raceway pond, such as culture depth, fluid flow, turbulence and mixing, heat exchange, and CO2 addition. A number of theoretical and experimental activities have been implemented to identify the optimum solutions. Then, microalgae have been cultivated under these innovative conditions. Results from the experimental campaign confirmed the possibility of achieving a considerable reduction of both energy demand (reduced by ~75% up to ~90% substituting the paddle wheel system) and water use (reduced by ~50%), a significant step forward in microalgae cultivation. This innovative approach will also facilitate the downstream biofuel production processes.

RATIONALEDue to their health benefits, there is growing interest in the production and use of carotenoids from natural sources, e.g. microalgae. To date, only Haematococcus pluvialis and Dunaliella, that accumulate, respectively, astaxanthin and β‐carotene in large quantities, are grown commercially. However, interest is also being focused on other xanthophylls, such as (all‐E)‐fucoxanthin characterized by anti‐obesity and anti‐carcinogenic effects. In this regard, rigorous chemical and analytical techniques following preparative isolation of components are needed to unequivocally identify individual carotenoids in microalgae.METHODSThe carotenoid profile of Isochrysis sp. biomass, produced in closed photobioreactors, was determined by reversed‐phase C30 (RP‐30) high‐performance liquid chromatography coupled with diode‐array detector mass spectrometry using positive electrospray ionization (HPLC/DAD‐MS/ESI+) analysis. Additionally, multistage mass spectrometry (MSn) analyses, together with fine structures of the UV–vis spectra, were used to differentiate structural and geometrical isomers.RESULTSThis technique allowed the simultaneous determination of geometrical, isomers of fucoxanthin (all‐E‐fucoxanthin, 13Z‐, 13'Z‐ and 9'Z‐fucoxanthin), diatoxanthin and 5,8‐epoxydiadinoxanthin diasteroisomers (R/S). The analyzed extracts contained fucoxanthin isomers as the major carotenoids and, in particular, (all‐E)‐fucoxanthin was the main geometrical isomer (~̴ 85%) found at a concentration of 17 mg/g of the lyophilized biomass.CONCLUSIONSConsidering the high content of fucoxanthin in Isochrysis sp. biomass, the microalga could be proposed as a source of this compound for nutraceutical and pharmaceutical applications. Copyright © 2013 John Wiley & Sons, Ltd.

The marine microalga Nannochloropsis sp. has been cultivated outdoors in a 600-L “Green Wall Panel” and the quality and quantity of the produced fat evaluated in view of biodiesel production. Lipid extracts were characterized in terms of lipid distribution between neutral and polar lipids as well as phospholipids. The results obtained by analyzing two samples of Nannochloropsis sp. grown in normal feeding conditions or in nitrogen deprived medium are reported. Some considerations about the design of open ponds for mass cultivation of microalgae and the relationships existing between biomass production and energy consumption are also discussed. Proceedings of the 18th European Biomass Conference and Exhibition, 3-7 May 2010, Lyon, France, pp. 538-541

Abstract The current high interest in the algae sector is leading to the development of several demo/commercial scale projects, either for the food market or bioenergy production. Raceway Ponds (RWPs) are a widely used technology for algae mass cultivation. RWPs were developed long time ago, and thus capital and operating costs are well assessed. Nevertheless, room still exists to further reduce operational costs. A possible route towards energy optimization and therefore operational cost reduction can be identified through a better understanding of the mixing phenomena. The focus of the present work is that vertical mixing, defined as the cyclical movement of the algal cells between surface and bottom layers of the culture, cannot be completely determined by considering only turbulence, and therefore it is not represented by the Re number. A 3D Computational Fluid Dynamic (CFD) analysis of a conventional RWP was carried out based on a multi-phase “Volume of Fluid” model, in order to investigate the flow field of the culture in the pond. The CFD results were compared with experimental measures on a 20 m 2 pilot RWP. Once agreement among CFD and experimental results was shown, a statistical evaluation of the trajectories calculated for algae particles in the flow was carried out. The aim of this statistical evaluation was to define the level of vertical mixing in different sections of the pond. The model proposed was then used to scale-up the results to a demo/pre-commercial size RWP (500 m 2 ). The standard deviation of the actual trajectory was calculated with respect to the undisturbed trajectory for each section modeled. The results of the simulation showed that a limited mixing is to be expected in RWPs. In the long straight parts of the pond vertical mixing is poor and algae tend to settle to the bottom. Only in the bends the vortexes produced by flow separation move part of the culture from the bottom to the top and vice-versa. This result does not fit with the practice, typically observed in large scale ponds, of reducing vortexes around the bends by placing baffles. The method described can be applied to different pond designs operated at different culture velocities.

SummaryAlgal cultures are usually co‐cultures of algae and bacteria, especially when considering outdoor mass cultivation. The influence of associated bacteria on algal culture performance has been poorly investigated, although bacteria may strongly affect biomass (or derived product) yield and quality. In this work, the influence on growth and productivity of Tetraselmis suecica F&M‐M33 of bacterial communities and single bacterial isolates from the algal phycosphere was investigated. Xenic laboratory and outdoor cultures were compared with an axenic culture in batch. The presence of the bacterial community significantly promoted culture growth. Single bacterial isolates previously found to be strictly associated with T. suecica F&M‐M33 also increased growth compared with the axenic culture, whereas loosely associated and common seawater bacteria induced variable growth responses, from positive to detrimental. The increased growth was mainly evidenced as increased algal biomass production and cell size, and occurred after exhaustion of nutrients. This finding is of interest for biofuel production from microalgae, often attained through nutrient starvation processes leading to oil or carbohydrate accumulation. As axenic T. suecica F&M‐M33 showed a similar growth with or without vitamins, the most probable mechanism behind bacterial positive influence on algal growth seems nutrient recycling.

Many different PBR designs have been proposed for biofuel production, few of them have been tested at pilot-scale, none developed at the (large) scale necessary for a complete and correct evaluation. Thus the main issues that impact on the reactor's performance (i.e., suitable construction materials, efficient mixing, heating/cooling, CO2 supply and oxygen removal), although explored at pilot level, still await evaluation at real scale. Although the main limitations of PBR are the high cost and the reduced scalability, with few exceptions, R&D on photobioreactor design is aimed at achieving high photosynthetic efficiencies and at pushing productivity beyond that currently attainable. The main strategies explored to this end are intensive mixing, light dilution via large external surfaces or internal light conducting structures. This chapter reviews and examines recent advances and innovations in photobioreactor design and operation.