A new model to analyze the temperature effect on the microalgae performance at large scale raceway reactors.

In this study a simplified temperature model for raceway reactors is developed, allowing to determine the temperature of the microalgae culture as a function of reactor design and environmental conditions. The model considers the major phenomena taking place in raceway reactors, especially heat absorption by radiation and heat losses by evaporation among others. The characteristic parameters of the model have been calibrated using genetic algorithms, next being validated with a long set of more than 50 days covering different weather conditions. It is worth to highlight the use of the developed model as a tool to analyze the influence of the temperature on the performance of microalgae cultures at large scale. As example, the annual variation of the performance of up to five different microalgae strains has been determined by computing the temperature index, thus the normalized value of performance of whatever microalgae at the real temperature with respect to that achievable at optimal temperature can be established. Results confirm that only strains tolerant to wide ranges of temperature can be efficiently produced all the year around in large scale outdoor raceway reactors without additional temperature control systems.

The oxygen evolution methodology affects photosynthetic rate measurements of microalgae in well-defined light regimes.

Designing photobioreactors correctly is a must for the success of microalgal mass production. Optimal photobioreactor design requires a precise knowledge of photosynthesis dynamics in fluctuating light conditions and hence a method for the measurement of photosynthetic rates in specific light regimes. However, it is not uncommon in literature that experimental protocols used to obtain oxygen generation rates are described ambiguously and the reported rates of photosynthesis vary widely depending on the methodology. Additionally, quite a number of methods overlook certain aspects that can affect the estimated rates significantly, and can therefore affect photobioreactor design. We have developed a method based on oxygen evolution measurements that accurately determines photosynthetic rates under well-defined light regimes. Our experimental protocol takes into account most of the issues that can affect the rates of oxygen generation, such as depletion of nutrients during the measurements and precision of the measurements. We have focused on the basic applications in photobioreactor design and used a dynamic model of photosynthesis to analyze our results and compare them with available published data. The results suggest that our oxygen evolution method is consistent.

Recovery of lutein from microalgae biomass: development of a process for Scenedesmus almeriensis biomass.

In this work an optimized method for the extraction of lutein from microalgae biomass is presented. It has been developed using dry biomass of the lutein-rich microalga Scenedesmus almeriensis. The method comprises three steps, cell disruption, alkaline treatment, and solvent extraction, and renders a carotenoid extract rich in lutein. The results demonstrate that cell disruption is necessary and that the best option among the treatments tested with regard to industrial applications is the use of a bead mill with alumina in a 1:1 w/w proportion as disintegrating agent for 5 min. With regard to the alkaline treatment, the optimal conditions were obtained using 4% w/v KOH with a biomass concentration of 100 g/L for 5 min. Longer alkaline treatments or the use of higher KOH concentrations reduced the yield of the process. Finally, extraction with hexane is optimized. Using a 1:1 ratio hexane to sample volume, a total of eight extraction steps are necessary to recover 99% of lutein contained in the processed biomass. However, the optimal number of extraction steps is six, 95% of the lutein being recovered. In summary, the developed method allows the efficient recovery of lutein from microalgae biomass, it being a scaleable and industrially applicable method.