Dietary Effects of a Short-Term Administration of Microalgae Blend on Growth Performance, Tissue Fatty Acids, and Predominant Intestinal Microbiota in Sparus aurata.

Given the potential of microalgae as new aquafeed ingredients, this study focuses on using a blend of microalgae, Tisochrysis lutea, Nannochloropsis gaditana, and Scenedesmus almeriensis, as a dietary ingredient for feeding Sparus aurata juveniles. The growth performance, carcass composition, tissue fatty acid profile, and intestinal microbiota were evaluated after a 30 day-feeding period. A microalgae-free diet was used as control, and three experimental diets were formulated containing 5%, 15%, and 25% of the microalgae blend (MB-5%, MB-15%, and MB-25%, respectively). After 7, 15, and 30 days of feeding experimental diets, biological samples were taken. Growth performance and nutrient utilization were not significantly modified at the end of the experiment. Microalgae inclusion tended to decrease body lipids and affected the fatty acid profile, especially MB-25 diet increased DHA levels. Diet MB-25 promoted appropriate microbial diversity, favoring the presence of probiotic bacteria, such as Lactobacillus, and significantly influencing the fatty acid composition and lipid metabolism in fish. In conclusion, using a short pulse of dietary administration of 25% microalgal blend in S. aurata modulates the intestinal microbiota and lipid composition while maintaining growth performance.

A new control strategy to improve the mass transfer capacity and reduce air injection costs in raceway reactors.

Raceway reactors are still the most extensive technology for microalgae production. However, these reactors have some drawbacks, one of them being a low mass transfer capacity, which provokes dissolved oxygen accumulation and thus reduction of system performance. To overcome this problem, it is imperative to improve the photobioreactor design as well as the operating conditions. One solution is to maintain the dissolved oxygen below defined limits. In this work, a new control algorithm is proposed to improve the mass transfer capacity of raceway reactors while at the same time reducing air injection costs. The main idea of the proposed control approach is that only the necessary amount of airflow will be applied according to transfer capacity demand. This control strategy was first analyzed in simulation and compared with classical On/Off solutions, and subsequently evaluated in outdoor conditions in a photobioreactor of 80 m2.

Scale-up of a Fibonacci-Type Photobioreactor for the Production of Dunaliella salina.

In this work, the previously proposed Fibonacci-type photobioreactor is scaled up and evaluated to produce Dunaliella salina. First, the composition of the culture medium was optimized to achieve maximal productivity. Next, the Fibonacci-type reactor was scaled up to 1250 L maintaining high solar radiation interception capacity of this type of reactor. Finally, the performance of the reactor for the production of green cells of Dunaliella salina at the environmental conditions prevailing in the Atacama Desert was evaluated. Data demonstrated that the proposed photobioreactor allows the temperature, pH and dissolved oxygen concentration to be maintained within the optimal ranges recommended for the selected strain. Both better exposure to solar radiation and photonic flow dilution avoids the use of cooling systems to prevent overheating under outdoor conditions. The system allows up to 60% more solar radiation to be intercepted than does the horizontal surface, likewise, allowing to maintain the pH efficiently through CO2 injection and to keep the dissolved oxygen concentration in acceptable ranges, thanks to its adequate mass transfer capacity. The biomass concentration reached up to 0.96 g L-1, three times higher than that obtained in a raceway reactor under the same environmental conditions, whereas productivity was up to 0.12 g L-1 day (2.41 g m-2 day). Maximum specific outdoor growth rates reached up to 0.17 day-1. Undoubtedly, this technology scaled up constitutes a new type of photobioreactor for use at the industrial scale since it is capable of maximizing biomass productivity under high light conditions.

BIO_ALGAE 2: improved model of microalgae and bacteria consortia for wastewater treatment.

A new set up of the integral mechanistic BIO_ALGAE model that describes the complex interactions in mixed algal-bacterial systems was developed to overcome some restrictions of the model. BIO_ALGAE 2 includes new sub-models that take into account the variation of microalgae and bacteria performance as a function of culture conditions prevailing in microalgae cultures (pH, temperature, dissolved oxygen) over daily and seasonal cycles and the implementation of on-demand dioxide carbon injection for pH control. Moreover, another aim of this work was to study a correlation between the mass transfer coefficient and the hydrodynamics of reactor. The model was calibrated using real data from a laboratory reactor fed with real wastewater. Moreover, the model was used to simulate daily variations of different components in the pond (dissolved oxygen, pH, and CO2 injection) and to predict microalgae (XALG) and bacteria (XH) proportions and to estimate daily biomass production (Cb). The effect of CO2 injection and the influence of wastewater composition on treatment performance were investigated through practical study cases. XALG decreased by 38%, and XH increased by 35% with respect to the system under pH control while microalgae and bacteria proportions are completely different as a function of influent wastewater composition. Model simulations have indicated that Cb production (~ 100 gTSS m-3 day-1 for manure and centrate) resulted lower than Cb production obtained using primary influent wastewater (155 gTSS m-3 day-1).

Life cycle assessment of high rate algal ponds for wastewater treatment and resource recovery.

The aim of this study was to assess the potential environmental impacts associated with high rate algal ponds (HRAP) systems for wastewater treatment and resource recovery in small communities. To this aim, a Life Cycle Assessment (LCA) was carried out evaluating two alternatives: i) a HRAP system for wastewater treatment where microalgal biomass is valorized for energy recovery (biogas production); ii) a HRAP system for wastewater treatment where microalgal biomass is reused for nutrients recovery (biofertilizer production). Additionally, both alternatives were compared to a typical small-sized activated sludge system. An economic assessment was also performed. The results showed that HRAP system coupled with biogas production appeared to be more environmentally friendly than HRAP system coupled with biofertilizer production in the climate change, ozone layer depletion, photochemical oxidant formation, and fossil depletion impact categories. Different climatic conditions have strongly influenced the results obtained in the eutrophication and metal depletion impact categories. In fact, the HRAP system located where warm temperatures and high solar radiation are predominant (HRAP system coupled with biofertilizer production) showed lower impact in those categories. Additionally, the characteristics (e.g. nutrients and heavy metals concentration) of microalgal biomass recovered from wastewater appeared to be crucial when assessing the potential environmental impacts in the terrestrial acidification, particulate matter formation and toxicity impact categories. In terms of costs, HRAP systems seemed to be more economically feasible when combined with biofertilizer production instead of biogas. On the whole, implementing HRAPs instead of activated sludge systems might increase sustainability and cost-effectiveness of wastewater treatment in small communities, especially if implemented in warm climate regions and coupled with biofertilizer production.