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Astaxanthin is a high-value carotenoid currently being produced by chemical synthesis and by extraction from the biomass of the microalga Haematococcus pluvialis. Other microalgae, such as Chlorella zofingiensis, have the potential for being used as sources of astaxanthin. The differences between the synthetic and the microalgae derived astaxanthin are notorious: not only their production and price but also their uses and bioactivity. Microalgae derived astaxanthin is being used as a pigment in food and feed or aquafeed production and also in cosmetic and pharmaceutical products. Several health-promoting properties have been attributed to astaxanthin, and these were summarized in the current review paper. Most of these properties are attributed to the high antioxidant capacity of this molecule, much higher than that of other known natural compounds. The aim of this review is to consider the main challenges and opportunities of microalgae derived products, such as astaxanthin as food. Moreover, the current study includes a bibliometric analysis that summarizes the current research trends related to astaxanthin. Moreover, the potential utilization of microalgae other than H. pluvialis as sources of astaxanthin as well as the health-promoting properties of this valuable compound will be discussed.

In this paper, a new photo-respirometry method for determining the rates of the main metabolic processes of microalgae-bacteria consortia in microalgae-based wastewater treatment processes has been developed and tested. The proposed protocol consists on applying dark and light periods to a microalgae-bacteria consortium in the presence of different substrates and measuring the rate of oxygen production. This allows determining the activity of microalgae, heterotrophic bacteria and nitrifying bacteria separately. The method has been optimized in terms of the operation strategy, including the starvation period required, the biomass concentration and the irradiance during the measurements. Results show that a starvation period of one to three days is necessary depending on the nutrient concentration. The optimal experimental conditions determined were a biomass concentration of 0.5 g/L and an irradiance of 200 μmol photons/m 2 •s. Furthermore, microalgae-bacteria samples from seven photobioreactors (indoor and outdoor) with different nutrient sources have been evaluated applying the methodology proposed. Regardless of the wastewater type, the microalgae activity is the main metabolic process, with heterotrophic activity increasing along with the chemical oxygen demand (COD) in the wastewater. Nitrifying activity was only observed when high ammonium concentrations were present. The developed method is a powerful tool to adequately manage and operate wastewater treatment processes using microalgae/bacteria consortia, providing valuable information to model wastewater treatment systems with microalgae and determine kinetic parameters.

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Microalgae-bacteria consortia have been proposed as alternatives to conventional biological processes to treat different types of wastewaters, including animal slurry. In this work, a microalgae-bacteria consortia (ABACO) model for wastewater treatment is proposed, it being calibrated and validated using pig slurry. The model includes the most relevant features of microalgae, such as light dependence, endogenous respiration, and growth and nutrient consumption as a function of nutrient availability (especially inorganic carbon), in addition to the already reported features of heterotrophic and nitrifying bacteria. The interrelation between the different populations is also included in the model, in addition to the simultaneous release and consumption of the most relevant compounds, such as oxygen and carbon dioxide. The implementation of the model has been performed in MATLAB software; the calibration of model parameters was carried out using genetic algorithms. The ABACO model allows one to simulate the dynamics of different components in the system, and the relative proportions of microalgae, heterotrophic bacteria, and nitrifying bacteria. The percentage of each microbial population obtained with the model was confirmed by respirometric techniques. The proposed model is a powerful tool for the development of microalgae-related wastewater treatment processes, both to maximize the production of microalgal biomass and to optimize the wastewater treatment capacity.